INSTALLED .1 UF CAPACITOR ON CARD AND REINSTALLED IN 1130
I grabbed a .1 uF capacitor with a 50V rating and soldered it onto the SLT card in place of the IBM part that snapped off. It was then reinserted into the compartment and worked fine.
BIT 7 DETECTED ON READS WHERE BIT 14 OF ADDRESS IS A 1
I noticed as I stepped through attempting to read sequential addresses that bit 7 would flip on for any read where the address had bit 14 turned on. Never when it was off.
ODD BEHAVIOR OF +READ CYCLE SIGNAL (OR MY RIGOL SCOPE)
I was triggering on the +Read Cycle signal, watching the Strobe and the differential ends of the sense wires. when suddenly the +Read Cycle signal began wobbling like AC inducted noise on an open wire. I did a continuity check from the originating gate over in compartment B-A1 all the way to the destination in B-C1 where I was measuring it, which proved it was good.
I turned the scope back and and got a few good traces, then the wobbly noise returned. At this point I had to leave, but I am not sure what is going on with the memory.
There is no point spending money on parts to restore the disk drive, typewriter or cosmetic features of the 1130 if something is fundamentally wrong with the memory. I have to get to the bottom of this and satisfy myself that the machine is restorable in order to move ahead on those other aspects of the restoration.
WORRISOME POSSIBILITY MENTIONED IN 1130 MAINTENANCE MANUAL
The manual mentions defects that arise in 1130 core memories where a relative short appears between sense wires and drive wires. This happens on the bottom board of the core memory stack and is generally not considered field repairable. The coupling of bit 7 turning on when address bit 14 is on does match that scenario.
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