As some might recall I found I had a bad Standard RM module on a Model 100 I am refurbishing. Luckily the machine had two option RAM modules, so I was to get it working again. I noticed in the Tech Ref manual that the RAM module schematic was included. This led me to test my bad module and figure out which chip was in the address range where the stack was being overwritten and which chip on the module that was.
I then ohmed out that chip and found that the internal traces on the module are good so the chip must be faulty. The Standard RAM module has Toshiba TC5518BF-25 and the Option RAM modules I have use a Hitachi HM6117LFP-4. Of course, the only place you can seem to find them is from eBay and I am very hesitant to buy ICs from eBay especially from China (who knows what you really get.) But if I could pick up a replacement chip for less then $10 and repair this RAM module it would be worth it perhaps. The Hitachi parts seem to be the best option and I don't see an issue with mixing them with the Toshiba on the same module as each chip is accessed individually (not 1 bit per chip) so timing should not be an issue. Has anyone done this before. Any eBay sellers you have dealt with before when buying these old static RAM chips? Thanks, Jeff
