*Please Note* This product requires the removal of an IC from the PCjr motherboard and the installation of a socket. Please read the entire description before purchasing.
The TandyMod is designed to realign the PCjr graphics memory to make it compatible with the Tandy 1000 video RAM structure. The Tandy 1000 was first designed as a clone of the PCjr and they made a bet that the platform would be very popular. However, IBM wound up discontinuing the PCjr after just a short time. Tandy did make a few modifications, like the addition of a standard ISA bus as well as a realignment of the video memory to make it more linear. Tandy may have cloned a dead platform, but it turned out to be popular enough on its own and lived on for many years after the PCjr was discontinued. Some games written specifically for the Tandy 1000 will not natively run on the PCjr without changing the way video memory is accessed, and that is exactly the purpose of the TandyMod.
We have known about the TandyMod for some time now, but only decided to release it once we released the Resound jr OPL3. It is a great companion for the TandyMod, as the Resound jr gives more audio options for the newly accessible games. The TandyMod has been around for several years in many different forms. It’s not clear where the original design came from, but the first iteration we located was designed by the same designer of the Jr IDE, Alan Hightower. Later iterations surfaced as well, but we used the form-factor designed by Charles Terra. See Chucks’ great IBM PCjr site here: IBM PC JR (pcjribm.com). Thanks Alan and Chuck! We really appreciate your contributions to the PCjr community!
The TandyMod does require installation on your PCjr motherboard. The traces are very thin on the PCjr and it is very easy to lift pads and traces from the board when removing parts. A single IC must be removed and replaced with a socket for the TandyMod. The IBM PCjr service manual shows this IC to be named ZM31. On page 517 (System Board B-19), you can locate ZM31 at coordinates D-8 on the sheet. The original IC is a 74LS157-type IC. The service manual is located here: PCjr_Technical_Reference_Nov83.pdf (archive.org)
IBM did not label the ICs on the motherboard, so the best way to locate the chip is to watch the video we made on the installation here:
In our video, I actually manage to lift a trace myself! It is much easier to do on this board than others I have worked on due to the very tiny pads. I highly recommend a good desoldering tool and a lot of patience if you decide to upgrade your PCjr.