29 Apr
2017
29 Apr
'17
10:29 a.m.
On Sat, Apr 29, 2017 at 5:45 PM, Aaron Jackson <aaron at aaronsplace.co.uk> wrote:
I have measured these again because I thought they
seemed a bit
strange. I must have probed the wrong pad on the circuit board earlier
(my probes don't fit in the CRT header).
Here are all the voltages and they don't seem too promising:
pin 1, green, 4.3v, should be 50v to 80v
pin 2, yellow, 6.6v should be 70v to 100v
pin 3, brown, 12v - fine
pin 4, black, 0v - fine
pin 5, white, 0v, fine, goes to case ground
pin 6, red, 0v, should be 400v to 800v
pin 7, blue, 0v, should be 400v to 800v
The voltage from the brightness control ranges between 2.4v and 5.5v,
and matches pin 1 above.
This looks very much like a problem with the horizontal deflection
circuit. Maybe the flyback transformer, maybe not.
Without a 'scope, troubleshooting is going to be difficult. But
start by testing the horizontal output transistor (Q202 on
the printset). For a start, just check it for shorts and opens. But
if it has failed, don't just replace it, as a problem with the flyback
transformer can destroy the new transistor.
-tony