Re: SC502 HV Repair Tips Needed


Ryan Scott
 

I don't have the schematic for that one in front of me, but I recently fixed a very similar problem on a RM-561A.  The HV was dead.  The problem was the flilament winding which was pulled down to -3300V with the cathode.  When I disconnected the filament transformer from the cathode, and disconnected the filaments from the CRT, the HV came right up.  Luckily I had a transformer from another 561 that it appears Tek beefed up the insulation on those filament windings.   Replacing the xfmr brought this 1964 vintage scope back to life.  
Of course, it could also be the multiplier so the way to check that would be to disconnect the multiplier from the xfmr and see if the cathode HV comes up.  Had that problem in a 465 some time ago.
Good luck.ryan N7QJ

On Sunday, September 3, 2017 9:54 AM, "u.piechottka@... [TekScopes]" <TekScopes@...> wrote:


  Hi,

my SC502 is dead now.

First i noticed some problems with instable intensity/focus adjustments, the beam sometimes was very intense, sometimes dimmed. First i mentioned the pots but they seemed to be ok. Then after a while F800 was blown. After replacing it the fuse remained intact but no HV. -15V and +20V are present, output of U860 is positive, both collectors of Q855 and Q850 show positive dc voltages, not oscillation.

Q: What would be the best approach to find the cause for this malfunction?

Thanks - Udo





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