A little help needed restoring our 8296SK please... :)

asbesto · Post by **asbesto** » Thu Feb 16, 2012 9:25 am

Hi everybody,

we at our computer museum are trying to restore our Commodore CBM 8296; it was working some years ago but suddendly stopped working.

I suspect the PLA chips UE5 and UE6, I measure weird TTL levels on them so I'm changing them as explained on http://www.vic20.de/html/eprom_pla_8296_und_c64.html

But my problem is the weird daughter board sat in UE7; it contains 4 roms, marked 901465, from 20 to 23.

I can only find a single .bin file containing all 4 roms together on zimmers.net, but I can't find anywhere an explanation on how to change this daughter board with a single EPROM; what kind of eprom can be fitted into UE7? And how to connect this EPROM? Is the same schematics as UA5 and UA6?

Thank you for any help,

asbesto · Post by **asbesto** » Thu Feb 16, 2012 11:01 am

...also the schematics and info on that German page is very confusing!

Can anyone help also with that?

fachat · Post by **fachat** » Sat Feb 18, 2012 8:12 pm

Hallo, I hope I can help.

This is the first time I hear of such a daughter-board but I can understand its purpose. With the 8296 Commodore combined the previously used 4k ROMs into a single 16k ROM. The original 8296 comes with such a single chip in UE7. In your case some seems to have replaced the single chip with an adapter to use the original 4k ROMs.

So do you suspect these ROMs or the adapter to be defect? Then you have two options - use a single 16k ROM (assumingly with an appropriate pinout adapter if necessary, not sure about that), or replace/use the adapter with single 4k ROM chips.

Anything about PETs:
http://www.zimmers.net/anonftp/pub/cbm/pet/index.html
8296 schematics:
http://www.zimmers.net/anonftp/pub/cbm/ ... index.html
PET firmware (with 8296 specific firmware - e.g. for the PALs) in its own subfolder:
http://www.zimmers.net/anonftp/pub/cbm/ ... index.html

Hope that helps
André

asbesto · Post by **asbesto** » Mon Feb 20, 2012 8:58 am

Thank you, this just confirm my thoughts

Well, I fixed my 8296 just replacing UE5 with an EPROM using an handwired adaptor, but i'm just collecting information in case of a new failure

This daughter board was very weird to me.

A picture of that board is here:

http://museo.freaknet.org/index.php/Commodore_CBM_8296

Thank you!

fachat · Post by **fachat** » Mon Feb 20, 2012 8:17 pm

Interesting - the adapter looks original Commodore, except for the handwritten part number on the PCB :-)

But that confirms my suspicion, it is an adapter to use the original 4k ROMs in the 16k ROM socket of the 8296

André

fachat · Post by **fachat** » Mon Feb 20, 2012 8:26 pm

BTW, there is a little mistake on the description of the 8296 on your web site.

The 8296 is compatible with the 8096, which is just a 8032 with a 64k RAM board, so 32K+64K would be correct for a 8096.

The 8296, however, has 128k RAM. On the other hand, only slightly more than the 32K+64K of the 8096 can be used: The system ROM can be replaced with some of the extra 32k RAM using some board (jumper) configuration.

Some details can be seen in the 8296 supplement to the 8032 manual
http://www.6502.org/users/andre/petinde ... ement.html

André

Edit: some more info: http://www.6502.org/users/andre/petindex/8x96.html

asbesto · Post by **asbesto** » Thu Feb 23, 2012 11:04 am

Thank you for this, we fixed that page with the new informations!

Please excuse us for errors in pages, we're starting our serious work; we had very hard years in which we only stored our pieces in some deposits, and we decided to rent a space for our Museum only some months ago; so we really have a lot of voluntary work to fix everything: the space, computers, the internet sites and so on...

BigDumbDinosaur · Post by **BigDumbDinosaur** » Thu Feb 23, 2012 10:53 pm

Gee...and to think that I can recall when one could see these machines being used in businesses before IBM PCs ruined everything. Great that you were able to get it going again.