From: MAY Peter (peter.may_at_environment.wa.gov.au)
Date: 2003-11-07 03:52:39
Last night I swapped the 6520s over, it made no difference, likewise
swapping the video ram 6550s with two other 6550s made no difference.
Keyboard is still dead as well.
Interested to note that when I unplugged the 6540 Character ROM, it gave a
white screen and the two flashing cursors were still prominent, but in
negative/inverted.
Over the weekend, I'm going to check voltage on the 5V rails and maybe
replace some electrolytic capacitors hanging of the voltage regulators. I
always suspect electrolytics in old equipment!
Please elaborate more on how the systemboard LED can be used in diagnostics.
Thanks for everyone's friendly advice, I feel that I'm approaching this
restoration in a more systematic method now.
Regards
Peter
3:690/462
http://www.geocities.com/SiliconValley/Network/9166/junkbox.html
-----Original Message-----
From: William Levak [mailto:wlevak@cyberspace.org]
Sent: Thursday, 6 November 2003 1:17 PM
To: CBM Hackers (E-mail)
Subject: Re: Expert PET advice sought
The keyboard runs through one of the 6520's. Swap the 2 6520's and see if
the keyboard will work.
Is there a LED on the mother board? If so, there is a built in diagnostic
that can be run by jumpering the user port and keyboard connector.
Is the video RAM the same IC as main RAM? If so, you can switch them and
see if the screen is better.
It as not likely the address bus. If it were, the ROM's would not read
correctly and you would not even get the message you did.
On Wed, 5 Nov 2003, MAY Peter wrote:
> I'm trying to restore an old CBM PET 2001-8 at home. I need expert advice.
> I've gone through the clean-up and reseating the chips in their
> sockets phase which fixed a bad connection on a BASIC ROM chip.
> The screen display looks something like this:
>
> *** COMMODORE BASIC ***YTES FREE
> SIC ***YTES FREE
> []cursor
> READY.
> []cursor READY
>
> It's got me stumped, I have two cursors flashing!
> Keyboard is inactive, cassette motor runs briefly on start-up.
> I was suspecting a possible memory problem, but hoping it was
> sonmething else. 6550 SRAMs have not been made for a long time!
>
> Can anyone help with a possible diagnoses?
>
> Regards
> Peter
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