29 Nov
2023
29 Nov
'23
10:16 a.m.
-----Original Message-----
From: Tony Duell <ard.p850ug1(a)gmail.com>
Sent: 26 November 2023 06:35
To: rob(a)jarratt.me.uk
Cc: General Discussion: On-Topic and Off-Topic Posts <cctalk(a)classiccmp.org>
Subject: Re: [cctalk] VT100 Monitor Board
On Sat, Nov 25, 2023 at 11:12 PM Rob Jarratt <robert.jarratt(a)ntlworld.com>
wrote:
Hello Tony,
I am working on the schematic and when it is done I will post it for information. However,
I was wondering what you suggest for testing the board once I have done this. Simply
replacing the blown fuse and plugging it in doesn't sound like a good idea. Equally,
not sure if using the light bulb method for limiting current into the PSU is going to help
is it?
Thanks
Rob
> Have you checked the diodes and capacitors
associated with the
> flyback transformer? If something is shorted there. it's the
> equivaent of running a power supply into a short circuit. The input current
will go up.
I have checked all the diodes (in circuit) and they appear to be OK. One
capacitor
may be suspect but without the full schematic I am not sure. I may
have to lift it to check.
Without the schematic you are going to have problems.
With a schematic you can see
(a) Can you isolate certain areas -- for example the vertical deflection syste
because of
my insufficient understanding of electronics.
It gets easier with experience. Looking at every small monochrome monitor
schematic you can find will give you an idea of the sort of things to look for.
if I
can.
The high voltage outputs can't supply that much current and are unlikely to
be lethal. Mains, and even worse the rectified mains in an SMPSU, is a lot
more liely to kill you.
That said, work with one hand in your pocket (current flow arm-to-arm is the
most dangerous) and take care.
I don't see how you can debug a monitor without having the flyback in place.
It's part of the highest power circuit on the board. And it provides voltages for
many other areas.
-tony
Trace out
a schematic of the board so I know what I am dealing with.
Yes, I may have to do that. Historically I have done a poor job of this I do
wonder what the problem is with testing it with the flyback
connected, though...
Only that I know it can produce lethal voltages and I would rather avoid that