This is a board which plugs into the 6502 CPU socket of Commodore PET computers. By use of the DIP switches you can select to replace the onboard ROM or RAM of the PET computer. The original CPU plugs into this board, or optionally, it can be supplied with a tested replacement 6502 CPU with the board. The board has 32K of RAM and a ROM chip with a select of PET ROM sets.
This board has three uses:
If you Commodore PET has a memory fault or a ROM fault, often resulting in a screen of random characters on early PETs, or a black screen on later models, you can use this to bypass the faulty ROM or RAM chips and get the PET running again.
If your PET has 8K or 16K, you can use this board to upgrade to the full 32K of RAM. If you have the original BASIC 1, you can upgrade to the bugfixed BASIC 2, or get more functionality with BASIC 4. As with the replacement option, you can then remove the original ROM and RAM (if socketed) to reduce power consumption of the PET.
If you have a non working PET, you can find out if the fault is ROM or RAM, and with the larger board, you can isolate this down to find out which ROM or bank of RAM is faulty.
There are two size boards:
The smaller board is ideal for plug in and go replacements. 5 DIP switches control operation:
The original larger board has more options for narrowing down a particular faulty ROM. There is also a LED which flashes for write activity, so you can see if the PET is alive and doing things. This board has 9 DIP switches:
There are various choices, depending on which machine(s) you have. These include the three versions of BASIC, and a PET Tester ROM which alternates between a character set display and a test of the first 1K of RAM.
This is suitable for the original 2001 and 2001N series with normal/graphic keyboards (4 40 pin chips, no 6545) - 3008/3016/3032/4016/4032 with 9" screens
This is suitable for 12" screen PETs with CRTC chips (a 6545 as part of 5 40 pin chips in a row) - 4016/4032/8032
Both of the above.
Some of the early 2001 models have usual IC sockets which are U shaped with high sides. The IC sits down lower inside the socket (see the last photos above). Most plug in boards do not fit in these sockets. I have a special build with long thin pins suitable for these type of sockets only. The long thing pins are tricky to use on normal sockets as fitted on 95% of PETs, so this is only if your socket is not a standard flat profile.
Optionally, I can include a tested 6502 CPU. Currently these are new old stock R6502P chips.
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I write a blog about old computers, repairing them, upgrading them, replacing them. Read more at blog.tynemouthsoftware.co.uk