Re: Educator 64 video board schematics wanted

HI Gerrit,

The TDA1170 has been replaced just to make sure it was not that.  I am
fairly sure that during troubleshooting a couple years back, the NE556 was
swapped and the original put back in but I should recheck that.  You do
make a good point about the socket however.  Maybe a quick replacement is
in order just in case.

I've also replaced most of the caps.  A couple of the NP caps I could not
get direct replacements and I did not replace the largest cap but that
didn't help.  I've also taken out all transistors and diodes and checked
them out of circuit.

The next thing I was going to do was test the potentiometers.  I've used
contact cleaner in them and they seem clean but they should be tested.

Santo

On Wed, Jul 12, 2023 at 11:16 AM Gerrit Heitsch <gerrit_at_laosinh.s.bawue.de>
wrote:

> On 7/12/23 16:36, Santo Nucifora wrote:
> > I am trying to fix a Commodore PET Educator 64 model that has video
> > issues. There is no schematic that I could find for the board marked
> > with a part number of "02-96409 REV 3". Would anyone have a schematic
> > for it?
> >
> > Here is a picture, if it helps:
> >
> https://vintagecomputer.ca/wp-content/uploads/2023/07/Educator64-02-96409Rev3-videoboard-scaled.jpg
> <
> https://vintagecomputer.ca/wp-content/uploads/2023/07/Educator64-02-96409Rev3-videoboard-scaled.jpg
> >
> >
> >  From my understanding, the monitor in the Educator 64 allows for shades
> > of grey (or green in this case) and is not a standard PET monitor so it
> > may be specific to the Educator 64 only. This monitor will run with
> > signals from an unmodified C64 motherboard. The PET 64, however, has
> > extra circuitry on a small daughterboard that changes the video signal
> > to black and white so that a normal PET monitor will work.
> >
> > I currently have vertical collapse on this particular monitor. The video
> > output of the C64 via an external monitor is good so the signal should
> > be good as well. Having a schematic would help with diagnosing the
> > vertical circuit.
>
> Can't help you with the schematic, but the TDA1170 is the IC that
> controls the vertical deflection and a datasheet is easily available.
> The TDA1180 is for the horizontal part.
>
> You might also want to check the socketed NE556 on the left side.
> Sockets can develop contact problems over time and this doesn't look
> like a quality socket. Same goes for all the potentiometers and that
> little switch.
>
>   Gerrit
>
>
>
>