EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: jonpaul on October 05, 2020, 08:53:17 am
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Bonjour a tous:
For the Hameg HM103 scope with dead unblanking circuit continued saga from September post asking for parts....
I have replaced the optocoupler, NPN, PNP BF199 BF440, and checked all resistors and trimpot, all are fine.
Blanking logic input pulse is fine, so quite a puzzle.
Last possibility: leaky coupling caps 68pF/2kV, I have seen many posts referring to their failure.
I have no way to test caps here. I have only a variac, VOM and soldering iron!
I ask the Hameg veterans to please inform me:
Could a failed cap just kill blanking, but scope works fine and traces is good otherwise?
How to diagnose if a cap has failed?
Will a failed 68 pF/2kV kill the semiconductors?
where else to look for the problem?
Your assistance is greatly appreciated!
Jon