The Commodore 1551 disk drive used a custom cartridge to connect it to the Plus/4 and C16 computers. It only contains two chips, but one of those - the 6523 28 pin Tri-Port - is impossible to find. Even at ebay prices.

Fortunately, Commodore made two versions of the same chip. And the 6525 is identical internally, but comes in a 40 pin package. This 40 pin chip is used in multiple devices and consequently much easier to find.

The second chip is the 261641-03 address decoding PLA. This is easily obtained, but there is also an option to use an EPROM instead (code for this EPROM can be downloaded from zimmers.net). The PCB has sockets to use either an original PLA or an EPROM equivalent.

Because this cartridge is now longer than the original, I've made a 3D printed case to fit it (including a taller lid to cope with Dupont style connectors on the cable.

Components:

1 x MOS 6525 Tri-Port Adapter

Either: 1 x Suitable EPROM/EEPROM (e.g. Winbond 27C512)

Or: 1 x PLA 261641-03

1 x 2k2 Resistor

2 x 100nF capacitor

1 x 28 pin DIP socket

1 x 40 pin DIP socket

Cable tie, pin headers, as required

EPROM code for the PLA equivalent can be downloaded from http://www.zimmers.net/anonftp/pub/cbm/firmware/drives/new/1551/index.html

This is a tested and working circuit. See my YouTube videos:

and

(link will be added after release)