TRS80 Model 4P CRT contrast fail

Adrian Graham binarydinosaurs at
Tue Nov 28 17:47:05 CST 2017

> On 26 Nov 2017, at 21:06, Adrian Graham <binarydinosaurs at> wrote:
> I replied to this thread a while back but managed to only reply to Tony and not the list, oops! Rather than using my multi-transistor tester for TR103 I tested it with a DMM in diode mode and it’s almost a dead short from B-E, I get the same reading in both directions so I’m going to order a new one in a bit.

Replying to myself here but to my surprise the replacement 2SC2228 arrived today and the machine is running nicely now, albeit with some screen wobble. I also tested the replacement in my transistor tester and it was correctly identified as a BJT NPN so I should’ve questioned it at the beginning but hey. Live and learn.

It’s currently running the built-in RAM test which is a lot more than it’s done for the last 15 years :)

Cheers folks!

>> Adrian/Witchy
> Binary Dinosaurs - Celebrating Computing History from 1972 onwards

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