From the schematic, the CRT filament runs off the
flyback (2 brown
wires), so it's not suprising it goes out when the horizontal
output
stage fails.
I also assume that the +53V supply (emitter of Q204) is fine when the
thing fails.
Yes, no problem there.
Good... As I said, 'alwyas check the power supplies' :-)
One problem --
on my schematic the HOT is Q214. There is no Q217.
I'll bet the schematic you are looking at it is for a later reduced-emission
version. I don't have that schematic, but the one I do have matches the
machine I'm working on... an upgraded H88.
Quite possibly. It's the schematic that came with my Z90 (which has
always AFAIK been a Z90, it wasn't upgraded from anything), and it
matches the machine I have.
3) The drive waveform is wrong. I don't have the
H89 schematics
to hand,
but there's often a low-value electrolytic
capacitor (a few uF) in the
There is,. It's C226 (10uf) on my schematic. Also check R254 (1.2R), R255
(100R) and L202 (a small coil).
I don't have my schematic at hand at this moment, but those are all familiar
parts/values... If the drive waveform was disrupted, are there any other
The component references are probably different. Look at the base circuit
of the HOT. Typically you'll find it's driven by the secondary of a small
transformer (the horizontal drive transformer) with some R's and C's
around. It's those you need to check.
symptoms typical? When the display is operating, it
appears pretty much
perfect, until just a few seconds before the HOT shuts down.
Electtolyic caps can do some very strange things!. The capacitor may be
OK when cold, and then fail when it warms up....
Thanks for the tips... I have enough spare parts that I could just send the
whole video section to the graveyard, but it seems a minor problem and a
good education to figure it out and fix it. I appreciate the
elp. --Patrick
What's the fun in board swapping :-)
-tony