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Jeff Liebermann Jeff Liebermann is offline
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Default DMM banana jack inputs

On Fri, 22 Jun 2018 10:30:36 -0400, Phil Hobbs
wrote:

On 06/21/2018 05:42 PM, Jeff Liebermann wrote:
Hints:
1. Beware of new and improved.
2. That which is most difficult to replace, is usually the problem.
3. When all else has been replaced, that which remains, no matter how
improbable, is the culprit.


Except that while replacing all that stuff, the real fault blew up
several of the replacements, so it's quite possible to replace
everything and still not fix it!
Cheers
Phil Hobbs


4. When everything has been replaced, and nothing remains to replace,
it's time to give up.

I have a multiyear example of that happening to me. I am the not so
proud owner of an IFR1500 service monitor. Over the years, the power
supply had become more and more intermittent and refused to function
on 117VAC input. However, the 12VDC input does work. In multiple
attempts to fix the problem, I have systematically replaced every part
in the switching power supply section except the magnetics at least 3
times. The last time, I replaced everything with all new parts before
applying power. Something blew up anyway, so I gave up and have been
running it on a 12VDC bench supply for about 5 years.

At one point, I even thought I had found the culprit:
http://www.learnbydestroying.com/jeffl/IFR-1500%20Power%20Supply%20Repair/IFR-1500%20power%20supply%20repair.html
However, the celebration was premature. It died again in about a
month.

My current strategy is to find a 117VAC +5V/+12V only "brick" power
supply and replace the entire power supply. I can live without
battery operation and DC power. However, I can't seem to find
something suitable in a form factor that will fit. My latest scheme
is separate +5V and +12V bricks, which hopefully will fit.

At least I'm in good company:
http://www.repeater-builder.com/test-equipment/aeroflex/aeroflex-index.html
"Also, many old IFRs are having power supply problems. If anyone
would like to do an article on troubleshooting and repair we'd
be happy to put it here."

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558