> -----Original Message-----
> From: Tony Duell <ard.p850...@gmail.com>
> Sent: 26 November 2023 06:35
> To: r...@jarratt.me.uk
> Cc: General Discussion: On-Topic and Off-Topic Posts <cctalk@classiccmp.org>
> Subject: Re: [cctalk] VT100 Monitor Board
>
> On Sat, Nov 25, 2023 at 11:12 PM Rob Jarratt <robert.jarr...@ntlworld.com>
> wrote:
>
> > > 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.
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
>
> With a schematic you can see
> (a) Can you isolate certain areas -- for example the vertical deflection syste
>
> > > 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
> 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.
>
> > > 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
> 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
