Re: Will pay good money for NON working PET 2001 motherboard.

Thanks for the replies.

The cursor seems to be flashing at normal speed, so maybe that means  
the keyboard VIA is good?

Anyway I have swapped around the VIA's and PIA's from one board to  
another, with no change. Of course I have no idea if the parts I'm  
swapping in from the other board are functional either, so in that  
case I have also swapped the two 6520's around between themselves,  
which still leaves the 6522 as slightly suspect, but probably good.

On a side note, I have been able to blindly write a program to display  
inverted characters (white blocks), and run it. It seems to function  
correctly.

Maybe it's time to look at the schematic and see what's around the  
character ROM area, and break out my logic probe too.

As I'm sort of a novice, any further advice would be greatly  
appreciated.

Phil



On Nov 8, 2009, at 7:32 AM, André Fachat wrote:

>
> -------- Original-Nachricht --------
>> Datum: Sat, 07 Nov 2009 22:59:33 +0900
>> Von: Philip Lord <random6000@mac.com>
>> An: cbm-hackers@musoftware.de
>> Betreff: Re: Will pay good money for NON working PET 2001  
>> motherboard.
>
>> First thing I noticed was that there were many keys not working or
>> working sporadically, however I was still able to quickly write a
>> 'hello world' program to confirm that the basic was function
>> correctly. All seemed good until I tried to load a tape. After typing
>> 'LOAD' and pressing return the computer would freeze. I would not get
>> the 'press play now' message, and the tape drive would no longer
>> function. Turning the machine off and on again brought the machine
>> back to life, and the tape drive was able to move again through FF,
>> REW and PLAY buttons. Typing LOAD or SAVE would lock everything up
>> again.
>
> The keyboard could be bad keys, but also the keyboard PIA going bad.
>
> The tape is connected to the keyboard PIA and the VIA. If the machine
> locks up when accessing the tape, it could be one of those.
>
>> 'Commodore Basic' greeting screen was not displaying either, just the
>> flashing cursor.
>
> Is the cursor flashing with the normal speed or faster?
>
> PIA1 (keyboard PIA) also creates the system interrupt. The system
> interrupt controls cursor speed. I don't actually know how an  
> "always on"
> or "always off" cursor would look like.
> You could check the IRQ line if it is always on or always off.
>
>> Anyway, I'm guessing that maybe the character generator ROM has  
>> died???
>
> Don't think so. You'd have garbled characters, but would be able to
> use the machine as before.
>
> I'd check the PIAs, for example by swapping them, or replacing them  
> with
> known good parts. Same for the VIA.
> If they are in sockets, reseating them may already help if you haven't
> done so.
>
> André
>
>
> -- 
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