Repair or Replace? [Was: Repairing Timex]

Hi One method that has not been talked about too much is one that I've often used. It does take a prom programmer and an assembler helps. I often write small pieces of test code to check one part or another of a micro system and program an eprom with it. While I usually make an assembler for the processor I'm playing with, the code chunks are so small that one could easily hand assemble. ( Of course, if you just happen to have the right ICE or ROM-ICE, you don't need the programmer. Oh I wish!! ) I usually try to find some output someplace to use as a trigger or if you are luck, a display of some kind. Once one has some kind of basic indicator ( it can be as simple as a LED light ) one can systimatically test each part of the system. Some processors that have a lot of registers, like the Z80 can run without RAM, making RAM test without any system RAM used by the program. I use this method on old computers as well as on pinball machines ( an other hobby ). It helps to have schematics but if you understand the basic layout of the machine and have data books for some of the LSI I/O chips, it doesn't take long to write useful test code. Dwight