ICOM 736 repair

This year my ICOM 736 had some problems. The first issue was a failure in the CAT interface. At some point I noticed that my computer log could not communicate with the ICOM transceiver anymore. It happend to be at the same time when I updated my OS to Windows 10. So I was put on the wrong track when I started my troubleshooting since in the past I had a lot of problems with Serial-to-USB adapters. I thought the new OS might be incompatible with the adapter I am using. But finally it became clear that the new OS did not cause the communication problem.

So I had to dive into the schematics which I found on the internet when searching for a ICOM 736 service manual. The CAT interface is located on the PCB inside the front panel. So I had to open the transceiver and to take it quite a bit apart:

Open ICOM 736

Some measurements quickly revealed, that the driver transistor for the CAT interface was defective. Since I had no SMD transistor at hand I replaced it with one universal type in a TO-92 housing from my junk box:

Repaired CAT interface

After carefully reassembling the transceiver the CAT interface was working fine again. But a few weeks later another problem turned up: Receiving SSB and CW was not possible, the audio sounded like I had some IF filter problems or the band pass tuning was set to narrow. Receiving AM and FM worked fine. So I could not use the ICOM 736 anymore and was left alone with my Elecraft K2.

Yesterday when I tried to participate in the SSB part of CQ WW contest I finally was so annoyed by operating SSB with only 10 Watts output of my K2 that I took my ICOM 736 and tried to repair it. Luckily the problem was easy to find – a ribbon cable connector for the band pass tuning potentiometer had some contact problems. So within half an hour the ICOM 736 was fixed and I could easily made some more contacts in the contest.

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