On 9/8/19 3:20 PM, Noel Chiappa via cctalk wrote:
> From: Mister PDP> listed back there were numerous bad addresses all over memory. > ... > I cannot find schematics for any of the boards ..... With the completed chart in hand, given a failing word (address and bad data), you can work out which chip is at fault, and replace it. Repeat for all memory errors.
Noel's approach is valid and I have done the same on several boards. Sorry I don't recognize the vendor of your board.
I would also suggest checking the voltages on the board, especially the -5V for the memory chip if the memory faults are scattered across the memory space. The circuitry on the upper left of your picture is probably a NE555 that is used as a charge pump to generate Vbb from the LSI power supplies.
The larger capacitors are probably tantalum (Kemet?) and should have aged better than electrolytics of the period.
Jerry
