Re: OT Hameg HM103 blanking


Ray
 

Jean,Well ... I can attest that Hameg scopes and owners :) also exist in the US.As I used to own a 204 and still own a 507.Alas I have not run into the specific problem you discribe.By they way the button labeled CT activates a build in component tester. It puts pn junction curves as well as capacitor and res respomses onto the screen. (In circuit as well)One of the reasons I got the 204 & the 507 which also have this.This function alone is worth fixing your 103.Bon chance.RaySent from my T-Mobile 4G LTE device------ Original message------From: Jean-PaulDate: Sun, Oct 18, 2020 03:16To: TekScopes@groups.io;Cc: Subject:[TekScopes] OT Hameg HM103 blankingBonjour a tous:

Have a Hameg HM103 scope found at a flea market in Paris for EU7, dead unblanking circuit but otherwise OK.

I have replaced the optocoupler, CQY80N, NPN, BF199 PNP BF440, and checked resistors and trimpot, all are fine.
Blanking logic input pulse OK, so quite a puzzle.

Last possibility: leaky coupling caps 68pF/2kV, I have seen many posts on EEVblog referring to their failure.
But I have no way to test caps here. I have only a variac, VOM and soldering iron!

I ask any Hameg veterans (perhaps in Germany or elsewhere in EU) 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

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