Gregory's ServerU9 pin 11, aka Memory Write Protect#, measures 30 ohms to ground. this is suspicious.
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15 comments
 @tubetime What would've been the purpose of the MM to 45 jumper then? @sergioaguayogr the memory in the 6532 is used as a vector table. it's nice to protect it from accidental modification by a runaway program, so MM to 45 is a write protect function. seems to be a similar issue. when it tries to jump to outvec+1 (previously stored in the 6532's RAM) it goes to 0000 instead of the actual character output routine pin 11 of this inverter is shorted to ground. this is the exact same problem as the last SYM-1! so strange. different manufacturers and exactly the same failure (~20 ohm short from pin 11 to ground). must be damage caused by something the last owner did.  woot! |
sure enough, bad inverter. looks like it was bad back in the day--someone removed the MM to 45 jumper.