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Icom IC-765 Notes

1. new 1N914 itach rare Des wire from W31 D63 Waj new 1N914 l cut this end of D63 D63 and lift Lt A HR PEE D64 Figure 1 PBT modification top and side views 3 2 Modification for improved T R Switching prevents damage to D45 D46 D47 amp D15 on RF Board Parts Needed 47K 1 8 watt resistor 150K 1 8 watt resistor 18853 diode Insu lation for the resistor lead 1 2 3 4 3 3 Remove bottom cover Remove screws from Main Unit and lift board Remove R10 39K and R11 39K near IC 2 Install one end of new R11 150K to foil trace which connects to C13 Insulate remaining lead of R11 and solder it to Pin 3 of IC 2 Install new R10 47K Solder D159 18853 between Pins 3 and 13 of IC 2 Cathode side of diode striped end goes to Pin 3 Modification is complete No adjustment is necessary Reinstall the Main unit and Bottom cover Mod to prevent antenna switch unit failure This modification is covered in the Icom service FAQ The FAQ should be consulted for further information 1 2 3 Remove top cover Locate antenna switch unit at right rear of radio at antenna jack Solder a 0 0047 uF 500V ceramic capacitor to back side of pc board as shown Board removal is not necessary The capacitor is effectively in stalled between ground and the junction of R1 and L1 Reinstall top cover and check for pr
2. Full BK IN 0 022 uF Mylar Capacitor Figure 7 QSK Modification To increase the keying weight in the Full Break In mode add a 0 022 uF ca pacitor as shown in Figure Turn the radio up side down and loosen the front panel to provide access to the board that contains the Fill BK IN switch Solder the capacitor to the two switch terminals closest to the front panel Ie lasen Area of Detail N 90 80 E Q 5 7 cm D 5 376 BFO om M New 51K Resisto Main Unit Figure 8 QSK Sidetone Modification To improve the sidetone remove the bottom cover and locate the area on the Main Unit shown in Figure B Solder a 51kQ 1 watt resistor between the left ends of components labeled 15 and 81 Use an iron with a small tip 15 3 12 Key Clicks Roger VE3ZI uses a different approach to QSK keying with the IC 765 He also presents a simple modification to increase the RF envelope s rise and fall times See http w8ji com keyclicks htm for more information on keyclicksf Improving QSK The PTT timing when using full break in or fast key operated changeover is faulty When you press the key PTT goes low almost immediately but RF does not happen for about 10 ms This is fine and allows time for just about any full break in capable amplifier to change over When you release the key PTT goes high
3. e Remove the trimmer capacitors Note their polarity before removing e Install the new capacitors Note that one side of C45 and C307 is grounded and it is desirable that this be the side attached to the adjusting screw if the capacitors are built that way e Resolder the bottom shield e While you ve got the main unit out do yourself a favour and touch up the soldering on Q7 to prevent the common PTT failure Q7 is a large transistor attached to the aluminum at the side of the board e Reinstall the Main board and connectors e Turn on the transceiver make sure it works and let it warn up e Realign as per the service manual e Replace the BFO cover and the bottom cover e If the transceiver is properly aligned it should be possible to switch between LSB and USB when listening to WWV with no noticeable difference in tone 4 8 Whoosh Noise when Tuning From WONFU WROT KD9KC Tightening the display board mounting screws adding star lock washers between the board and chassis and adding bonding straps or wires were the sug gested solutions to this problem This is a fix for all sorts of strange problems but be careful not to over tighten the screws since that could crack the circuit boards 32 4 9 Paint VA7OJ said that DupliColor Metallic Bronze screen door paint is a close match KGALRU added that Hartzell Manufacturing refinishes Icom and other makes of equipment Hartzell Manufacturing Compa
4. solder at the points where the pins fasten to the small circuit board in the module While you have the display board out look closely at all the solder joints and reflow any that aren t bright and shiny 73 Floyd K8AC 5 Operating Hints 5 1 AM Operating Suggestions From Art Pightling K3XF I have operated AM with many SSB CW oriented multi mode rigs as follows 35 1 Set your microphone gain in SSB by speaking normally into your micro phone as you observe alc action RF output is at max for this Start at zero mic gain and advance until you begin to see alc activity Decrease mic gain just below this point so no alc activity is noted Leave the mic gain at this point for the duration of your AM operation 2 Turn on your compressor Check to see that you do not exceed the alc range as you speak normally into the microphone If you do adjust your compressor so you don t 3 Determine what your full output power is on CW 4 Set your output with the RF power adjust to 20 2596 of that amount Leave it there for the duration of your AM operation 5 Switch to AM You should have very close to 9596 AM modulation with this process and sound pretty good Do some on the air audio checks to assure you are OK 6 Turn on your amp and you will have a good signal without overdriving or splatter Do some more on the air checks with the high power level AM folks love this part if you get disparaging remarks about the orig
5. audio occurring after warmup and that it sometimes affected certain frequency ranges Sure enough there it was the dreaded plastic trimmer problem Being a technician by trade and not wanting to sacrifice my radio to the shipping gods for who knows how long I decided to attack the problem myself Here Pll describe for you how I got everything back into shape for just a few dollars and a few hours of time The repair is not difficult I feel that anyone with proper soldering technique and a decent digital voltmeter can do it But if you feel squeamish about it contact Icom Tech Support http www icomamerica com and they will do the proper repairs for you What Happened What happens is this the plastic trimmer capacitors in the PLL phase lock loop section of the radio are enclosed in a shielded can This can also contains several coils that are covered with a wax to prevent I presume vibration Also in the 765 the PLL board is located directly below the internal power supply Now you would think that the heat would radiate up and away from the PLL unit but enough heat reaches the board to slowly over years cause the wax to flow down into the trimmer caps It then seems to eat away at the plastic dielectric of the trimmers causing the HPL lock voltage s to drift out of acceptable range which in turn causes all sorts of nasty things to occur The raspy audio might just affect a certain range of frequencies or several ran
6. document provide NO WARRANTY not even the implied warranty of MERCHANTABILITY or FIT NESS FOR A PARTICULAR PURPOSE This document may be reproduced and distributed as long as the above copyright notice and this paragraph are preserved on all complete or partial copies The current version of this docu ment may be found at http www qsl net icom manuals html and www gqsl net ab40oj download download html I d like to thank all those whose information I ve used Your contribution to Icom users is appreciated Finally if you see something of your s here that you feel shouldn t be here or that you haven t been credited for or would like changed or or if you see anything that contains errors or think something should be added or deleted please contact me at dstalk at execulink dot com or via the callbook address for VE3HUR 1 Introduction For an older rig the IC 765 causes a lot controversy and passion The consensus seems to be that it s one of Icom s best and that if the PBT pass band tune patent problems hadn t cropped up and Icom hadn t gone to cheaper filters that it would have been close to the very best Today it represents good value as a used transcelver This document is a collection of clippings from the Icom email reflector infor mation from various web sites and other notes I ve amassed on the IC 765 1 1 Warnings Although I ve tried to collect the information in this document from reliable sources the
7. of problems with some of the FL 30 filters used in mid run IC 765s and that there are no filter termination problems 22 6 Computer interface not working Replaced defective L4 in CT 17 Commu nication Interface V 7T Frequency readout jumps while tuning Icom s fix for this is to replace the optical encoder It s long out of warranty by now and I m too cheap for that so I just repositioned the circuit board inside the encoder until the frequency readout didn t jump 8 Frequency changing this one I haven t found yet It is intermittent and sounds like the IF SHIFT is wandering Doesn t happen often and when it does I power down the radio and it goes away I just know it s another cold solder joint but have not had any success locating it 5 0 volt supply is wandering The source of this 5 0 volt supply is IC7 located on the display unit Re moved the cover from IC7 and soldered three pins in it that had never been soldered Several months later the display started flickering between dim and bright I found 2 pins in this module that the solder had cracked these were my soldered connections because the pins are stiff and when you install the module on the display board the pins usually have to bend a little to fit the holes in the display board When the pins don t won t bend the solder gives Be very careful when positioning these pins inside IC7 because the alignment is critical I replaced the three plastic trimmer c
8. or ask me to change mine Either action could easily put one or both of us out of band And in this case I suspect that our channel neighbors are going to be looking very hard for the slightest departure from our strict frequency assignments The only real solution to all this that I can see is for everyone to agree to set their dials 1500 Hz lower than the channel center frequency as recommended by ARRL and as practiced in England and hope that all our dials are fairly closely calibrated Then run our transmit audio as narrow as we can and still retain intelligibility For a rig like my 765 again assuming that my measurements are reasonably accurate I am right on the edge of being legal if I use the full 205 to 2910 Hz audio range I think that we will all have to make a concerted effort to NOT twiddle the dial to bring in a QSO partner on frequency if he she sounds a little high or low The FCC didn t leave us much wiggle room here and a 50 Hz shift up or down in return for a more natural sound could well put part of our transmitted signal out of the assigned channel This has been an overly long posting as is usual when I get wound up on something but I wanted to be sure to emphasize the challenge that we have been given to operate in these narrow channels with amateur equipment that was never designed to be used in such a fashion although obviously it can be Let s all spend a little time measuring our rig s transmit bandwi
9. reduce the intermodulation distortion caused by strong nearby stations Several hams W5YR WOYG K4JAF question the value of this mod W9NHQ recommends PIN diodes and refers to the original QST articles by Rohde 5 Tony VE6CGX finds they work best on top band where the QRN is severe There was some suggestion that even the IF filter switching diodes be replaced Strangely no one seems to know a part number of a suitable diode 17 4 Common Problems 4 1 Antenna Tuner Hunts or Chatters For either of these techniques the transceiver should be connected to a proper 50 2 dummy load Since the IC 765 apparently senses reflected power when tuning it may be worthwhile to perform the final adjustments checks with a reasonable power level for example 40 watts Additionally it may be necessary to adjust C5 as indicated in the Tuner Unit Adjustment section of the service manual 4 1 1 Empirical Technique This is the fix most commonly presented The feedback circuit that controls the tuning motors becomes sensitive after a few months of aging It requires a one time adjustment to correct 1 Remove top cover and locate the antenna tuner board 2 Locate R5 and R10 and set them to the center of their range 3 Set radio as follows Tuner on Frequency 14 100 MHz Mode RTTY 4 After transmit is engaged for 30 seconds 5 Adjust each control R5 and R10 so neither motor tunes while changing from SSB to RTTY and
10. replacement Attach the top and bottom covers speaker plug and top access door Enjoy Rich KASOKH The author assumes mo responsibility whatsoever for damages absolutely nothing is expressed or implied here Perform this repair at your own risk If you feel this repair is beyond your ability please contact Icom Service for repair parts 4 7 Replacing the BFO Trimmers Here are some tips for replacing the BFO trimmer capacitors C52 C45 and C307 These capacitors may have to be replaced if the frequency is unstable in one or more of the modes USB LSB CW Although it is possible to use an inaccurate or even no frequency counter the alignment is much easier with an accurate counter Check its accuracy and or recalibrate it prior to replacing the capacitors e Warmup both the transceiver and the counter e Power off the transceiver and remove the bottom cover Turn on the transceiver and measure the BFO frequencies for LSB USB and CW Power off the transceiver Setting the new trimmers to these frequencies will return the BFO to exactly the way it was before replacing the trimmers e Remove the screws holding the Main board 3l e Remove the cables to J3 J13 and J19 a cable tie may have to be cut e Fold up the board e Unsolder the shield below the BFO e Remove the BFO cover e In order to see the relationship between the copper foils and trimmers it is helpful to shine a light through the top of the circuit board
11. signals I agree completely and defend my use of narrow filters only on the basis of 1 they keep me from hearing a lot of QRM QRN 2 they possibly improve copy somewhat by keeping strong nearby stations from controlling the receiver AGC and 3 I am accustomed to the sound of the receiver while receiving CW my other favorite mode and find it more natural to tune to a 700 Hz signal than to a 1000 Hz signal I had hoped to keep this note somewhat brief with only the procedural steps being described but the length of the end product confirms that I failed A lot can be said on the theory of operation of the 765 which requires that certain of these steps be performed but that is the subject of perhaps another note if enough folks are interested Setup for the PSK31 Program 1 Sample rate whatever works for your system 11025 0 works fine for me and provides a transmitted tone that is within much less than 0 1 Hertz of whatever PSK31 frequencies are selected 2 Center Frequency 700 3 Callsign 4 Inverted QPSK checked as we will be receiving on a lower sideband mode when we select CW for receiving 5 PTT control as appropriate 6 Narrow filter personal preference I like to use it so mine is checked 7 On the main window check AFC and NET Tx and Rx frequencies will both be 700 Hz initially but will change with AFC and NET action Setup for the IC 765 1 Select VFO operation 2 Select SPLIT mode to receive on VFO A and
12. the PLL board down and remove the board Set the radio aside for now With the PLL board in front of you again take note of the shield can with the 4 adjustment holes Our 4 bad caps are under that cover you can see them through the access holes so this cover has to be removed Using a soldering gun apply heat to the corners of the shield cover and use wick to remove the solder from these areas It sometimes helps to gently pry on the corners with a small screwdriver while heating Take your time and don t apply too much force on anything Now flip the board over and remove the lower shield from the area underneath the shield can Using a solder gun apply just enough heat to free each tab on the lower shield Locate the mounting holes for the 4 caps and desolder them using a 15 25 watt iron and solder wick Now working from the top of the board pull the old trimmers out if they didn t fall out already See all that tan gummy stuff inside the can That s the wax that has caused our grief Using a jewelers screwdriver gently dig out the wax from the vicinity of the trimmer mounting 29 holes If there are signs of wax that may later migrate down into the area of the caps later on go ahead and gently remove it taking care to not distort any coils or break any other components If the wax is fairly solid it sometimes helps to apply heat from a blowdryer while scraping After the areas have been cleaned install the new trimmers in the
13. the red wire FLS to one end of the relay coil Connect the other end of the relay coil to W163 4 Cut W154 5 Connect the end b of W154 nearest to the PCB edge to the relay com mon 11 6 Connect the other end R312 of W154 to the relay NC connection 7 Lift the end of R322 farthest from the filter and connect it to the relay NO J13 brown Fo red TO C FL 70 M FL 32A to R312 N J T NER FL 80 C y R322 4 ys x W163 FLS red Figure 6 Pictorial of the Filter Modification 3 9 Using the 250 Hz second IF CW filter in RTTY mode From Dave KD6TO This allows use of the 250 Hz second IF CW filter FL 53A in RTTY mode e Install the optional 250Hz filter according to the instructions if not already installed e Remove the covers to gain access to the Main Unit PCB e Take a 155133 diode or equivalent and solder the positive side to the positive side of D42 accessible at pin 15 of IC11 and the negative side to the negative side of D39 12 e Re assemble and test The CW 250Hz pushbutton will now select the 250Hz filter in both CW and RTTY modes 3 10 New Version of the N6MZ Sidetone Tracking Modi fication Michael Mraz N6MZ author of the May 1993 QST article titled Add Tracking Sidetone to Your Icom IC 765 Transceiver has suggested a new way of doing the modification I d recommend doing the tracking si
14. to make these ad justments but I obtained excellent results with a good digital voltmeter DVM Attach the dvm ground lead to the chassis Attach the positive lead to resistor R6 on the PLL board R6 can be found immediately to the left of the 4 holed shield can that we worked on it s marked on the board Next we ll make a series of adjustments to our new trimmers working from the front trimmer C11 to the back C37 e Set frequency to display 7 99999 MHz and select LSB mode Adjust C11 the front adjustment hole for a reading of 6 5 volts DC on the dvm e Set frequency to display 14 99999 MHz LSB mode Adjust C20 2nd from front for a reading of 6 5 volts DC on the dvm 30 e Set frequency to display 21 99999 MHz LSB mode Adjust C29 3rd hole back for a reading of 6 5 volts DC on the dvm e Set frequency to display 29 99999 MHz LSB mode Adjust C37 rear fora reading of 6 5 volts DC on the dvm e Now check the voltage at the following 4 frequencies to ensure that it is more than 2 volts DC 0 03000 LSB 8 00000 LSB 15 00000 LSB 22 00000 LSB Together Again Re install the power supply taking care to not pinch any of the leads or damage the heat sink fins Now would also be a good time to inspect the big white power supply plug for any signs of damage Several 765 owners have had trouble with this plug again due to heat The plug will turn brownish in color and become brittle Contact Icom Service for a proper
15. transmit on VFO B 3 Set VFO A to CW Narrow mode 4 Using VFO A tune in a PSK signal to a tone of 700 Hz to be centered in the waterfall display much as you would tune a CW signal to that beatnote Since the 765 tunes only in 10 Hz steps you must allow PSK31 to do the final tuning within a 10 Hz range with the AFC function Give the program 3T 10 a few seconds to AFC the signal to the center of the waterfall note the new Rx Frequency and its offset from 700 Hz I find it convenient to tune the 765 dial such that the offset is less than 10 Hz more on this later NOTE A With the PSK signal tuned in and centered in the waterfall press A B and hold it until the function is completed two beeps sound in usual 765 fashion Press VFO A P to transfer control to VFO B Change the mode to LSB KEY STEP increase the dial reading by 0 7 700 Hz Example you tune in the PSK31 station with VFO A with the dial reading 14 071 53 When you have switched to LSB on VFO B change the dial to read 14 072 23 which is 700 Hz higher This is the crucial step which causes the 765 to transmit your PSK31 signal on very nearly the same frequency as you are receiving more on this later NOTE B Return control to VFO A with the VFO A B button Continue receiving in CW Narrow mode with VFO A and transmitting in LSB mode with VFO B WHEN YOU TRANSMIT USING VFO B IN LSB MODE YOUR ACTUAL TRANSMITTED F
16. volt DC at the center conductor of the antenna jack PTT does not operate When the SEND switch is flipped the green RX LED stays lit and unit does not go in the transmit mode Problem may be intermittent No TX output in all modes Problem is traced to no output at J8 on the RF unit Distorted raspy sounding TX in SSB modes Average power is low even at higher mic gain levels Turning on the speech processor seems to help a little CW RTTY and FM seems normal No or low output on all bands with high Icc Inspection reveals burned D1 L1 L2 R1 and or R2 on the ANT SW unit The power clicks off or flutters on and off when the TX power output is increased toward maximum Inspection reveals that the internal power sup ply is unable to handle the current Unit runs fine when the internal power supply is substituted with an external power supply Tuner operates properly when a carrier is present but drifts out of tune in SSB mode Tuner chatters or makes a rattling sound while speaking into the micro phone in SSB mode mostly on upper bands Tuner does not tune on any band Inspection reveals that only one motor is turning Intermittent display S meter may peg and RX TX may disappear when the unit is in the failure mode Floyd K8AC points out that the Icom fix identifies the DP 6A DC DC converter as IC1 This is incorrect the converter is actually IC 7 See Section f T for details on this repair 20 e VFO tun
17. wattmeter suggest that the IMD will be in the 35 dB range or better SSB The following occupied bandwidth power level vs frequency table was obtained on 20 meters by feeding sinewave signals of the indicated frequency into the ACC1 transmit audio input Pin 4 Power output was set to be 100 watts at 1000 Hz as a reference All output power readings were taken with a Bird 43 wattmeter using slugs previously calibrated against an HP 436A precision power meter Frequency Power Output Reference Hz watts dB 1000 100 0 420 50 3 365 25 6 273 5 13 205 0 25 26 1000 100 0 2800 50 3 2820 25 6 2860 5 13 2910 0 25 26 Note that the commonly used half power bandwidth measured at the 3dB levels is 420 Hz to 2800 Hz or 2380 Hz However the FCC defines occupied bandwidth as the range between the frequencies where the signal level is 26 dBc the reference being the level in the passband For the 765 the FCC occupied bandwidth on my unit at least runs from 205 Hz to 2910 Hz for a total bandwidth of 2705 Hz We must be very careful in interpreting these results We have just stated that the actual measured occupied bandwidth is only 2705 Hz while we are allowed a 42 2800 Hz channel bandwidth It would appear that we are legal if we do in fact drive the 765 with audio signals ranging from 205 Hz to 2910 Hz However that 2705 Hz bandwidth does not simply lie within the channel somewhere Very specifically i
18. with the setting of the power control is of no consequence since the sidetone volume is controlled by the monitor gain control you must have the monitor ON to hear 13 the sidetone While I haven t taken the time to measure the sidetone frequency against the received signal pitch my ear says it s the same or extremely close If you don t already have a copy of the 765 service manual you can get one from Icom But the manual they are currently selling is not a multicolor original but a black and white copy However it s a very good copy right down to the large fold out pages and perfectly readable Finding Q16 and R77 is certainly easier with the manual If you plan to give this a try without the manual you can find the two components just behind the shielded BFO enclosure on the main board The BFO alignment information is found in the 765 Instruction Manual on page 47 3 11 Full QSK Keying Improvement The following was written by George W2VJN and appeared in the Frankford Radio Club Newsletter for August 1991 IU George has graciously allowed me to reproduce it here His company International Radio INRAD qth com inrad sells kits for this modification as well as their well known line of replacement filters In the VOX Mode the keying in the 765 is close to ideal There is a 9 mil lisecond delay from key down to RF output and a 10 millisecond delay from key up to RF off The rise and fall times of the RF envelope are
19. 0 Hz is down a bit on the SSB filter skirt and on my rig just barely puts out full power as compared with a 1000 Hz signal which is well within the filter passband and produces full power easily Your mileage may vary as not all filters are the same I did find that lowering the Tx Frequency to 600 Hz or below noticeably reduced the transmitter power output In any event since most folks seldom run over 50 watts output on PSK31 this small power reduction should not be a problem Second the other side of this coin concerns the CW Narrow filters which are effectively centered on 700 Hz If we use a Rx Frequency very far removed from 700 Hz we run the risk of operating on or near the filter skirts with decreased output and possibly some slight phase distortion My tests show that if Rx Frequency remains within about 100 Hz of 700 Hz the received signal remains well within the 765 s 250 Hz filter passband In summary of this point you can operate with a Rx Frequency from about 600 Hz to about 800 Hz with no problem from the 765 receive filters You can transmit at any reasonable frequency above 700 Hz and again no problem But if Tx Frequency is much below 700 Hz your transmitted signal power will be decreased Note B The procedure above specifies that 0 7 is to be added to the received signal fre quency when adjusting VFO B in LSB mode THIS IS THE CORRECT NUMBER ONLY IF THE 765 BFO FREQUEN CIES ARE CORRECTLY ADJUSTED If your 765 ha
20. 25 for 9 01077 MHz Adjust C128 for 9 0106 MHz Adjust L10 for 9 0100 MHz 4 6 Icom 765 PLL Trimmer Repair A Case History Courtesy Rich KASOKH Updated 11 10 01 See Rich s web page http www qsl net ka8okh for his original article 26 I have had my Icom IC 765 HF transceiver for close to 7 years now It has logged many perhaps hundreds of hours of use This past spring however it began to develop some quirks One day while it was receiving on 30 meters during a particularly busy contest weekend I started noticing contest activity showing up on the band The callsigns were recognized as leaders in the sport of contesting and I found it odd that they would be active on this traditionally non contest band Another oddity the signals were weak weaker than I would expect from these high power stations No matter the contest ended that Sunday evening and things appeared to return to normal A few weeks later while operating on 40 meters CW the receiver suddenly drifted 500 Hz up over the course of 5 seconds or so and stayed there A couple of days after that everything received below 10 MHz would become garbled and unintelligible after 30 40 minutes of warmup At this point I decided that my trusty 765 was in need of some TLC A few years ago I had printed out and read the 765 troubleshooting notes on the Icom web i www icomamerica com support troubleshooting ic 765 htm1 and I recalled something about raspy
21. 65DisplayFix html A service manual and the QST review are available at ndex htm contains both service and CI V manu als Ekki DFAOR maintains a comprehensive CI V site ekki civ AT International Radio INRAD sells filters and modification kits for Icom and other radios 8 Change Log V1 00 2002 01 2 e initial release V1 01 2002 01 30 e new high serial number e updated Icom email reflector info e updated antenna tuner adjustments V 1 02 2002 09 10 e KD6TO s filter mod e new sidetone mod e html version no longer supported V 1 03 2003 06 10 e caution about the use of the MC 60A s amplifier e new links section V 1 04 2004 01 22 e updated links section and MC 60A info e added section on BFO trimmers e added W2VJN s QSK mod added W5YR s comments on 60 metre operation e numerous other additions and changes 48 V1 05 2004 04 05 e corrected mod for selectable SSB filters e updated MC 60A info again V1 06 2005 01 10 e added K8AC s intermittent display fix V1 07 2005 03 30 e minor edits V1 08 2005 12 xx e filter termination clarification e VE3ZI s key click mods 49 References 1 Exploring the synthesizer in a commercial mf hf transceiver In Paul Danzer NIII editor The ARRL Handbook for Radio Amateurs chapter 14 pages 14 49 14 52 The American Radio Relay League Inc 75th edition 1998 Mark J
22. CW not keyed Replace defective IC1 Q21 Q15 D46 D47 D45 Q14 Q8 C181 and C179 I think C179 shorted out first causing the antenna relay to stick in the re ceive position even while transmitting Screwing up the transmit impedance caused the oscillation and blew the components All defective components on RF UNIT I think it would be well to replace all 1 uF capacitors on this board FOC SAK ISK kk Spring 2000 No transmit receive OK Replace defective Q14 on the RF unit Replacing this transistor is getting old I checked the ratings on the device and it s operation in this application is well within it s ratings Close inspection of the circuit reveals a possible path from the base thru C170 D45 C174 D47 C179 and RL1 on the RF UNIT R211 L203 L204 C215 RL210 on the ANT SW UNIT and on thru RL13 on the TUNER unit to the rear panel ANT connector This is a real stretch to believe that could be a problem but then I remembered that I have already replaced some of these components So just as a precaution I installed a pair of 1N4006 diodes in parallel opposite polarity across the antenna input terminals Put the radio back on line and the first time I turned the antenna WOW what a racket The loud buzz was only present while the antenna was turning Pulled the antenna lead off the radio and measured 3 4 vac between the radio chassis and the coax Checked the schematic on the T2X rotator and I see that the common betw
23. Icom IC 765 Notes Don Stalkowski VESHUR December 17 2005 Version 1 08 Contents 3 3 4 4 5 6 6 6 6 T 7 7 8 8 8 9 9 9 10 12 3 10 New Version ot the NOM idetone racking Moaiication 13 D Il Full OSK Keying Improvement 14 D 12 Key Clickd a oa e a aa e oa eo A e a aad e a ea 16 BI3 PIN Diode Modo amp oe 4 wee oe dou E Roy Rex E awe Rod Vg 17 4 Common Problems 18 MI Antenna Tuner Hunts or Chatter 18 4 T mpirical Techniqud 18 4 T Alternate Techniqud lll 18 A Problems covered in the Icom service FAQ LL LL LL 19 A3 VOX Oscilate uera OF EE PORE Ross E ADR RO EORR 21 Wa WRAEFsProbemsandFixed llle 22 4 arrier Oscillator Trimmer Adjustment Correctiong 25 4 6 Icom 765 P rimmer Repair A Case History 26 4 Replacing the BFO Trimmers 31 4 8 Whoosh Noise when luning aaa a 32 I Ald s au umen ane ee we RO S ee hp Se ere Ron mE 33 4 10 Cleaning the Display Window LL LL LL a a a 33 4 ixing Intermittent Display 2004 33 D W Keyer peed Rh 9 4 IX Vletre Operatio V D O onnection to an M 6 Using a computer 00A eadset 35 35 36 36 41 41 44 44 46 47 48 Copyright 2002 2003 2004 2005 Don Stalkowski The author and editor of and contributors to this
24. LSB CW RTTY AM FM Dimensions 424 x 150 x 390 mm 16 7 x 5 9 x 15 4 in 17 5 kg 38 6 Ib Output Power AM 10 40 W all other modes 10 100 W Major Options e FL 53A 455 kHz and FL 101 9 0106 MHz 250 Hz CW filters Both 500 Hz and 250 Hz are selectable e FL 102 6 kHz AM filter e UT 36 voice synthesizer e UT 30 tone encoder 2 2 Relation to the IC 761 From Adam Farson VA7OJ AB4OJ The IC 765 was actually a very different radio from the IC 761 These are the principal differences Synthesizer 761 PLL very similar to IC 751A 10 Hz resolution 765 DDS PLL 1 Hz resolution IF filtering 761 PBT and IF shift selectable 765 IF shift only bypassing 9 MHz filter SSB IF filters 761 FL 80 FL 44A Icom s best SSB filter pair also used in 751A 765 FL 30 FL 96 wider cheaper Internal autotuner 761 AT 150 765 Microprocessor controlled memory tuner no preset controls The IC 765 processor is much more advanced than that of the 761 and 751A In the 765 the operating system is stored in EPROM as opposed to RAM in the older radios Only dynamic data is stored in RAM There is also a data bus linking the main processor to the autotuner control processor One of the benefits of the newer control architecture in the IC 765 is the band stacking registers The IC 761 is in fact pretty well a repackaged IC 751A with more filter selec tions a standard rather than optiona
25. REQUENCY WILL DIFFER SLIGHTLY 10 HZ OR LESS FROM THAT OF YOUR CONTACT SINCE YOU CAN ONLY SET FRE QUENCY IN THE 765 TO THE NEAREST 10 HZ DON T WORRY ON AVERAGE YOU WILL BE OFF NO MORE THAN 5 HZ AND AFC AT THE OTHER END WILL SHORTLY HAVE YOU TUNED IN ON THE NOSE THE NET AND AFC CAPABILITIES AT EACH END WILL KEEP THINGS TO GETHER Now all that sounds complicated and long and tedious it does because I almost told you how to build a clock when you asked for the time Operationally it is much simpler 1 2 3 4 Tune in the PSK31 station with VFO A A B and change to VFO B VFO B to LSB and 0 7 higher dial reading Back to VFO A and carry on 38 That is the brief procedure that you do each time you change to a different frequency station but in return for those few seconds of button pushing and knob twisting you get 500 Hz and or 250 Hz selectivity Now for some fine print Note A PSK31 can grab a signal anywhere in the waterfall up to 250 Hz away from center and with a mouse click move it to the center and adjust the Rx Frequency and Tx Frequency to match That is good and convenient But there are two possible gotchas here First we have to be careful to ensure that our transmitted frequency which will be the LSB dial frequency less 700 Hz the AFC controlled offset from 700 Hz remains sufficiently within the transmitter LSB passband to output the power we desire The problem here is that 70
26. Wilson AA2Z Icom IC 765 160 to 10 meter transceiver QST pages 52 55 December 1990 Mark J Wilson AA2Z Icom IC 765 160 to 10 meter transceiver In Bob Schetgen KU7G editor The ARRL Radio Buyer s Sourcebook pages 2 24 2 27 The American Radio Relay League Inc 1st edition 1991 Duane A Calvin AC5AA Icom IC 765 mods revisited QST September 1996 See Straw December 1995 Ulrich Rohde DJ2LR KA2WEU Key components of modern receiver design QST May July December 1994 Rich Guski KC2MK Variable bandwidth tuning for the Icom IC 765 transceiver In Hints amp Kinks 13th Edition May 1992 pages 1 17 1 18 Rich Guski KC2MK Variable bandwidth tuning for the Icom IC 765 QST 1991 Dean Straw N6BV Modifying the Icom IC 765 for better sounding audio and agc QST pages 78 79 December 1995 See Technical Correspondence September 1996 Michael A Mraz N6MZ Add tracking sidetone to your Icom IC 765 transceiver QST pages 39 42 May 1993 George A Cutsogeorge W2VJN IC 765 full QSK keying improvement The Frankford Radio Club Newsletter August 1991 Michael Cobuccio WAIEYP The Icom IC 765 73 Amateur Radio pages 22 25 February 1990 50
27. about 2 millisec onds However in the Full Break In mode the trailing edge delay from key up to RF off is shortened to 2 milliseconds This is a 7 millisecond error and results in the keying sounding choppy at higher speeds It also reduces the average power transmitted Additionally the side tone is also shorter than the actual transmitted character length Both of these problems can be largely corrected by the modifications described below When the 765 is switched to Full Break In the VOX delay capacitor is switched out By adding a much smaller capacitor in the Break In Mode the trailing edges of the keyed characters are not clipped short The price that is paid for this keying improvement is the come alive time for the receiver is increased slightly between keyed characters The value that I have chosen is a compromise between perfect keying and too long of a delay in the come alive time In my radio the keying error was reduced to 3 milliseconds and the come alive time increased from 20 milliseconds to 24 milliseconds In actual operating the increase in come alive time is not noticeable The second modification reduces the delay from key down to sidetone output from 10 to 3 milliseconds and increases the delay from key up to side tone off from 2 to 3 milliseconds This improves the sidetone sound significantly The Frankford Radio Club has also given their permission for reprinting 14 Front Panel
28. almost immediately but RF does not stop for another 10 ms This is low level PTT from the ACC socket the SEND relay is not quite as bad presumably because of its operating delay But it is also the internal PTT function within the IC 765 and causes clipped dots when using full break in So one is almost bound to hot switch on break The fundamental reason for the problem is that PTT on all modes is derived from the VOX circuitry and CW keying uses totally separate timing and circuitry My fix is external I apply keying to the amplifier immediately but delay PTT off by about 20 ms The circuit I use is shown in Figure B The key manual or electronic is connected to the input of this circuit The key output is con nected to the IC 765 keying input and the PT T output is connected to the SEND input output on either IC 765 ACC socket Amplifier PTT input can be taken either from an ACC socket or from the relay output Keeping the SEND input low also keeps the IC 765 internal circuitry in the transmit mode thus preventing the clipped dots I have not had any problems with RF getting into the keying but I suppose it might be prudent to build the circuit in a metal box and use some RF decoupling on input and output It can be powered from the 13 6 V DC available on the ACC socket but through a 78L05 voltage regulator I did consider putting the circuitry within the IC 765 to achieve the same purpose but it would be a bit messy and I have a bo
29. anel frame According to the Troubleshooting Guide there may be a cracked solder joint beneath the DP 6A causing the problem so I set out to remove the DP 6A The wording of the document is a bit vague in this case and I first thought that they were talking about a problem on the display board itself In retrospect Icom was talking about a problem with a crack where one or more if the 8 pins of the DP 6A attach to the circuit board within the DP 6A housing The bottom of the DP 6A can is open and you can easily see where the pins connect to the DP 6A circuit board That being the case you may be able to fix the problem without removing the DP 6A simply by heating the eight pins of the DP 6A where they go through the display board and thus reflowing the solder at the other end of the pin Removing the module from the board is not as easy as it first appears as the holes are plated through and it s difficult to remove all the solder from the holes I used a thin solderwick product from Mouser which I find to work much better than the solderwick sold by Radio Shack Still I had to reheat the pins many times and use a small screwdriver placed between the module and the board to rock it loose You have to be careful here not to use too much heat or force as you might lift the trace pads off of the circuit board Before removing the module I suggest you first just reflow the existing solder on the 8 pins and then reinstall the display board and see i
30. apacitors in the BFO circuits C42 C45 amp C307 per paragraph 5 of the Most Common Service Questions for the Icom IC 765 I found on the ICOM web site Symptom Frequency unstable in SSB modes 9 Replaced the three plastic trimmer capacitors in the Carrier Oscillators C123 C125 amp C128 Symptom CW was transmitting about 2 KHz higher than receive Made it a little grin difficult to make contacts Further paragraph 4 of the above mentioned Most Common Service Ques tions suggest replacing C11 C20 C29 and C37 on the PLL unit I did this as a preemptive strike before they gave me problems I have made several modifications to my 765 in addition to the repairs The tracking sidetone that appeared in the May 1993 issue of QST is a must do I had the variable bandwidth tuning from the March 1991 issue of QST installed but removed it when my frequency changing intermittent arose I will be re installing the W2ISB PBT modification it will allow both IF SHIFT and variable bandwidth as the IF SHIFT is useless but the PBT works very well I have also installed PIN diodes in the receiver filter switching This is what I call a preemptive strike not sure if they improved the performance but a 50KW am station just went on the air about 5 miles from my QTH 23 10 11 xolekokokolokolejoletolelolekoleloeleletek March 18 1998 No transmit receive OK Transmit seems to produce about a 50 watt oscil lation even in SSB and
31. are those used in my cable Figure 13 MC 60A cable for use with Icom IC 765 Icom uses a single wire for Up Down while Kenwood uses 2 wires See Figure for the Icom scheme The wiring for a new cable is shown in Figure 13 Since the IC 765 has power on the Tx Audio line pin 1 a blocking capacitor should be inserted in series with the Tx Audio line This is imperative if the pre amplifier is used A 0 1 uF non polarized capacitor seems to work fine although you might want to experiment to get the best audio quality for your voice I ve noticed that when using this microphone the ALC seems to be a little sticky The microphone impedance should be set to 500 ohms 6 2 Using a computer headset Rick Meilstrup OZ5RM describes how to use a computer headset with an IC 765 A cheap headset 12 15 like the kind used with a computer makes an excellent light weight replacement for a separate mike and speaker 46 In order to connect it to our IC 765 we have to make an adaptor I used an empty film canister Two small sockets are fitted on the can s lid and a suitable hole is made in the bottom of the canister An Icom 8 pin mike plug is fitted with a short length of shielded multicore cable and the other end of the cable is passed through the hole then soldered to the two sockets one for the mike and one for the headphones In order to have the sound appear in both sides of the phones I short circuited the two stereo pi
32. back to SSB Note R5 right controls right motor and R10 left controls left motor 6 Repeat this adjustment to verify proper operation and then check on all other bands 7 Reinstall top cover and return to operation 4 1 2 Alternate Technique This is an alternate adjustment procedure that may be more satisfactory e Subject The antenna tuner on some IC 765s hunts during transmit after the first tuning phase is complete This may start after a few months of use e Information The feedback circuit that controls the tuning motors may be come sensitive after a few months of use 1 Remove the top cover and locate the antenna tuner board 2 Locate R5 and R10 and set them to the center of their range 18 4 2 Set the following controls on the radio as indicated below Tuner On Frequency 7 1 MHz Mode LSB After transmit is engaged for 10 seconds to allow the tuner circuits to tune and stabilize and while still transmitting a Verify V ref at R4 is between 4 6 and 5 3 VDC b Adjust R5 for a voltage that is one half of what was measured in step 5 0 1 VDC measured at R2 c Adjust R10 for a voltage that is one half of what was measured in step 5 0 1 VDC measured at R7 Verify proper tuner operation on all bands Reinstall the covers and return the radio to operation Problems covered in the Icom service FAQ The Icom service FAQ is copyright so I m only going to list t
33. bleshooting Guide http www icomamerica com support roubleshooting ic 765 asp that mentioned cracked solder joints When I looked at the display board layout in the 765 Service Manual I found that the Probable Cause section of the problem description in the aforementioned To remove the tuning knob slide the rubber grip forward and loosen the set screw 33 Guide contained an error The DC DC Converter module DP 6A is IC 7 on the display board and not IC 1 as the Guide states IC 1 is a 16 pin IC of the normal variety while IC 7 is a large square can mounted at the opposite end of the board from IC 1 There s no mistaking the DP 6A module it s the largest thing on the board after the display module itself and is not what you d consider an IC The display board is mounted just behind the display the display module is actually mounted on the display board You gain access to the board by loosening the bottom two of the four screws which secure the 765 front panel to the chassis and removing the top two screws The front panel will then hinge down to allow access to the display board I found it best to turn the transceiver onto its right side to prevent the front panel from hanging down more than necessary You can t miss the label on the large DP 6A module To remove the display board from the front panel unplug the four white cable plugs and remove the two screws that hold the display board frame to the front p
34. bottom cover and set it and the screws aside Now flip the radio face up again Ok see that big black thing on the left side with cooling fins That s your 765 s power supply Our bad caps are below it so we have to get the power supply out of our way It s held in by 4 screws 2 of them go through the left side of the chassis the other 2 go down on the right side of the power supply into two little chassis tabs Remove these screws and unplug the two white interconnect cables going to the supply Lift the power supply out taking care to not damage the cooling fins and set it and the 4 screws aside Now what you see on the left side of the radio is the PLL unit It can be recognized by a few shield cans one with 4 access holes in the top We ll remove this board next First notice that there are a few cables that need to be discon nected There is one grey coax that cannot be disconnected at the PLL board It runs under the chassis to the RF unit Turn the radio upside down The RF unit is on the right side under a shield cover Remove all the screws holding the shield cover down and remove it Notice the grey coax in front of the RF board that goes through a grounding clamp this is the coax we need to disconnect Remove the screw holding the grounding clamp Trace the coax over to the RF board and unplug it from the board Pull the coax back through to the top of the radio Turn the radio right side up again Now remove the screws holding
35. cking I determined that FL30 the 9 MHz SSB filter had a very deep notch on one side of what was supposed to be the flat top along with a sharp spike on one side of the pass band The net result was with my voice characteristics the meters would wiggle but nothing came out on USB Icom sent me a new filter but it had a deeper notch than the original so I installed Fox Tango ssb replacement filters in both IFs and the radio works great now I fell in love with it Started to learn how to use some of the bells and whistles and I think work stations the old Heath stuff couldn t have Then more troubles started 1 Intermittent transmit Cold solder joint on one end of the meter current shunt 2 Receiver dead 2 filter switching diodes shorted in the receiver 3 Receiver dead RF transistor in the receiver went open Checked with Icom and they sent me a copy of the factory update to the main unit to prevent future failure of these components The update has already been installed in my radio and the diode is also installed correctly 4 Intermittent transmit Cold solder joint on receiver Q7 PTT transistor 5 Radio dead Open winding in T1 in the regulator unit This is a small transformer that kick starts the power supply on turn on Previously it was thought that this may be related to mis termination of the IF filters After reviewing the issue Adam VA7OJ AB4OJ and I now feel that it is more likely the result
36. detone another way This mod is much simpler and actually uses the 765 s monitor mixer to beat the TX carrier oscillator against the RX BFO The downsides are that the sidetone volume will vary a little in proportion to the output power setting and that you won t hear the sidetone when you aren t trans mitting i e you can t do CW practice with the VOX button off his is what I did 1 Remove Q16 on the Main board This transistor cuts off the BFO during CW transmit 2 Remove R77 on the Main board This resistor couples the CW sidetone oscillator to the audio T R switching circuit Now when you transmit you should hear the actual tone resulting from the receive BFO beating with the transmit carrier oscillator The volume of the audio sidetone will vary with the setting of the RF PWR control more power louder sidetone If and it s a big if all the mixer oscillators are aligned perfectly when you tune the radio to match the sidetone frequency to the frequency of the received signal you will be exactly zero beat My rig is accurate to within 10 Hz or so If you plan to work on the 765 you really should buy a copy of the service manual it has all the two color drawings that show the com ponent locations on the boards It also has the calibration procedure and theory of operation Floyd K8AC adds the following I installed the new mod and find that it works just as Mike describes The variation in volume of the sidetone
37. dth and do whatever it takes at the audio end to ensure that we do not inadvertently slip outside the channel If I have made any errors here or if something is unclear please let me know Privately if you feel that your comments are not of general interest and to the list if they are I hope that this information will encourage those with appropriate equipment to make use of our new 60 meter band I also hope that it will make everyone aware of the importance of proper dial frequency selection and audio band limits 13 12 George 6 Microphones 6 1 Connection to an MC 60A Microphone A Kenwood MC 60A may be used on an IC 765 if the existing cable is rewired or a new cable is made The pinouts for the MC 60A and the IC 765 are shown in Figure I 44 Kenwood MC 60A Wiring Tx Audio yellow Tx Audio Ground shield Received Audio PTT orange black Chassis Ground green 8 VDC grey Down blue Up red colours are those used in my oem MC 60A cable Icom IC 765 Microphone Wiring Tx Audio Tx Audio Ground PTT Ground 8 VDC Received Audio Up Down PTT Squelch Figure 11 Microphone connectors Chassis connector as viewed from outside 45 Icom Up Down Wiring Up O OA Up Down 9 Down Lara 0 6 470 ln Figure 12 Icom Up Down Wiring MC 60A Icom 2 uF 1 white 1 2 black 470 5 3 blue ap a 5 orange 2 B 7 shield 7 8 green 6 colours
38. e internal keyer can be varied between 6 and 10 wpm slow setting and 12 and 48 wpm fast as shown in figure 10 Slow Fast i 25 8 31 VN ly 8 P 20 _ _ 36 Pa 10 15 43 TR 127 46 6 10 12 47 Figure 10 CW Keyer Speed 5 4 Sixty Metre Operation The IC 765 appears to work on sixty metres Here s George s W5YR summary of tests he performed I have completed several tests on my 765 and present the following results for those who might be interested in using a 765 on 60 meters The 765 is typical in many respects of equipment of the late 80 s and early 90 s All measurements were made from computer generated transmit audio signals introduced via Pin 4 of ACCI thereby avoiding any effects of the microphone preamp etc As most 765 owners know snipping a single diode opens up the transmitter to the entire tunable range 41 My unit Serial No 2437 purchased in August 1990 provides the following performance PSK31 Using the suggested dial frequency of 5346 5 kHz USB 1500 Hz below the channel center frequency of 5348 kHz the 765 produces 40 watts PEP output from a PSK31 IDLE two tone signal with a visually undistorted RF envelope waveform as viewed on a scope The corresponding average power is 20 watts which confirms the lack of distor tion More power can be obtained but I would refrain from operating at more than 60 watts PEP I have not measured IMD at either of these levels but experience with the scope and
39. een the two motor windings and one side of the brake solenoid are connected to the frame of the rotator This point is also connected to the chassis of the rotator control box via the control cable If I had a poor a c ground at the top of the tower it s a crank up so I do it is conceivable that while power was being applied to the motor and brake the ground potential at the top of the tower would actually float due to IR losses in the rotator control cable This is what I found to be true and this floating ground potential is what is coming back down the coax inner conductor and blowing components in the RF UNIT I plugged the controller into a 3 pin to 2 pin ac adapter that lifts the ground and the buzz went away I have since corrected my grounding problem and it has been almost a year with no further failures in the rf unit So to those of us that lose components in the rf unit check your ground between your rotator and radio 24 12 After modifying my Henry 2K 3 for QSK I observed that each element was shortened during QSK operation This originates in the 765 during full break in and was cured by adding a 047 uF ceramic capacitor across the normally closed contacts of the FULL BK IN switch This allows the VOX delay circuit to complete the element I found the same modification in The Frankford Radio Club Newsletter August 1991 except they used a 022 uF Mylar Capacitor I should read my notes and then I would not have to re i
40. f that doesn t fix the problem Just to make sure of the integrity of the land patterns I carefully sanded off the green coating to reveal the underlying copper While the patterns looked perfectly OK I tinned them with a light coating of solder just in case If you do this be very careful to keep the solder out of the hole as it s very difficult to remove it once it s there voice of experience It was at this point that I re read the Icom wording and decided that they were really talking about the solder joints at the other end of the pins where they connect to the DP 6A s small circuit board So I heated each of the 8 pins of the module so that the solder reflowed at their connection to the circuit board Be careful there because the pins appear to be held in place 34 only by the solder and they can easily be moved out of place during this step If so you can gently bend them back into line with needlenose pliers when you re done Correct pin alignment is essential to being able to reinstall the DP 6A onto the display board If you are ambitious enough to remove the module getting it back in place is just slightly less difficult than removing it I had to solderwick all the remaining solder from the holes in the board then use a fine point awl to clean the holes a bit It was also necessary to use a fine file on the module pins to make them fit the now slightly smaller holes Be careful if you heat the module pins to remove excess s
41. ges or all In my case it just affected everything below 10 MHz How do I Fix it Only one way remove the plastic trimmers from the PLL board and install ceramic replacement units We ll go step by step removing that nasty wax sub stance or most of it anyway and re align the vco s according to the service 2t manual While we re in there we ll check out a few other things that may need attention Time s wasting so let s get started What You ll Need e Soldering iron 15 25 watt e Solder wick to remove solder from traces and shield cans Soldering gun here we want something on the order of 100 watt 60 40 rosin core solder I use Kester Rosin Core 44 1 and 2 phillips screwdrivers Small pair of nippy cutters wire cutters Smaller the better Small jewelers type screwdrivers preferably plastic handles or similar ad justment tool e Digital voltmeter Of course you ll also need the replacement trimmer capacitors The capacitors we ll be replacing are designated C11 C20 C29 and C37 C11 and C20 are 10pF picofarad while C29 and C37 are 7pF Now here s where I begin to deviate from the book a bit First let me say without equivocation I have nothing against Icom service or ordering replacement parts from them However in this situation I had the parts in hand to do this repair and they work fine But if you feel that you should get these parts from Icom by all means do s
42. hat my 165 stays on 24 7 365 as a precaution against drift and in connection with some other activities In any event each time you set up for another station you will immediately find out if your adder is correct and if not what the correct one should be Just use whatever value gives approximately the same Rx Frequency values with CW Receive and LSB Receive As a final disclaimer please note that most if not all micro processor controlled Icom rigs prior to the 765 change the dial frequency reading by a fixed amount 40 when the mode is changed I know that was true up through the 761 Obviously the procedure given above would have to be altered to take that dial reading change into account Since I do not have access to any other Icom rig perhaps someone else can pioneer one of the earlier Icom s for us I apologize for the length of this note but I felt that more 765 owners would feel confident to try this operating style if I provided a little more than just a bare bones do this and then do that procedure I find that the few seconds required to set up for a new station are well invested in return for the capabilities provided by the narrow filters Please direct any questions to me privately unless you feel that others might share your concern and would be interested in the answers I especially invite users of other makes of rigs to see how this procedure appropriately modified works with their systems 5 8 CW Keyer Speed Th
43. he problems covered in it Refer to Icom nttp www icomamerica com for their FAQ Unit will not transmit or receive on all bands Very low noise from speaker Display and controls all seem to work properly Dead spots in the bottom 250 kHz or so range of each band when radio is cold Dead spots may eventually get smaller then disappear as radio warms up No RX TX when unit is first turned on but will return if VFO knob is spun or if power is cycled on and off a few times No RX TX or distorted RX TX on one or more bands Distorted SSB audio sounds raspy and rough Some bands may sound OK Problem may be temperature related Frequency unstable in SSB modes Drastic change in audio frequency response between USB and LSB i e USB audio has too much bass while LSB audio has too much treble USB LSB RX frequency response may be equalized to a degree by adjustment if the front panel IF Shift control TX frequency response remains poor No or very low RX sensitivity 19 Distorted RX on strong signals BC band RX sensitivity may be low or marginal Intermittent RX sensitivity Problem seems mechanical Banging on case or switching between RX amp TX may temporarily restore sensitivity The recommended fix is to replace RL13 on the tuner unit In my case the new relay was fine for about a month then the problem redeveloped RX disappears when outer shield of coax is connected to the antenna In spection reveals 6
44. hen you are done Ok now the AF VR Unit has no 8V power So we need to get this 8V power from the spare 8V power pin 5 of J15 on the MAIN UNIT I found some extra push in pins from an old VCR tape player Add an extra push in crimp pin into pin 5 of the female connector for connector J15 Next run a wire feeding through the tie wraps to the AF VR UNIT Find another push in crimp pin Connect the 8V wire to this pin Then push this pin into pin 7 of the male connector which plugs into J304 on the AF VR UNIT One item I did but not necessary is to use a thicker gauge wire for the ground return between the AF VR unit pin 8 J302 and the ground pin on the MAIN UNIT pin 1 J15 21 I also ran the shielded audio cable from the mic pre amp and the VOX input along the metal chassis and away from the noisy harness it was tie wrapped to This helped some but not as much as the power cable change With this mod I now have very very clean audio from the mic pre amp I would highly recommend this mod It took me 2 hours to do 4 4 WS8AEF s Problems and Fixes From Paul M Playford W8AEF I have received several emails regarding my experiences with my IC 765 so here they are First my 765 is s n 002313 purchase new about 1990 After a couple weeks in the operating position I sensed that something was wrong couldn t make any contacts Nobody would answer my calls on 20 meters Put the 303 401 back on line and no problems After much che
45. in of your rig tell them you are using this configuration until you finish your pair of 4 400s modulating a pair of 4 400s excited by your 765 5 1 1 Comments on the IC 765 on AM Adam Farson VA7TOJ AB4OJ had this to say about using the IC 765 for AM The IC 765 is not really characterised for AM transmission It fakes out AM by injecting an exalted carrier at the virtual carrier point In AM mode the radio transmits only one sideband whilst the newer DSP radios IC 756 IC 756Pro Pro II generate a mathematically perfect DSP AM A3E signal with the correct carrier sideband amplitude relationships I would not endorse the IC 765 as a high end AM rig The receiver is OK for SWL ing but lacks a synchronous demodulator 5 2 PSK31 CW Receive and LSB Transmit From George T Baker W5YR I have been asked by several fellow warblers to document the exact setup I use with my Icom IC 765 that allows me to receive PSK31 signals using the 500 Hz and 250 Hz filters In the 765 and in many other rigs of its vintage filter selection is tied to mode selection and the narrow filters are available only in the CW Narrow or RTTY Narrow modes Additionally the 765 allows 250 Hz filter use only in CW Narrow mode in which the 500 Hz filter is already engaged 36 Peter G3PLX has made a strong case that narrow filters prior to the filtering operations within PSK31 have little beneficial effect on improving print in the face of strong adjacent
46. ingis erratic Sometimes skips frequencies in a certain area of VFO knob travel 10 Hz display digit flutters instead of changing incrementally when the VFO knob is turned slowly e Loud high pitched squeal emanates from inside radio May be intermittent e T X monitor gain seems low even at maximum volume settings Radio has good mic gain and the transmitter works OK e A mechanical whine emanates from inside radio in T X only at certain power levels Transmitter works OK e CI V interface does not work Unit will not communicate with computer 4 3 VOX Oscillates From John Bielefeld K1JEB I have come up with the reason why my IC 765 VOX oscillates The 8V power for the Mic Pre amp comes from the Main Unit Board But daisy chains through to and from other boards This causes some transients to be induced in the 8V power line The line is also made of a small gauge wire The resistance on this line is high enough for these transients to be quite large enough to trip the VOX Also if you listen to the transmitted signal via the internal monitor you can hear some of the digital noise generated The solution is 1 Remove the 8V power pin 7 from connector J302 AF VR UNIT 2 Remove the 8V power pin 3 from connector J103 NB SW UNIT 3 Connect The 8V power pin which came from pin 7 from connector J302 AF VR UNIT to pin 3 to connector J103 NB SW UNIT You may have to cut some tie wraps to do this Just add some new tie wraps w
47. ir proper positions and solder them in Be sure to clip the leads flush with the board underneath so they don t touch the lower shield At this point inspect all the traces underneath the shield can for possible cold joints and touch up with a little solder as necessary Icom recommends doing this before re attaching the lower shield so I suspect they have seen problems with solder joints here so it s best to give it a good look over Reassembly Re attach the lower shield to the underside of the PLL unit Re attach the top shield can cover the one with 4 holes taking care to orient the cover so you can see the trimmers through the adjustment holes and solder the corners Mount the PLL unit back into the chassis taking care to not pinch any connecting cables Re attach all connectors Re route the grey coax to the RF unit attaching the grounding clamp Attach the coax to the jack on the RF unit Replace RF unit shield cover With the radio right side up connect the plugs to the power supply but do not put the supply back in the radio yet You can lean it up against the left side of the chassis for now Plug the AC cord in and attach some sort of antenna dipole piece of wire whatever Turn the radio on Don t worry if you can t receive anything You probably won t right now as the new trimmers need to be adjusted Alignment Remember radio is right side up facing you Now the Icom service manual says to use an oscilloscope
48. l internal mains power supply and a built in AT 150 There are also considerable circuit differences on the MAIN IF board between the IC 761 and IC 765 2 3 Filters From Adam Farson VA7OJ AB4OJ The FL 80 is the preferred standard filter The FL 80 FL 44A combination is used in the IC 751A and IC 761 The FL 30 has a 6 dB bandwidth of 2 3 kHz The FL 80 is 2 4 kHz wide at 6 dB but has a considerably better shape factor than the FL 30 1 6 vs 1 8 Replacement of the FL 96 455 kHz SSB filter with either an FL 44A or an INRAD 455 2 4 is worth considering as a means of improving adjacent channel selectivity From Don VE3HUR I installed the FL 102 AM filter and did not notice any difference 2 4 Power Supply From Mahlon K4OQ The internal power supply in the 765 is essentially a PS 35 in a slightly different case This being the case the DC power connectors between the supply and the rest of the transceiver are the same as any other ICOM standard six pin DC power connector INCLUDING the two AC power lines watch how you wire your connector in other words The 765 will run off of 13 8 VDC just fine assuming that you connect your external DC supply in lieu of the internal supply 2 5 Trimmer Capacitors Icom has stated that all IC 765 s were made with plastic trimmer capacitors From Bill WA9MXQ although the DDS LPL trimmer on some units is ceramic How ever Adam VA70J AB4OJ thinks that later radi
49. ng or vice versa and that is the number that you add to the VFO A dial reading in Step 8 instead of 0 7 An example VFO A dial is 14 071 53 You find that you have to set VFO B dial to 14 072 24 instead of the 14 072 23 we used in the example in Step 8 The difference is 14 072 24 less 14 071 53 0 71 So the frequency value for your radio to add to the VFO A dial reading will be 0 71 instead of the ideal 0 7 It works the other way as well Suppose that your dial reading is 14 072 22 Subtracting this from 14 071 53 gives 0 69 for your number In both cases one of the BFO frequencies is off by 10 Hz one way or the other This change from 0 7 makes no difference in system performance you are merely correcting for a small discrepancy in 765 alignment However if the cor rection is more than a few tens of Hertz you probably need to realign the BFO frequencies With the proper dial increment value in place you can switch between VFO A and VFO B and except for the few seconds it may take the AFC to make its correction you should get perfect copy while receiving in either mode Again on average you will almost always be within 5 Hz of correct centered tuning and that range will provide good print throughout Should your rig drift about you might find that you need to change the actual frequency value you use as the adder but mine has remained very constant at 0 7 since I last realigned it a few weeks ago I should also mention t
50. ns on this particular socket There is no provision for PTT Instead I use VOX and adjust various controls on the 765 The audio quality is on par with my SM6 mike so say my friends On my own adapter I added another jack for a separate push button PTT switch from an old computer game The microphone is connected to pins 1 and 7 the headphones series or parallel depending on impedance to pins 8 and 6 and PTT to pins 5 and 6 Inside the IC 765 pin 1 is connected via 1820 ohms of resistors to 8V and this nicely powers the electret element 7 Sources of Online Information The Icom America page http www icomamerica com contains some informa tion on the IC 765 as well as the all important service FAQ Icom has instruction manuals online at support The IC 765 and CT 17 manuals are available The Icom page at qsl net http www qsl net icom is probably the most comprehensive source for Icom rigs There is an Icom email reflector Visit for subscription info The current archive is at and an older archive is at archive icom icom html Adam s VATOJ AB4OJ page http www qsl net ab4oj contains IC 765 information in the downloads section Rich KA8OKH has a detailed page on trimmer capacitor replacement See www qsl net ka8okh icom htm A graphics free version is available by substitut ing icom2 htm for icom htm Floyd K8AC has a page detailing the repair for an intermittent display at http www kBac us 7
51. nvent the wheel Now that it has been almost a year since the last failure I have more time to operate and reflect on why I have kept this radio I am a DXer and contester and I feel this is the best radio available for this type of operating I am particularly pleased that I have been able to keep my electronic trouble shooting skills sharp so I can repair my own equipment because had I not found my own grounding problems I would still be blowing components regardless of the radio I was using de Paul Some days you are the QSO some days you are the QRM WSAEF ZF2TA 1992 FOOPLA 1997 8Q7AA 1998 XZ0A 2000 4 5 Carrier Oscillator Trimmer Adjustment Corrections From Mahlon Haunschild K40Q RTTY Shift Frequency adjustment appears on page 6 10 of the IC 765 service manual All frequency measurements taken from the top of RA84 25 WAS Adj Conditions STEP 1 Freq display 14 10000 MHz RTTY mode 92 850 Hz S3 NORMAL Transmitting STEP 2 92 170 Hz STEP 3 53 REVERSE STEP 4 FM MODE TS Adj Conditions STEP 1 Freq display 14 10000 MHz RTTY mode 92 170 Hz S3 REVERSE Transmitting STEP 2 S2 850 Hz STEP 3 53 NORMAL STEP 4 FM MODE Adjustment Measurement Adjust C123 for 9 01145 MHz Adjust C125 for 9 01077 MHz Adjust C128 for 9 0106 MHz Adjust L10 for 9 0100 MHz Adjustment Measurement Adjust C123 for 9 01145 MHz Adjust C1
52. ny Inc 2533 Technical Drive P O Box 808 Miamisburg OH 45343 Phone 937 859 5955 Fax 937 859 5954 4 10 Cleaning the Display Window Dust manages to accumulate on the inside surface of the display window A partial cleaning can be accomplished by simply removing the front panel and cleaning the exposed parts of the window For a more thorough cleaning the actual plastic window must be removed William Diamond WROT suggests the following procedure The escutcheon is held on by thin double faced tape Use a hair drier and heat up the escutcheon and use a very small dental pick or sharp knife point to get under a corner of it and lift it off Remove the small Phillips screws and the glass will come right off When you get ready to put the trim back on heat with the hair drier and reinstall it 4 11 Fixing Intermittent Display Courtesy Floyd K8AC Sce Floyd s web page http www k6ac us 765DisplayFix html for his original article For quite a while my 765 s display had been plagued with a flicker in the brightness A light rap on the top cover had always restored it to normal intensity After a few months of this the display no longer was illuminated at all when I turned the transceiver on Again a rap on the top would cause the display to turn on I d always suspected a cold solder problem somewhere on the display board and recently ran across the description of an intermittent display problem in Icom s IC 765 Trou
53. o Here are the Icom part numbers to ask for Icom part e 4610001130 trimmers C11 amp C20 order two e 4610001000 trimmers C29 amp C37 order two Now having said that you can also get suitable replacements from Digikey www digikey com They have to have leads spaced 4 5 mm apart be ceramic and of course be the proper capacitance I found these Sprague GKG series ceramic units http www spraguegoodman com 305 305p4 htm1 to be more than ad equate Digikey part e SG1029 ND 3 5 10pF ceramic white Sprague part GKG10024 I used this 10pF unit for all 4 caps Why Well C11 and C20 were 10pF anyway but Icom recommends in their service notes that C29 be changed from TpF to 12pF for ease of adjustment C37 is was 7pF as well so I figured why not try a 10 there as well No worries the 10pF works just fine for all 4 replacements 28 Let s Start Begin by laying your 765 on a CLEAN surface a clean towel to keep from scratching your radio So as not to cause any confusion here throughout this repair keep the front of the radio facing you Remove the little door that covers the adjustments under the top cover and set it aside Remove the screws that hold down the top cover Remove the top cover by gently lifting from the rear then pulling back Detach the internal speaker lead noting the direction of the plug and set the cover and screws aside Now turn the radio over and remove the
54. older so as not to change their alignment relative to one another After reinstalling the module I checked over the rest of the display board for suspicious looking solder joints The display module itself attaches to the display board via dozens of small contacts that are soldered to lands on the board There was a lot of resin between those contacts and I scratched most of it off with the awl point and then reflowed the solder on all of the contacts When I removed the module I found that the only traces on the module side of the board were those that joined two of the holes to the ground plane on the board Since the module is held pretty securely by the eight pins it s unlikely that the small land patterns surrounding two of the holes would be damaged by movement Results After reinstalling the display board I plugged in the 765 and crossed my fingers while hitting the POWER button The display appeared at full brilliance im mediately with all functions working perfectly Prior to performing the fix there was always a slight delay before the display came on even when the intermittent display problem was not apparent Removing and installing the display board in the 765 is easy enough that you might first want to try heating the pins of the DP 6A module with it still in place on the board That may get the pins warm enough at the other end to reflow the solder there If that doesn t work then remove the DP 6A module and reflow the
55. oper transmitter operation This modi fication prevents failure of R1 R2 D1 and L1 3 4 Improved monitor volume For radios with serial numbers below 2000 1 2 3 4 Set radio for 8 MHz in LSB Adjust C226 for 1 to 1 2V at R201 Verify that it goes to 3V at 7 9999 MHz Change R85 10K on main unit to 4 7K 3 5 4 5 rear of radio gt e Figure 2 Rear of antenna switch circuit board Extended TX Mod Remove top and bottom covers From the bottom of the radio locate the matrix board which is next to the front panel Find diodes D50 D51 D52 D53 D54 and D55 Cut one leg of D53 Assemble the radio and stay legal In addition if you wish to use the antenna tuner the following mod is required From Rick Robinson K8DXN 1 2 Remove top cover Locate tuner control PCB It is in the rear of the rig from the marker switch board Locate plug going to J103 Find grey wire going to Pin 8 on J103 named TUNM on circuit Remove grey wire that all done deal 3 6 Better AM Audio 1 Replace AM rectifier diode with schottky for better audio 3 7 QRP Mod With this circuit connected to the radio the power output is adjustable between 0 and 100W For best results leave the RF power control at maximum and adjust for desired power using R2 2 47K Shielded cable 9 Volt 9 alkaline R1 R2 y battery _ 20K S_ gt to ALC a jack Figure 3 QRP ada
56. os came with ceramic HPL VCO trimmers and recalls that his s n 29xx IC 765 did 2 6 Serial Numbers and Dates The first Icom advertisements that I ve found were in magazines in May 1989 The last major distributor s advertisement was in March 1994 The highest serial number I ve heard of is over 5500 From the serial numbers that have been posted in the Icom reflector I d guess that the distribution is about Olxxx 1989 1990 02xxx 1990 03xxx 1991 1992 04xxx 1992 1994 2 7 Icom Email Reflector There is a moderated Icom email discussion group To subscribe to it visit mailman qth net mailman listinfo icom or send an email with the subject subscribe to icom request mailman qth net An archive of the group is at http mailman qth net pipermail icom An even older archive is at http www qth net archive icom icom html 3 Icom IC 765 Modifications Sources of this information These mods have appeared in many places including http www mods dk and in messages from Lee Wells and Adam Farson VA7OJ ABA4OJ but the sources I first used were Jean F Tanguy VE2KAD and Don VEIAOE 3 1 W2ISB PBT mod This modification was originally designed by Gerd Henjes W2ISB 1 Cut or lift cathode end of D63 2 Add a 1N914 solder anode end to anode of D64 3 Cut W31 brown wire and solder to cathode end of D63 and cathode end of new diode IF SHIFT button out PBT IF SHIFT button in IF shift
57. ptor for IC 765 51 is used to turn off circuit when radio is not in use or QRP operation is not desired Radio Model R1 value R2 value IC 761 765 ATK 20K IC 720 A 735 740 745 751 A 275A H 2M IM IC 725 726 728 729 736 737 A 220K 100K 06 01 94 CJR For the IC 820H use the values for the IC 761 765 The IC 781 IC 765 and the IC 820H all have the same ALC characteristics Control voltage 4 to 0 volts Input impedance More than 10 K ohms 3 8 Selectable SSB Filters This mod was on my 765 when I purchased it I don t think it s the best way to do it but it works This unit has different SSB filters than a stock IC 765 An FL 70 2 8 kHz is used in place of the FL 30 2 3 kHz as the standard SSB filter In addition an FL 80 2 4 kHz is selectable via the 250 Hz button on the front panel The FL 80 is installed in the space allocated to the optional FL 101 250 Hz CW filter Filter 6 dB 60 dB FL 30 2 3 kHz 4 14 kHz FL 70 2 8 kHz FL 80 2 4 kHz 3 84 kHz 10 This modification is illustrated in figures through Bl R312 AN b FLO R322 FLS AN d Figure 4 The Circuit Prior to Modification Matrix Unit 250 Hz FL70 R312 9 o p FL80 R322 9 lift R322 d end OEG SRU S 109L 9V relay W163 8V Figure 5 Circuit After Modification The following steps perform the modification 1 Cut the red FLS and brown FLC wires from J13 2 Ground the brown wire FLC 3 Connect
58. re is absolutely no guarantee that any of it is correct You are strongly encouraged to verify all information on your own In particular if modifying or reparing the transceiver heed the following e Check as many sources as possible to verify the modification fix e Understand the modification fix Know what it does how it does it and what circuit changes are requried Be sure that the modification fix actually implements those changes e Be aware that even though a modification fix may be acceptable for some radios it may not be suitable for your s Numerous production changes normally take place during the life of a radio and in theory every radio could be unique Calvin 4 illustrates this fact 2 2 1 If you re not qualified to do it or don t completely understand the radio and the modification fix don t touch it Either use a competent repair facility or leave the radio alone If you do discover an error in this document please inform the author s so that the information can be corrected General Information Description Features Automatic antenna tuner with tuning memory Direct Digital Synthesizer DDS Band stacking registers Built in 500 Hz CW filters 9 0106 MHz and 455 kHz IFs Built in keyer power supply and CI V CW pitch control RIT ATX controls 99 tunable memories Specifications Frequency Coverage Tx 1 8 3 5 7 10 14 18 21 24 28 MHz bands Rx 100 kHz 30 MHz Modes USB
59. s not been recently aligned a simple test will enable you to correct for any mis alignment and still use the procedure In Step 10 above when you have returned to VFO A verify that the PSK31 signal is still centered in the waterfall and note the RX Frequency reading in the 39 window In particular note the offset from 700 Hz Now press VFO A B to return to LSB mode If your 765 is correctly aligned you will be within a few Hertz of the same Rx Frequency and within a few seconds the phase scope will be centered Note the total frequency difference between Rx Frequency with VFO A and with VFO B after the AFC has settled down That is the total frequency difference with which your signal will be received at the other end and is the amount that the other station s AFC will adjust for your signal If the required frequency change is over 10 Hz then your BFO frequencies are off However this is easily compensated for without realignment of the 765 With VFO B simply adjust the dial reading slowly up or down in 10 Hz steps until you find the dial reading in LSB mode that gives the smallest Rx Frequency difference between using VFO A and VFO B That will also be the dial reading that comes closest to centering the phase scope and gives you good print When you have the right value the signal should sound exactly the same in either receive mode except for the added noise etc in the LSB mode Subtract that dial reading from the VFO A dial readi
60. t extends from 205 Hz above our suppressed or dial frequency of 5346 5 Hz or at 5346 705 Hz on the low end to 5346 5 Hz plus 2910 Hz or 5349 41 Hz on the high end So taking my 765 as an example we find that if we do use modulation fre quencies from 205 to 2910 Hz our transmitted signal will extend from 5346 705 kHz to 5349 41 kHz Is this legal The FCC defines the total channel width as 2800 Hz centered at 5348 kHz This means that the channel boundaries are 5348 1 4 5346 6 Hz on the low end and 5348 1 4 5349 4 kHz on the high end And so the answer is not quite Our lower transmitted bandwidth limit is 105 Hz higher than the low boundary but our upper limit is actually 10 Hz above the channel boundary Now that is close enough to call attention to the accuracy of my measurements since I could be off only a few Hz on the high end where it counts and the upper limit would just fit within the channel But let s work with what we have with the knowledge that measurement tolerances are involved So we are left in an individual decision situation Each of us should either measure the occupied bandwidth of their transmitter as I did and or just play it safe and do whatever it takes to restrict both the low and high end of the modulation frequency range to buy some headroom and ensure that we do not crowd the upper channel boundary Remember that with a rig like the 765 and most like its generation we have no external con
61. trol over the transmit bandwidth as we do in the PRO and PRO2 for example So our only recourse to be on the safe side is to limit the audio frequency range to gain a few hundred Hz safety margin The 765 transmit bandwidth is determined by the properties of the FL 30 filter operating at about 9 MHz and the FL 96 at 455 kHz There is a fix to this problem but one which I fear will cause even more problems than it might cure That is simply set the dial lower in frequency than 1500 Hz below the channel center frequency by a sufficient amount to squeeze the actual transmitted bandwidth into the channel limits If we do that we can drop the dial down to 5346 45 kHz This will place the lower 26 dB point at 5346 655 kHz while the upper 26 dB point will reside 2705 Hz higher or at 5349 36 kHz Result Our 2705 Hz bandwidth is now safely placed within the allotted 2800 Hz channel with 55 Hz to spare on the low end and 40 Hz headroom on the high end Close but legal if everything is completely accurate Not much room here for error So what is the problem Well if I set up my 765 like that and you set up your Brand X rig to the dial frequency recommended for that channel 5346 5 kHz then 43 my audio will differ from yours and vice versa by the difference in dial frequencies assuming complete accuracy of calibration That means that I will sound 50 Hz off frequency to you So either you will change your dial out of habit
62. x which also includes a Writelog keyer and SO2R circuitry There is one problem with my solution When the key is pressed the amplifier PTT is energized even if the VOX button on the IC 765 is not depressed I could not find an easy way to overcome this because of the IC 765 design issue described above but in practice it is not serious as the amplifier will not be energized if it is not switched to the operate condition The ARRL review rated the IC 765 s CW waveform as good but adds that a weighting increase is required with speeds over 25 WPM when using QSK in order to maintain a 1 1 dot to space ratio 16 IC 765 Key In 2N7000 PT 2N7000 22 ms stretch T Figure 9 VE3ZI QSK Adapter CW Waveform The rise and fall times of the IC 765 keying are about 2 5 ms the guru W8JI says this is too short I have increased it to about 4 5 ms by changing C108 on the main board from 4 7 uF to 10 uF Note this is a tantalum cap I tried increasing it further but got lopsided rise and fall times which sounded mushy The keying works by turning on crystal oscillator Q35 4 buffer Q34 hard then shaping the keying via PIN diode D85 M1204 through C108 R169 R281 So far as I can establish there are no later stages keyed although with a microscopic circuit diagram it s not all that easy to be certain 3 13 PIN Diode Mod Paul W8AEF replaced diodes D23 D47 and D49 on the RF unit with Hewlett Packard PIN diodes to

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