We tested and repaired the power supplies before powering up the circuit boards, to make sure we didn't fry anything.
Each of the four boards has 80 memory chips. These are 4116 DRAM chips, each holding 16 kilobits. Each board holds 128K 10-bit-wide "chunks". Data is stored as 32 bits + 8 bits (actually 7) of Hamming error correction and parity.
The issue is not when you powered up the machine and the ram boards, its more whoever powered them up before you got the machine.
That power supply may have failed decades ago. Was the machine known working when it was last powered up?
Is there any way you could build a rig to test each 4116 chip, or a rig you could plug each board into which would supply proper voltages (in the correct bring-up and bring-down order, because 4116 drams are weird like that) for the dram, and do a pattern test on the entire board all at once?
Personally I don't like 4116 drams at all because they're very unreliable. (4164s are far superior in this regard.) See the PARC notes on bitsavers re: the notetaker project, the notetaker test systems were frequently out of commission due to failed 4116 dram chips, or running with one or more chips dead and the ECC constantly correcting the errors.
Each of the four boards has 80 memory chips. These are 4116 DRAM chips, each holding 16 kilobits. Each board holds 128K 10-bit-wide "chunks". Data is stored as 32 bits + 8 bits (actually 7) of Hamming error correction and parity.