Author Topic: HP E3630A Output Drops to Zero Intermittently - Fixed  (Read 184 times)

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Offline Dave Wise

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HP E3630A Output Drops to Zero Intermittently - Fixed
« on: October 18, 2019, 09:26:14 pm »
Something to watch for.  If C27 leaks - even a tiny bit, not visible - it will dissolve the solder mask beneath the cap, allowing electro-migration between two traces that go through there.  One is the -5V reference, and if they short, you will lose all three outputs.  I replaced the reference and a couple other parts before I looked hard at the physical PCB layout, following the -5V traces around.  If all your outputs are low or zero, I think C27 is the first thing to check.  Unsolder it and look at the board underneath.

Hope this helps some other E3630A owner,
Dave Wise
 
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Offline Dave Wise

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Re: HP E3630A Output Drops to Zero Intermittently - Fixed
« Reply #1 on: October 22, 2019, 03:55:34 pm »
I had three false starts before I discovered the leakage.  Since the proximate cause of losing all outputs was the -5V reference line, I replaced the LM336.  No change.  Then I found a 2N2222 whose goal in life is to ground -5V if -12V fails.  Replaced it.  No change.  Then I followed the trace around looking for resistors which could short it if their conformal coating was bad.  Found several suspects, re-soldered with prying to give clearance.  No change.  The last trace segment went under C27 (4700/25, reservoir for +5V display supply) and I noticed the slightest discoloration.  Took off the cap (which was not bulging) and it was a sad mess underneath.  I cleaned with IPA scrub and dried, scratched away the bridge, recoated with nail polish.  Now the instrument is fine and might outlive me.

Dave
 


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