[Premium-Rx] 2050 PS fixed!

[Paul Wende]

Good morning fine RX people.

I have fixed the 2050! Thank you to all who replied with suggestions on what
to look for. My first pass at it was after 10PM, at which time no work
should be done on expensive equipment, as I have learned from past mistakes.
I gave up at midnight after chasing my tail for 2 hours. Last night, I
decided to put the scope on the 5V lines, after corresponding with Baruch,
who suggested replacing the big electrolytic, thinking that maybe my Fluke
is reading the average DC level and there is lot's of AC on the line as
well. (Don, you were right on the nose with your suggestion, although I
didn't get your mail until this AM) The 5V main filter cap only had 90mV of
ripple, while the output of the reg. was 1.6VDC ripple. This must be the
problem, I thought. Tore apart the supply again and changed out the
electrolytics on the cct brd. Put it back together and Shazam! Green light
on A2, Fault light out and display working. I was very happy as you can well
imagine. RX works perfectly and another 2050 is back to life. I changed the
primary power supply tap to 130VAC as well, (an idea I had when I had my
last 2050 a few years back) and that dropped the 14VDC on the input of the
5V reg down to 9V. Thus, there is now only a 4 volt drop across the reg. vs
10V. Power dissipation went from 27W to 12W. Quite a significant
improvement. Also drops the voltage going into the +/- 15 regs as well, but
I forgot to measure those as I was too excited.

Thank you again for your assistance. I am still looking for a service manual
so if you know of one, please let me know. Have a look at the pictures of my
rig and the failed parts. You can see that they have been excessively
heated.

http://www3.telus.net/ve7khz/

Kind regards,

Paul Wende
Arrow Electronics Inc.
Semiconductor Product Marketing Manager
Western Canada
ph  (604)422-6931
Fax (604)421-5030