I've got a Super Pac-Man motherboard giving a RAM 5 error. Ram 5 is the 2148 at location 3K. It's good, as is the 2148 at 3L. All the address/data lines are pulsing away on both the RAMs. Here's what I've found....all ROMs are good, all Proms are good, both processors are good, all customs are good, a lot of the suspected sockets have been replaced. The sound processor at 1L isn't "turning on". The reset pin (#37) is stuck low. The schematics label this "subreset". This signal comes from the LS259 at location 2M. All of 2M's outputs are stuck low. All the inputs look good. I replaced it...no change. None of the outputs are shorted to anything "low". Other abnormalities....The main processor at 1A has pin 23 (MA15) stuck high. It should be pulsing. It's not shorted to anything "high". Everything at this processor looks good. This MA15 signal feeds the PROM at 2B. A lot of the outputs of this PROM are stuck high (none are shorted to "high")....I assume because of the bad MA15 signal. These outputs of this PROM are screwing up the LS254's at 1F, 2F, and 2K causing all of these to "isolate" their buses. Needless to say, all of this is sending me around in a big looping circle. I have replaced and/or checked a lot of these chips in the "circle". If anyone is not totally confused by this mess....any suggestions is appreciated. Anyone want to school me on a LS259. What am I missing on that 2M location. I don't quite "grasp" the datasheet on that bugger.
Big thanks!
Edward
Big thanks!
Edward


