Batboard

My newly aquired supposedly working COM120A powered up, went through self test after 2 mins and then indicated 5 failures. AF counter, RF counter, RF level meter, Distortion meter, Deviation meter. In GEN mode there is no output. When I put a -20 signal into ant jack and unit in SA mode I see the signal fine but at -5dbm as per 120a. I found a 29 page PDF service manual for the 120C on the net. As per the block diagram I set the 120 to generate a 155.5 mhz at -20dbm signal and injected a 88.5 mhz at -15 into W18 of the Generator converter and saw the 155.5 at -19.8 on my Spectrum analyzer and could change the output level just fine with the 120's scroll wheel
I thought W17,19,20,were ok when I checked a few days earlier. I had unplugged, inspected and reinserted the different trays and looked at electrolytics on Baseband module and every thing LOOKED ok.
There is a red LED on a pc board behind the keyboard that flashes every second but I am getting no more brain flashes!!
I bet WOWBAGGER knows exactly what is wrong and is simple to repair!!
John, VE5PM at gmail.com

First of all, you aren't quite clear about one of your tests: "When I put a -20 signal into ant jack and unit in SA mode I see the signal fine but at -5dbm as per 120a. "
So, are you feeding a -20 signal from an external generator into the 120? It is showing a proper signal (grass line, with a single peak), with the peak reaching -5dBm on the analyzer display? Correct?

I'd suspect what you have is a generator LO not locked - go to the setup screen and bring up the status on the LO's. If the gen is not locked most of the self tests will fail (since the unit cannot perform the loop back test). This may be a problem with the serial bus drivers on the CPU tray - I had a similar problem with mine (and was able to prevail upon service to fix it for me). If that's the case, I'd suggest getting an RMA and having it both fixed and professionally calibrated.

You have a correct understanding of the test in SA mode
I neglected to mention that the 5 LO's displayed in the synthesizer lock test show LOCKED
The unit is new to me and what I do with it doesnt require professional calibration - I just want it to work

OK, then I'd suspect the generator tray, specifically the initial modulator section isn't working.

The flashing LED you describe is the CPU heartbeat - it's supposed to do that.

The analyzer being out is because the unit needs to do a normalize, which needs the generator, which isn't working.

Thank you very much. Thats what I thought, but what do I know, I'm just an old man-a has been that never was(quote from a friend).
If I cant fix it i'll i'll bury it or trade it for a greenhouse kit and go into gardening. In the meantime if someone can help me, email me with a phone no and I will call back. John, ve5pm at gmail

I made the same mistake twice. It is ve5pm2 at gmail

Hello VE5PM

My name is Joseph and I am in Brazil. I have a 120a IFR with the same problem.

You solved the problem of your IFR??

Thanks
José

All,
COM120A/B - At this time in its long life, to settle down the erratic performance you need to replace ALL the surface mount electrolytic caps in the test set. If they have leaked then that mess will have to be addressed too. I use multi layer ceramics in there place. Rocks don't leak anything and last a long time.
Carl N0PXJ