2 Feb
2013
2 Feb
'13
11:43 a.m.
Thanks for the suggestions.
I've looked for visible arcs as carefully as I can, and have been
unable to see any. I've cleaned and resoldered the connections to the
transformer, and removed and cleaned the anode connection to the CRT. I
don't know if you can remove the anode connection at the flyback end, so
I haven't fiddled with that.
Normall yyou can't disconnect the EHT (high voltage, whatever) wire at
the flyback transfoerm end. It's soldered to the EHT rectifier diode
whigh is encapsulated i nthe potting compound opf the flyback.
Is it reasonable to assume at this point that the arc is *inside* the
flyback cover? Is it possible that a component failure outside the
It's certainl;y poissible for the flyback transformer to break down
internally in thus start sparking. At this poiint, I might think that was
quite likely.
transformer could cause arcing in the flyback, or does
it mean that the
flyback itself is at fault?
What is certainly possible is for components on the video board to damage
the flyback transofmer. Leaky diodes or capactiros can increase the load
on the flyback and casue it to run hot. When I was at Bristol we had some
VT100s that ate flyback transfomers, A new one would last for a few weeks
at most. Replaceing the diodes on the video PCB got the flybacks to last
for many years.
I suspect an internmittant breakdown in any high voltage capacitors
9smoothign the first anode votlage, etc) could cause glitches. The
votlagbe is less than the final anode voltage, but it's still around 800V
in most monitors (sorry, I am not a PET expert). Some monitos had
capacitors with built-in spark gaps to protect the circuitry in the event
of a CRT flashover. These look like normal disk ceramic caps but have a
'bit' on top with a slot in it. THat's the cpark gap. If oyu have nay of
those, cleam the spark gaps before worrying aboput flyback problems. They
might be flashing over occasionally.
The flyback transformer appears to be unobtainium
(although if someone
knows different, I'd love to hear about it). I guess I'm in the market
for a PET video board....
Somebody is goign to have to figure out how to make flyback transofmers.
The model IC engine crowd make their own ignition cols and do vacuum
impregnation, so it is _possible_
-tony