Kevin- Are you putting VDD on the Rockwell MM78 test pin, or a different voltage? I got an MM75 as well as the MM76EL, and I'm not getting anything from either of them. I've tried several different voltages on VDD and the test pin.
These are MM78's and not the L version. they run on 15V (or -15V depending on your perspective). I connect ground to pins 4 and 6, then 15V to pin 7, and finally 12V (via a pot between ground/15V) to pin 8.
5 connects thru a 56K resistor to ground, clock goes into pin 3 at 15V swing levels, and there's another output at 15V levels driving reset. The 8 RIO lines are pulled to ground thru 22K resistors and that's where the data should appear.
1 byte per clock, starting at address 3C0h (reset vector) 4-5 bytes after reset.
I got 7 more games today, with a total of 9 CPUs inside. two games have dual CPUs (sound + game CPU). I have dumped 7 of these CPUs... one COP411, HD38820, HD38800 (two), D552C (two) and D553C.
Got a D1771-11 and D7528 which will be 'fun' to dump/RE. I am not sure if I can get them to dump but I will give it a try some time soon.
The D1771 is a bone of contention up to this point since not a single document about it to speak of has ever been found, just a patent and a few other scraps. The D7528 has no test pin so I will have to try and coax it into test mode by trying a few things like pulling pins above 5V thru a resistor and seeing if it has a protection diode or not. (no diode = likely test pin sometimes).
The ROM dump production line is really moving in full swing now. I have 18 games now using the HD388xx parts which we still need opcode bit docs for.