John Robertson wrote:
>
> OK, I've got a couple of WG HV cages for Asteroids and both are
> croaking when warm.
>
> What appears to happen is the HV diode is getting hot just sitting on
> the bench, but not connected to anything other than the HV lead! Ihave
> replaced the HV lead with another from another flyback (colour) and
> the diode still heats up.
>
> Have cleaned the wire, and support post, yet somewhere there is a
> current leak. Have insulated the wire with a silicone collar where it
> goes through the metal cage (and the plastic bit there).
>
> Now, if I remove the outside half of the HV wiring - from the positive
> end of the HV diode - and simply cap the diode with a plastic pen cap,
> then the voltage regulation is stable, and the diode stays cool - as
> expected.
>
> However if I then put the HV wire back on the diode (carefully
> replaced insulators of course!) the sucker gets hot and the HV
> regulation fails (voltage drops). Note that the anode cap is sitting
> inside a very clean, insulated ceramic mug for isolation and safety
> (mine!).
>
> Very curious! Will continue working on it in the next day or two and
> report my findings - but this seems to have a bearing on why some
> cages just seem to die and yet, may be good if the cause of the
> leakage is found...
>
> John :-#(#
>
OK, thanks for the replys - they have helped guide me to where the
problem actually is - the HV diode!
If you have a HV cage that is shutting down after a while check the HV
diode end caps for signs of overheating - they turn black and brittle
when the HV diode is bad.
What I am now finding is some of my supposedly NOS HV diodes have
internal issues that make them effectively act as loads to the system.
The diodes - when hooked to a good picture tube to act as a proper load
- are heating up and then the voltage regulation gives up when the load
increases too much. Trying other HV diodes (all are NOS H1812s), has
some working fine and some failing. I have about ten to test...
So, one major rule - NEVER short the anode of a picture tube directly to
ground to discharge it. We stopped doing that years ago, but some people
still do this. This can cause the HV diode to have issues like the above.
John :-#)#
--
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames)
www.flippers.com
"Old pinballers never die, they just flip out"
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Received on Wed Feb 25 19:28:49 2009
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