From: Gabriele Bozzi (mabuse68_at_gmail.com)
Date: 2006-06-08 23:33:06
Hi Richard,
What puzzles me is the fact that without the 6502 you get the same
"reduced" screen height.
I would say that, first of all, some issues with vertical deflection are there.
In my humble opinion when you pull out the 6502 you should see a full
screen, even if the ram is bad you see eventually irregular garbage
but on full height.
It could be that your PET is OK but the vertical deflection circuit is
not working or end of scan is out of sync and what you see as garbage
is, in reality, the startup screen but with each line of the message
strangely interlaced.
After keyboard input does the garbage changes? Can you enter a simple
basic loop thet prints on the screen and observe any behaviour?
Furthermore: on the user port of the PET you can extract a composite
video signal. in "The PET revealed" you can find how and I have seen
schematics on the net about this: you can rule out if it's a video
problem by using an external monitor.
I do not have the schematics here, I can't be specific.
I would check the analog video board. check for cold soldering or for
damages in high voltage coils (often mounted on paper or carton rolls,
they tend to break after a while). Be careful of high tension
discharge even after minutes from power off.
Best Greetings
***********************************************
Gabriele Nicola Bozzi
SANAE VoF Beveren - Belgie
A: Maybe because some people are too annoyed by top-posting.
Q: Why do I not get an answer to my question(s)?
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
***********************************************
On 6/8/06, r.lagendijk@hccnet.nl <r.lagendijk@hccnet.nl> wrote:
> Hi everybody,
>
> I'm trying to repair an PET 2001-8C. When I turn the PET on it displays a
> lot of garbage on the screen. But just on the 3rd quarter of the screen.
> It's the same garbage every time.
>
> I switched or tested the TTL's in the video circuit but nothing changes. I
> switched the 6550's main RAM with video RAM but also no change.
> I switched the 6550 Char ROM with another ROM now there is different
> garbage on the screen so the ROM is being read.
>
> I replaced the 6502 but no change. The PET should display without the 6502
> running so I did some test without the 6502 installed.
>
> I took some pictures:
>
> http://www.xs4all.nl/~lagendr/Diverse/PET 2001.htm
>
> I reseated all chips that are in sockets. The video circuit chips are now
> also in sockets (not the cheap ones.)
>
> Is there anybody who has a idea what's wrong with my PET?
>
> Greetings Richard
>
>
> Message was sent through the cbm-hackers mailing list
>
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