[Premium-Rx] Collins HF2050 problem

[Paul Wende]

Richard,

If you can figure out which coloured wires are the 15VDC ones, (I think
red/blue???) pull the board plugs and measure R on those 2 pins on each
boards' socket to find a short. Start with the main A2 board, the big
motherboard on the top, the one the 2 memory boards mount on. That one is
loaded with tantalums and I have found numerous shorted ones over the years.
The boards come out real easy, all stainless hardware and a joy to work on. 

If I think of anything else, I'll post.

GL

Cheers 
Paul
VE7KHz

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Message: 1
Date: Tue, 29 Dec 2015 16:28:02 -0400
From: Richard Pederson <rpederson at eastlink.ca>
To: premium-rx at mailman.qth.net
Subject: [Premium-Rx] Collins HF2050  problem
Message-ID: <1AE78ECF-2A22-4E6D-9DB5-D8D69A805F95 at eastlink.ca>
Content-Type: text/plain;	charset=us-ascii

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