The Gottlieb System 80 CPU boards used in virtually all System 80 and 80A machines can be successfully modified to use 2532 EPROMs in place of the 2332A masked ROMs at locations U2 and U3 on the CPU board, with a little skill and the resources required to program these EPROMs. This modification was achieved using Texas Instruments’ TMS2532 EPROM and has not (as yet) been tested using the TMS2532A or other variants of the 2532. Users are cautioned to affirm pin assignments when attempting to use other 2532s other than Texas Instruments TMS2532. An Adobe Acrobat file of the Texas Instruments datasheet for the TMS2532 is available here.

An unmodified Gottlieb System 80 or 80A CPU requires that pins 20 and 21 of the 2332s located at U2 and U3 both be a logical high or ‘1’ to access the data on either U2 and U3 and gate it onto the data bus to the CPU. Modifying the CPU board to use the TMS2532 requires that both signals be combined together and inverted due to the fact that the TMS2532 uses essentially only one pin to achieve the same effect, and this signal must be an active low to access the data. Additionally, the pin assignments for the chip select and output enable on the TMS2532 are different than the 2332 masked ROM pin assignments, and some traces on the component side of the board must be cut and jumpered. A word of caution here: those folks who have the early version of the Gottlieb System 80 CPU (DET PB03-D102) should perform the conversion to use the 2716 game PROM first!

To modify the CPU board, several traces must be cut. These traces are all located on the component side of the board, with some appearances on the non-component side as well. Ideally, one should verify that the traces to be cut have continuity and are all present and undamaged before attempting this modification. I decided to make all the trace cuts (except for one) on the component side of the board so that I could revert back to the original board configuration by just tying the cut traces back together with wire wrap. You may choose to do this mod differently...

Schematic showing the modifications to be made
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Verify that the trace that carries the address bus 13 signal (BAB13) has continuity between U2 pin 20, U3 pin 20, and Z10 pin 6. Verify that the trace that carries the address bus 12 signal (BAB12) has continuity between U3 pin 21 and Z10 pin 12. Verify that the trace that carries the address bus 12/ (inverted) signal (BAB12/) has continuity between U2 pin 21 and Z7 pin 10. If these all test OK, we are ready to start hacking the board!

First, make sure that you install 24 pin machine tool sockets (preferred) at locations U2 and U3 on the CPU board. If you already have ROMs in these sockets, remove and save them.

Cut the trace that carries address bus signal BAB13 to U2 pin 20 and U3 pin 20. This trace MUST be cut in two separate places due to the fact that both U2 and U3 pin 20 are connected together on a single trace. The first cut (for U2 pin 20) should be on the trace that appears between pins 5 and 6 of U2 on the component side of the board as shown in the photo below. The jumpers come later.

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Verify that there is NO continuity between Z10 pin 6 and U2 pin 20. OK? Good! Verify that there IS continuity between U2 pin 20 and U3 pin 20. OK? Good! Now we can cut the trace that connects them both together.

Cut the trace that connects U2 pin 20 to U3 pin 20. This trace comes directly off of U2 pin 20, so there should be no problem locating it.

Verify NO continuity between U2 pin 20 and U3 pin 20. Now that we have taken care of the trace that carries signal BAB13, we can go on to the others.

Cut the trace that carries signal BAB12 to U3 pin 21 as shown above. 

Cut the trace that carries signal BAB12/ to U2 pin 21 as shown above. This trace appears between pins 4 and 5 of U2.

On the non-component side of the board, cut the trace leading to pin 21 of U3 and jumper pin 24 (+5VDC) to pin 21.

On the non-component side of the board, jumper pin 24 (+5VDC) to pin 21 of U2.

OK! All the trace cuts are complete, and we have tied pins 21 of U2 and U3 to a high logic level (once the board is powered up, that is). 

Now, the hard part. We have to combine signal BAB13 with BAB12, and also have to combine BAB13 with BAB12/. How to do this? Well, we have two spare gates that we’re going to use to combine both signals, and then invert them so they can be used with the TMS2532’s. Fortunately, we have two spare gates at Z9, a 7400 NAND gate. OK so far? Good. 

Remember this? Yep, it’s the first trace cut we made. Solder a jumper to the LEFT side of the cut trace and connect this trace to Z9 pins 9 and 12. This will provide the BAB13 input to each one of the spare gates.

OK. Now we’re at the trace we cut in step 3. On the LEFT side of the cut trace, solder a jumper as shown above and connect it to Z9 pin 13. This connects the BAB12 signal to the other input of one of the spare gates. At this stage, we have completed both BAB12 and BAB13 inputs to one of the spare gates.

On the LEFT side of the trace we cut in step 4, solder a jumper and connect it to Z9 pin 10. This completes both signal inputs BAB13 and BAB12/ to the other spare gate. Now we have to connect the outputs of Z9 to each one of the 2532’s.

On the RIGHT side of the trace we cut in step 1, solder a jumper wire and connect it to Z9 pin 8. This is the output of the combined and inverted signals BAB13 and BAB12/, and we are connecting it to U2 pin 20. 

On the RIGHT side of the trace we cut in step 2, solder a jumper wire and connect it to Z9 pin 11. This is the output of the combined and inverted signals BAB13 and BAB12, and we are connecting it to U3 pin 20. 


Here is a photo of the mess we created at Z9.

Well, we’ve just completed hacking the board to use TMS2532 EPROMs in place of the 2332 masked ROMs. Now you should verify that everything works. 

Just for fun, here’s a photo of the whole mess.