What is it?

This is a drop in replacement motherboard for a Commodore PET, supporting 40 and 80 columns and 32K RAM and a choice of BASIC versions, including it's own Mini PET BASIC V4.1, which adds a DOS wedge, extended machine code monitor, self test and a built in file browser.

Why did you make it?

It can be difficult to keep an original PET motherboard running, with the vintage ROM, RAM and IO chips. This replacement uses all modern low power parts and is a fraction of the size, but lines up with the rear ports and mounting holes.

What makes it special?

This version can support 40 and 80 column video modes, so can replace a 40xx or 80xx PET board, but can also give the option of easily switching between modes.

The board is powered by the PETs original power supply, either 9 pin on 2001N and 40xx and 80xx models, or 5 pin on the original 2001. Alternatively, and for testing purposes, 9V DC can be supplied by a 2.1mm DC jack.

The board can drive PET 9" and 12" monitors at 50 or 60Hz. It can also optionally generate a composite video output (but not at the same time as driving a 12" monitor).

There are various ROM versions which can support the chiclet / normal / graphics keyboard, as well as the business keyboard. There is no support for a VIC20 or C64 keyboard.

I did have a version of this was was designed for standalone use with it's own keyboard. I don't have any of those left at the moment, but if there is any interested, I can get some more of those.

Like the later PETs, there is a piezo sounder which will make the power on chirp sound and dound in games such as Space Invaders, Tut-Tut and Cheese and Onion.

IO is provided by the same ports as the original Commodore PET

• IEEE-488 - supported external disk drives (or modern replacements such as my SD2PET - https://www.tfw8b.com/product/sd2pet-commodore-pet/ )
• Userport - Parallel IO for joystick or serial. As with the PET this has no power and is only partially compatible with the VIC20 or C64 userport.
• Datasette - Two ports (one rear, one side) for Commodore 1530/C2N datasettes

The CPU is a modern WD65C02S, this is not pin compatible with the original 6502, so devices that plugged into the CPU socket cannot be used (no 64K RAM boards or Super PETs)

The Mini PET 40/80 Internal can directly replace the mainboard in the following machines:

• PET 2001
• PET 2001N / 2001B
• PET 2008/2016/2032/3008/3016/3032/4008/4016/4032 with 9" monitor
• PET / CBM 4016/4032/8032 with 12" monitor

It can be used with the 8096, but the 64K RAM board will not be used, so it will function as an 8032.

It can be made to fit the 8032-SK or 8096-SK, but the keyboard cable will need to be extended.

It is not suitable for an 8296-SK or CBM-II series or SuperPET.

Options

The current PCBs are the prototype version and contain an error which needs to be fixed with a small modification. For that reason, this is not available as a kit, only assembled (and with the modification fitted)

Sockets are provided for the larger ICs, but are optional for the smaller logic ICs.

If fitting this into a PET 2001 with the internal datasette, an extra connector can be supplied that will allow this to be connected internally to port 1 as it was originally. (port 1 on the rear can still be used to power an SD2PET etc.)

The board can also be installed deeper into the case, to allow something like an SD2PET to be installed internally, instead of poking out the back.

Some of the photos show older versions of the board, but the version supplied is the Mini PET 40/80 Internal V1.82B.

No PET case, monitors, keyboards, SD2PET, datasettes or case dust are included, only the Mini PET 40/80 board and mounting pillars.