this is an indirect jump to the console output routine....

this is an indirect jump to the console output routine. it's supposed to beep. but it's jumping to 0000! on initial boot, A600 etc is supposed to alias to 8F80 which is in ROM.

Like 26 Feb 2023 at 23:39 | Open on mastodon.social

20 comments

Tube🍂Time

the jump table is getting copied into the 6532 RIOT but the write is getting corrupted. it's supposed to be '89' but something else is trying to drive the bus at the same time

27 Feb 2023 at 0:16 | Open on mastodon.social

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.

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

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.