How to upgrade
your Multipak

HOW TO

Quick Instructions for
Multipak Model 26-3024
or Reproduction Equivalent

You have a chip ready to install. Use these steps if the GAL chip is socketed on the board.

1. Remove the screws and gain access to the board inside the Multipak.
2. Find the chip on the board.
3. Note its orientation.
4. Remove it from the socket.
5. Replace it with the new chip oriented in the same direction as the original chip (there is a notch on the chip). Take care to ensure the pins are all correctly seated in the socket.
6. Reassemble the Multipak.

SUPPORTED

Which Multipaks this covers

Tandy made two families of Multi-Pak Interface. Only the earlier 26-3024 uses a drop-in GAL at U8, which is the chip our firmware is built for. 8BITCRUSH Multipaks are reproductions of that 26-3024 board, with U8 already in a socket.

FILES

The GAL chip

If your HDMI Cart came with a programmed GAL, skip the programming step and fit that chip if the GAL chip is socketed on the board. To program your own, download the JED files from Firmware on GitHub and write a GAL16V8 or ATF16V8B with a TL866, minipro, or similar. Use the same package as the chip you remove: 20-pin DIP on an original Tandy 26-3024, PLCC-20 on an 8BITCRUSH Multipak.

• CoCo 1 or 2: mpi_coco12_stock.jed. Use mpi_coco12_sniffer.jed if the HDMI Cart will live in the Multipak.
• CoCo 3: mpi_coco3_stock.jed. Use mpi_coco3_sniffer.jed if the HDMI Cart will live in the Multipak.

The sniffer images let a listen-only cart such as the HDMI Cart see the data bus through the Multipak. Stock images are the usual CoCo 3 (or CoCo 1,2) Multipak decoder with no extra enable on writes.

IN DETAIL

Change the GAL on the motherboard

Fit the programmed GAL you already have — including one supplied with an HDMI Cart — or a chip you programmed from the files above, if the GAL chip is socketed on the board.

1. Turn the Colour Computer off. Unplug the Multipak from the cartridge port and from power. Remove every cartridge.
2. Open the case. On an 8BITCRUSH Multipak, lift the 3D-printed lid. On an original Tandy 26-3024, remove the case screws and lift the cover.
3. Find U8, the 20-pin PAL or GAL. Original Tandy boards ship with a PAL14L4, often soldered; some silkscreens say U6. 8BITCRUSH boards already have a GAL16V8 in a PLCC-20 socket at U8.
4. On an 8BITCRUSH Multipak, lift the GAL from the socket and press the programmed chip in, matching pin 1.
5. On an original 26-3024, pull the PAL if it is socketed. If it is soldered, desolder it and fit a 20-pin DIP socket, then insert the programmed GAL with pin 1 to pin 1. Keep the old chip.
6. Close the case. Reconnect power and the cartridge cable with the computer still off, then power on.

This is a DIY chip swap if the GAL chip is socketed on the board. We cannot work on a Multipak you already own. Keep the stock chip so you can restore the board.