25 Nov
2017
25 Nov
'17
3:02 p.m.
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