Discharging a VT100 CRT

Julian Wolfe fireflyst at earthlink.net
Wed Nov 9 16:51:13 CST 2005

Yep, you know your stuff Allison.  C102 and 103 are both 50v caps according
to the schematic.  Should I replace them with equivalent electrolytic 100v
caps?  I'm not an electrician, but I've built working stuff with a soldering
iron when given the right parts.

If I can build this into a better VT100 and not have to open it again for a
good long time, it'll be worth my time and trouble now.

-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
On Behalf Of Allison
Sent: Wednesday, November 09, 2005 1:21 PM
To: cctalk at classiccmp.org
Subject: RE: Discharging a VT100 CRT

>Subject: RE: Discharging a VT100 CRT
>   From: "Julian Wolfe" <fireflyst at earthlink.net>
>   Date: Wed, 09 Nov 2005 12:43:29 -0600
>     To: "'General Discussion: On-Topic and Off-Topic Posts'"
<cctalk at classiccmp.org>
>Well, you were right.  Something did blow on the VT100 video board, and in
>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.
>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
>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

Check the diode first as often they survive.  If it didn't it may be 
the 1A 1000V device (1n4007 will work) at CR102.   The cap is correct value
(22uf) but about half the required working voltage so it shorts after a 
long time. I forget if it was C102 or c103 and the working voltage should 
be at least 100V but not more than 160V.   or so memory says.


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