Re: CBM 3032 (PET 2001N-32), no video?

On Sun, Feb 25, 2018 at 6:58 PM, Sherry Haibara <v.castelli92@gmail.com> wrote:
> Quick update. I built a rudimental PET video mixer according to D'asaro
> schematics to test if the main board was working correctly. The discrete
> components I used don't match exactly the ones on the schematics (resistors
> and capacitors are a little off), so the result is that the external
> monochrome monitor I'm using as test is not syncing correctly on the video
> signal.
> Still, I'm able to see some output. When I turn on the CBM, I see a mostly
> green screen, followed by a black screen, followed by what seems to be a
> single line of text that is repeated multiple times on the screen and that
> keeps oscillating in a diagonal fashion. I'm not entirely sure of what I'm
> seeing, but this seems to suggest that the video generation circuitry on the
> main board is doing something, and that there is some processing going on
> (could it be the BASIC prompt?). I may try to build a better one in the next
> days if I can find the right components.

it looks you're seeing the right output but the monitor can't sync to
both the sync signals you're trying to feed it.

> I will now try to refresh the solder joints on the diode bridge, on the
> capacitor and on the LM7812 rectifier and see if I can get the heater of the
> internal monitor working (and/or if this leads to some difference in the
> measurements).

the heater of the monitor is really independent from the main PET
board. It should light as soon as you apply the AC power to the
monitor PCB, even if no PET is connected. It's fed with the regulated
12V DC through a dropping resistor only.
If it doesn't come on, there is no 12V dc on the monitor PCB or some
connection is broken (wires going to the CRT neck, the dropping
resistor, etc.)

Frank
>
>
>
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