Evening! > OK... Firstly, measure the voltage on pin 8 of the monitor PCB. Can you get > it to swing from 0 to around 12V?
Yes, it tops out at 11.82V. > Scope the video output from the CPU board (on pin 2 of the monitor PCB). Is > it a good TTL level signal? Yes. Given that it’s TTL and a 3-wire connection (composite plus H&V sync) I should be able to feed that into a PET monitor shouldn’t I? Wish I hadn’t given away my ‘big’ TRS80 Model 4 :/ > Measure the voltage on pin A of the CRT base PCB. Expect around 60V here 60.3V > Check that C101 is not shorted. You could try the machine with it removed > to see what happens. > > Have you checked the TR103 on the CRT base PCB? It tests as 2 diodes which is correct for a bipolar transistor I believe. Cheers Tony, A