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Tube🍂Time

thanks to the magic of the 16822 logic analyzer trigger output, I can see that the 6532's R/W# never gets driven low.

18 comments
bitsavers.org

@tubetime
I should see if we have the schematic and run it through the blueprint scanner

William D. Jones

@tubetime If I had enough $, I'd design a Super-RIIOT IC (SPI Ultra Precision Extra ROM ROM I2C I/O Timer... acronym needs work)

Tube🍂Time

U9 pin 11, aka Memory Write Protect#, measures 30 ohms to ground. this is suspicious.

Tube🍂Time

sure enough, bad inverter. looks like it was bad back in the day--someone removed the MM to 45 jumper.

Tube🍂Time replied to Tube🍂Time

now it beeps and the display lights up! it's alive.

Sergio Aguayo replied to Tube🍂Time

@tubetime What would've been the purpose of the MM to 45 jumper then?

Tube🍂Time replied to Sergio

@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.

Tube🍂Time replied to Tube🍂Time

another day, another dead SYM-1.

Tube🍂Time replied to Tube🍂Time

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

Tube🍂Time replied to Tube🍂Time

pin 11 of this inverter is shorted to ground. this is the exact same problem as the last SYM-1!

Tube🍂Time replied to Tube🍂Time

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.

bitsavers.org replied to Tube🍂Time

@tubetime

woot!
at one point I had a SYM/KTM. The editior/assembler firmware is under bitsavers.org/pdf/synertek/sym

Joviko Wi replied to Tube🍂Time

@tubetime

Redid the sketchy solder on R83 too. Nice!

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