VT100 preventative maintenance?

tony duell ard at p850ug1.demon.co.uk
Sat Aug 22 13:10:19 CDT 2015

> Should I leave well enough alone, or is there preventative maintenance that
> should be done? For instance, should capacitors be proactively replaced. In
> general, I'm thinking about things that, if they fail catastrophically,
> would cause collateral damage.

The main part you want to protect is the flyback transformer. It is very hard to 
get a good replacement now. Flybacks can just fail, but failure can be caused
by defective diodes and capactors on the video PCB. Look at the schematics for
your video board (there are at least 3 versions) for half-wave rectifier circuits that 
produce the CRT and video stage supply voltages from the flyback. You might want
to check or replace those diodes and caps.

A VT100 and models derived from it (VT105, etc) has an SMPSU. Defective capacitors
on that can kill the chopper transistor, but that is in not impossible to replace.


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