These lines are used as sort of a memory page selector by the CPU. The other SRAM address lines are accessed through latch U17 (Schematic p2) and the 16 bit data lines with latches U16 and U30 (Schematic p2), all controlled by the CPU. When switching presets these latches are clocked. Some presets seems to continuously activate these latches, probably to write expression pedal data (Midi) into the DSP memory (not investigated). When I lift these latches, the tone is gone. However it may simply be that the SRAM data is zero'ed out and that this will simply not generate a tone. Reinserting the latches brought back the problem (of course). One thing I don't understand is the XENEX signal that seems to give the CPU access to the SRAM. However, I can find no way how the CPU manipulates this signal. It is connected to the DSP ENEX pin 81 (schematic p1) though. If I had to guess I would put my money on the DRAMs and replace them all. They get the warmest -not hot exactly, you can still touch them, but warmer than I would like. I also noticed after having the unit on for a while (like an hour or so), that the little transformer gets warm and the voltage regulators (+5/+12/-12) also get warm. So perhaps something is drawing more than it should? Thanx for reading.
So finally the DRAM memory I ordered came in this week and I have tried it today. After staring at the schematic for a couple of minutes it dawned on me that perhaps it was just sampling garbage on the inputs.? I started to look for the ADC but couldn't find any.
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