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ICOM IC765 Distortion	Reply
by W9RUK on February 21, 2006	Mail this to a friend!
I have an ICOM IC765 that has suddenly developed a significant distortion product, in receive, when first turned. This is most notable on 17 meters and higher. The 20 meter band and lower don't seem to be as badly effected by this. On 17 meters I get what sounds like splatter accross the band which distorts all received signals. If I tune in what might be the offending station, the signal is very raspy and distorted. If I than tune in another, I find the same distortion. No changing of bands, AGC time constant, switching antenna, keying transmitter, etc. has no effect. After about a 45-60 minute time period, it suddenly clears up for the most part. The audio still has a rasp that wasn't there before but not objectionable. The splatter like product also disappears. I have not had any problems previously with this radio and wonder if anyone has had a similar problem or any ideas for me. I do not have any test equipment to use, so trouble shooting has got to be relatively simple. Thank you for your help!! Mike W9RUK

RE: ICOM IC765 Distortion	Reply
by AA4PB on February 21, 2006	Mail this to a friend!
The IC761/765 has a known problem with the plastic VCO trimmers going bad with age. It results in a "watery" sound on received signals on one or more bands. Icom has a service bulletin on it and a replacement ceramic capacitors for about $15. They are a major problem to replace as they are inside a shield can that is filled with wax. I'd send it back to Icom unless you are really experienced in that type of detailed work and have the test frequency counter required to realign it after the capacitors have been replaced.

RE: ICOM IC765 Distortion	Reply
by WB2WIK on February 21, 2006	Mail this to a friend!
Yep, I've seen that in both the IC-761 and the IC-765. It can be band related and also temperature related. The problem in my case was the PLL was on the verge of breaking lock due to component drift in the VCO. The last time I had to deal with this was several years ago and it took quite a bit of troubleshooting, plus the service manual, to find and fix the problem. Icom recommended factory service at the time, but I replaced a trimmer in the VCO and realigned per the service manual (which took only a VTVM and an oscilloscope, as I recall) and it was good as new. Frustrating as heck because this was an 11th hour problem that surfaced just as I was demonstrating the rig for sale! Couldn't sell it that way, had to fix it first. Your problem may not be the same, but the symptoms sound the same. WB2WIK/6

RE: ICOM IC765 Distortion	Reply
by WB2WIK on February 21, 2006	Mail this to a friend!
AA4PB posted similar answers at almost exactly the same time. We both neglected to mention (I just remembered this) that you can "test" to see if this is really the problem or not by simply rapping on the VCO area using a rubber eraser-tipped pencil. Just bang the eraser against the board by the VCO a few times while the rig is experiencing the symptoms, and if this is really the problem, you can either "fix" it (temporarily) or cause it to get worse with just a few small "hits." The trimmer is vibration sensitive, as well as being thermally sensitive. WB2WIK/6

RE: ICOM IC765 Distortion	Reply
by K4LIX on February 21, 2006	Mail this to a friend!
Try this URL for an idea of what is involved in replacing those trimmers. I sent mine off to Groton Electronics and they did a super job for me - very satisfied. www.qsl.net/ka8okh/icom.htm

RE: ICOM IC765 Distortion	Reply
by AA4PB on February 21, 2006	Mail this to a friend!
The sheet I had for the IC-761 stated that there was a problem with the original plastic trimmers they used in the VCO can and recommended a replacement kit of newer ceramic types. I had to unsolder and remove the top from the can. Then turning the radio upside down I used a heat gun to melt the wax and pour it out of the can and into a container. Then I had to remove the remainder of the can from the PCB. Then replace the trimmers. Then solder the can back on the PCB and re-align the VCO, which required a frequency counter as I recall. Then melt the wax in the container with a heat gun and pour it back into the can. Then solder the top back on the can. It was quite a process and after going through that to gain access, I surely would not replace just one capacitor. Mine was an IC761 but I understand that the IC765 is basically the same radio.

RE: ICOM IC765 Distortion	Reply
by ZS6ARF on February 22, 2006	Mail this to a friend!
Hello, All the comments are relevant although in my experience it is usually the lower bands 40 , 80 that gets effected by the trimmer problem. Where I differ is that it is really not that difficult to fix. The biggest problem is the metal case where the lid is soldered (flowed) but some patience and a high wattage soldering Iron will do the trick. I use the XYL's hair dryer to melt the wax which is really the cause of the problem that destroys the plastic trimmers. Do not put wax back into the holder as the ceramic trimmers will not loose their settings. Then although it is recommended to use a frequency counter as recommended by ICOM one can get a acceptable accuracy by using your ears and adjusting the trimmers for each band replaced until the audio (listen on the band you are adjusting)is clear. This is done after the lid is back on the holder. It might be a good idea to have someone with the proper test equipment check the settings but the listening method will get you back on the air with minimum trouble and as you are not adjusting any TX frequency you are quite safe. And last, there is no need to have tpo use the ICOM repalcement trimmers, most ceramic trimmers will do the trick, the biggest problem might be size of the trimmers. 73 Wynand ZS6ARF

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