IFR COM120B Help Needed

[twbtech]

Hi Everyone
I was wondering if someone could help me if possible, I have a COM120B that has been working perfectly for years, this morning I went to use it and when pushing the front power button, the fans start, unit beeps once, the antenna green LED comes on and that's it... nothing else. I have taken the cover off and measured the supply voltsages as per the manual and the only strange thing is on PIN 5 (analog 5V) and PIN 7 (digital 5V) they are down to 4.6V

The PS was rebuilt 2 years ago by the IFR service agent.

Any ideas & Thanks for your help in Advance.
Andrew

[AdrianH]

It would be very difficult to say but at 4.6 Volts some circuits may not kick in, but why has it dropped? It could be a faulty cap going resistive and taking some current/ something else gone faulty, or it could just be an adjustment that is required.

The Tants where one for going I believe and the large electrolitics on the switcher board, all have been replaced on mine at some time, I have also had problems with one of the switcher circuits going short that does the 14 Volts to the Oven./battery charger side.

Any signs of smoke or the acrid smell of a cap, visual check on the boards where possible?

There was a wowbagger post some years ago that suggests you are only getting to the stage that the keyboard processor is running up you are not getting to the stage of the main processor is up and running, so have a look on that board as well to see if you have a cap problem on there?

See if this helps at all.

http://batboard.batlabs.com/viewtopic.p ... rg#p386120

Adrian

[jeryray]

Does it work on an external 12v supply?
Also be careful you use a large conductor cable from the 12v supply. The initial current draw is like 10 amps, then settles down to about 4-5 amps.

[jry]

4.6V is not enough to run the processor. You have to consider there is more of a drop getting to the actual components.

Chances are a tantalum cap is starting short loading the supply.

Usually that supply is set to just under 5.2 on the analog ...the digital will be a little above 5 volts

[AdrianH]

The original poster has not been on since the 24th June 2018 so this may be a dead post.