TRS80 Model 4P CRT contrast fail

Adrian Graham binarydinosaurs at
Thu Nov 23 17:32:12 CST 2017

> On 23 Nov 2017, at 20:43, Chuck Guzis via cctalk <cctalk at> wrote:
> On 11/23/2017 11:34 AM, Adrian Graham via cctalk wrote:
>> None of the pots on the video board deal with contrast so I’ve got it out on the bench to remove and test the capacitors. What else can I look at at the same time? Someone else has already mentioned the transistors Q101, Q102 and Q103 (on the yoke board).
> Have you tried replacing C101?  What happens if you temporarily remove
> TR101?

It tests ok at 4816nF with 1.4ohms ESR. I need to work out a way of getting everything connected together outside the case so I can do measurements. I’m hoping it’s something fairly easy to spot as high voltage even at low current is daunting.



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