thanks to the magic of the 16822 logic analyzer trigger...

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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.

Like 27 Feb 2023 at 0:18 | Open on mastodon.social

18 comments

bitsavers.org

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

27 Feb 2023 at 0:38 | Open on oldbytes.space

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)

27 Feb 2023 at 0:52 | Open on mastodon.social

Tube🍂Time

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

27 Feb 2023 at 1:03 | Open on mastodon.social

Tube🍂Time

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

27 Feb 2023 at 1:14 | Open on mastodon.social

Tube🍂Time

replaced the inverter.

27 Feb 2023 at 1:25 | Open on mastodon.social

Tube🍂Time replied to Tube🍂Time

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

27 Feb 2023 at 1:25 | Open on mastodon.social

Sergio Aguayo replied to Tube🍂Time

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

27 Feb 2023 at 3:08 | Open on cs.social

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.

27 Feb 2023 at 4:41 | Open on mastodon.social

Tube🍂Time replied to Tube🍂Time

another day, another dead SYM-1.

7 Mar 2023 at 15:49 | Open on mastodon.social

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

7 Mar 2023 at 16:10 | Open on mastodon.social

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!

7 Mar 2023 at 16:20 | Open on mastodon.social

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.