[sdiy] OBXa Memory problems
montalbanogm at gmail.com
Thu Mar 5 19:11:55 CET 2020
I'm currently dealing with an OBXa that was working, but is now
exhibiting memory problems.
The ADC is working: all switches & pots can be used to set a patch.
Holding down Write & selecting a patch location will let the patch play,
but as soon as the patch is reselected or another patch is selected, all
patch data goes back to random.
Some givens: all power rails are clean and correct; all address & data
lines are present; ROMs, RAM and CPU have been swapped out with no
change. This unit is one of the early upgrades, with the piggyback
memory board, running version XAC0 in 2716 ROMs.
Since all ICs are socketed, I swapped out A117 and A115 and tested the
memory protect switch -- switch grounds A117 pin 1 as it should when
engaged, and releases ground when turned off.
I have the feeling I'm missing something stupidly obvious here, and
would appreciate any pointers as to where I can look next.
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