The preservation of the Prodigy Chess computer

I really like chess computers but usually they are too integrated to easily preserve so they kind of piled up in the garage: A Boris Diplomat, already preserved by Sean Riddle, a Mephisto Mini and a Mephisto Tutor among others. However this time I bid for an ACI Destiny Prodigy and got it!

The first thing to do in order to preserve an old MCU design is to check if anyone has done it before or if there are pictures of the inside already. I found plenty of information of this classic but no emulation in MAME or elsewhere easily found. Great, lets do it!

Among all the information on the net I found pictures of the PCB revealing it has a very discrete design, that is it uses a 6502 with external RAM and ROM chips that are easily accessible. So carefully I opened the chess computer revealing the PCB. Here I stumbled on the first issues, the RAM and ROM were not of brands I already knew:

The RAM is a Mitsubishi M58725P which I didn't recognize but a quick Google revealed that it is pin compatible with a standard 6116 2KB static RAM. So far so good. The ROM however, a Rockwell R2912, has no information easily available on Internet. The chess sites mentions that the ROM is 8KB but that would require more pins than the 24 shown in the pictures. I also saw that the pictures showed a R2907 so the information can refer to 8Kbit aka 1KB x 8 bits. EDIT: But didn't!

Interestingly enough the PCB from the net had other RAM and ROM brand, so my PCB was clearly a newer revision than the pictured one found on the Internet. Since I had no data sheet available the next step is to follow the traces and see if I can figure out what they are. This is done by a simple beeper:

I verified that all the pins were connected to the data or address bus according to the 24 pin 2716, which was my suspect and they were except for pin 18 (*OE), 20(*CE) and 21(VPP). Now the only danger I could think of was if the device required negative voltage which my ROM reader doesn't supply and which also in some cases are very destructive for the device if not supplied according to the datasheet.

I was looking carefully for circuits that could generate a negative voltage from batteries but none were found if it was even possible at the time to a cost suitable for a consumer grade product. I didn't think so and put the ROM into the ROM reader which happily read the ROM as a 2716!

Now starts the work of figuring out the inner secrets of the Prodigy hidden in the PCB and revealed by the ROM code. I will collect all info I find on my Prodigy page, stay tuned! Next-->