Tek 2465a grid bias and brightness problems


Francesco
 

Hi, I have recently managed to acquire a 2645a, it is in wonderful
conditions with the nvram battery still ticking since 1986. I have already
performed some maintenance work, replaced all the electrolythic caps on the
A2 and A3 boards, replaced the battery with a tadiran sl-850/p, however I
can't find the cause of the only problem the scope has. The traces are very
bright and even with the intensity control at lowest level they are still
visible, I checked grid bias adjustment but it's already at minimum. All
the intensity controls work fine but the lowest level is too bright. I
checked various test points: power supplies are fine with minimum ripple,
DAC reference voltages on A5 board are also spot on, I checked every
component in the grid bias part of the HV board and they test good. Readout
intensity works fine.
I hope in a suggestion here, I don't want to give up, it's a very nice unit
and it will be a shame to leave it like that.
Thanks in advance
Cheers
Francesco

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