Discharging a VT100 CRT

Julian Wolfe fireflyst at earthlink.net
Wed Nov 9 12:43:29 CST 2005

Well, you were right.  Something did blow on the VT100 video board, and in a
bad way.  It looks very much like it was that diode you speak of, cause
there's a huge burnmark on the board at the contact points of the diode.  If
that's not an "I died" indicator, I don't know what is.

Can anyone tell me what diode to buy to replace it?  I'm thinking of getting
a replacement video board, and then replacing the diode on that, just in
case it took something else with it.  The whole "y" trace has a brownmark
around it that the diode was connected to, and that has a big cap next to

All in all, this has been a lot easier than I thought to work on.  Thanks
for all your help, Tony, and everyone else too!

-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
On Behalf Of Tony Duell
Sent: Saturday, November 05, 2005 7:03 PM
To: cctalk at classiccmp.org
Subject: Re: Discharging a VT100 CRT

> Yes, I'm in IL.  Are you a business?
> I probably need a VT100 power supply, as I found out it wasn't just the
> flyback that blew.

The PSU rarely fails, and if it does, it's one of the nicest SMPSUs to 
repair since all the control circuitry is on the 'isolated side', the 
drive to the chopper transistor being transformer coupled.

Very often one of the diodes on the vidoe board fails -- one of the 
diodes that rectifies the output from the flyback transformer to produce 
the CRT voltages. This is often the reason that the flyback fails in the 
first place. I would look at those first.


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