[sdiy] Prophet-5 help?

Eric Frampton eric at ericframpton.com
Thu Sep 19 01:18:34 CEST 2019

I’m (still) working on this rev 3.0 Prophet-5 (ugh) and have managed to back myself into a corner.

I put the Retrolinear replacement PSU in there with their Memory Watchdog controller chiclet; those parts are working fine.
I’ve done the 2716 EPROM mod and installed some v.8.2 ROMs.

The unit seems to be working correctly except for one major issue: Since doing the 2716 mod and installing the new firmware, now whenever I got to record a patch, the unit doesn’t exit Record mode (also, the LED never extinguishes) and the patch isn’t written. Unfortunately, because the other mods are done, I can’t backtrack to the 2708’s.

If I hit Record+Load, the unit *does* seem to drop into Cassette Load mode, so I think the front panel logic is OK.

I can see expected changes at both U320 and U323 when I move the back panel Rec Enable switch
I can see active data and address lines on all RAM and EPROMs
I’ve tried pulling individual RAM IC’s
I’ve tried pulling NVRAM IC’s and swapping them with spares

I’m not seeing any change on pin 5 (A15) of the CPU, which is one input of the gate whose output is U320:11.



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