Re: We are KILLING our HV diodes...?

----- Original Message -----
From: "John Robertson" <jrr@flippers.com>
To: <vectorlist@synthcom.com>; <vectorlist@synthcom.com>
Sent: Saturday, April 22, 2000 12:58 PM
Subject: Re: VECTOR: We are KILLING our HV diodes...?

> The very high charge, especially when just turned off, is present on
the
> anode but ALSO on ALL stages of the cascade.

RCA and GE tv sets... :*)

> As you probably know the cascade is a chain of hightension diodes
built in
> a solid state housing.
> The discharge can cause the underlaying diodes in the cascade to
discharge
> THEIR charge through the "upper" diodes, thus blowing them.

I believe this- the current surge through an arc can be huge!

> IE, the charge can eventually blow from linetransformer THROUGH the
entire
> cascade.
> Sometimes these units are built together in a single housing, making
the
> exchange even more expensive.

Most all TV flys are made this way now...

>
> Just one tiny little resistor, costing almost zilch, can prevent
this.
>
> Check this out, some TV's have a build in discharge unit almost
exactly the
> same construction as you described, only with a built in resistor.

Usually about 600 meg (thats right!)
HV probes use it...

> Now, I think he is REALLY on to something here, and feel it is our
best
> interest to consider following his recommendations, especially as
one of
> our most serious problems relate to both Flyback (Linetransformer or
> HighTension overseas) and or the HV diode (like on the B&W Vector
games).
> We settled on a 3 to 5 watt 1M resistor as having the best chance of
not
> internally shorting, yet doing the job with little risk to the
diodes.

Ooooo... a bit low... 600 meg will discharge a tube in 20 seconds
tops!

WG vector flys aready have it built in, the static crackle when turned
off is
the HV going down. Any TV set that turns off silently still has 30 KV
on the tube...
Some sets have no resistor, but flash the screen brightly on purpose
when turned off to kill off a lot of HV- these go down to 5-10 KV
still dangerous...

Aaron Howald
ahowald@w-link.net
(just wanted to add SOMETHING; I have been silent to long)

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Received on Sun Apr 23 02:02:52 2000