Re: Broken P500

From: Rob Clarke <>
Date: Tue, 02 Oct 2012 17:19:27 +0200
Message-ID: <>
WRT to the 6525, a bad one can 'black screen' the system. The one that 
handles the keyboard also controls the 16k bank that the vic-ii sees. 
When I got that batch of 6525's a few months ago I did not have a 
socketed 6525 in any of my cbm-ii machines to test with but I now have a 
P500 with a socketed 6525 and I know that some of the bad ones will stop 
the machine from visibly booting.


On 02/10/2012 17:07, Steve Gray wrote:
> Hi,
> I tested the PLA and it's good.. For those that don't know.. I also 
> have an original working NTSC P500 to test/compare.
> One other hypothesis is bad bank 1 ram. Again, soldered in, which 
> always seems to be the reason I get stuck.
> Steve
>     *From:* Michał Pleban <>
>     *To:*
>     *Sent:* Tuesday, October 2, 2012 3:03:31 AM
>     *Subject:* Broken P500 (was: Commodore 8296GD)
>     Hello!
>     Steve Gray wrote:
>     > My P500 is not happy. I've tested all the socketed main chips
>     and they
>     > are ok. The voltages look ok. There seems to be activity in the
>     system
>     > but I'm not sure where it's going bad. I suspect the 6525 might
>     be bad
>     > but it's soldered in, and since my eyes are going bad I haven't
>     been too
>     > keen on soldering these days. A also need to convert it from PAL to
>     > NTSC, which again will need some soldering.
>     My P500 had recently gone bad too, and it exhibits similar
>     behaviour to
>     yours, including similar activity on address lines.
>     I don't believe a broken 6525 would bring a system down like that
>     - the
>     system is still alive, but the CPU appears to have been lost in the
>     address space. A broken I/O chip will not make it - for example, when
>     CIA breaks down in CBM-II it simply brings the whole bus down and the
>     CPU halts. After looking what might go wrong in the system, my bet
>     is on
>     the PLA chip. I will be working on it in some spare time...
>     Regards,
>     Michau.
>           Message was sent through the cbm-hackers mailing list

       Message was sent through the cbm-hackers mailing list
Received on 2012-10-02 16:00:40

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