Good call @MarAlb, you could be onto something. The NVRAM is the MK48Z02B-20 chip next to the EPROM, datasheet says pin 21 on the MK48Z02B-20 is the the R/W pin.
BTW it's most likely the internal battery in the NVRAM has now extinguished being 33 years old.

MarAlb gave you a pretty good starting point and it's worth the few minutes to check. To elaborate:

Here's the pinouts for the 6802/6808 CPU plus the 27128 EPROM and the MK48Z02B NVRAM on your board.
Do some continuity checks from the 40 pin chip pins 33 - 26 (which may be data lines) and see if they connect to the corresponding data pins at the EPROM. Check some of the lower address lines between the 40 pin chip and the EPROM for continuity too. See if the crystal is connected to pins 38 and 39 of the 40 pin chip, and also check if the ground (VSS) / 5V (VCC) pins match the below.

That Delco chip just might be a rebranded Motorola 6802/6808 CPU. It has the typical Motorola plastic package dimples from that era.

BTW the black electrolytic capacitor in the middle of the board looks like it's bulging. I'd be weary of other chips being fried considering the Delta chip is getting hot and the regulator has previously gone up in flames.

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