[Premium-Rx] Collins HF2050 problem

[Richard Pederson]

After finally getting some time off over the holidays I decided to listen to my Collins HF2050. It has been sitting on a basement shelf for about 6 years, since I last used it and it was working great then. 

I turned it on and nothing. No screen, no lights, what a disappointment. I checked out all the power supplies and the 15VDC supply nearest the transformer fails under load (and the transformer buzzing increases too) . This 15V supply outputs a nice 15.1VDC when the interface cable to the main board is unattached, but is zero volts otherwise. The supply seems to be fine, both the BD240 and 2N3055 test fine. 

I should also mention that I have checked out that 15VDC PS board (not the tantalum caps) and replaced some of the other capacitors in particular the disc capacitor on the (LM273) regulator IC, pin 13. 

As a quick test to check if the problem is within the PS itself or upstream,  I substituted in my bench power supply to supply the 15VDC and that too was drawn down in voltage. So all indications are that the issue is not PS related but somewhere within the main system. 

But without a schematic or service manual to reference finding the issue somewhere on one of the multitude of boards and display is almost impossible.

Any ideas or hints on where to look or test would be appreciated.

Cheers,
Richard