On Mon, 2009-06-15 at 23:32 +0000, crustypaul wrote:
> in the factory soundbank, but all i ever get out of the thing is
> filtered noise and no DCO tones. The noise source, envelopes, delay
> and filter are definately working but theres no DCO's.
Okay, either the DCOs aren't running or they are not making it out to
the filter. Note that I'm working from a Poly-800, not a Poly-800 Mk 2,
but most of the guts should be the same.
When you play a note, one of the little pairs of diodes in the row of
eight pairs that stick up should light. This feeds the VCA control
voltage for each oscillator to the MSM5232. It goes through one of the
notorious 4051 multiplexers. If you find there's a signal on pin 3 of
IC12 but not much on the outputs, you've got a dead multiplexer.
IC6 is a 4053 multiplexer, used to switch the square/saw outputs. Check
to see if pins 1, 2, 12 and 13 have any sort of signal when you play
notes. If not, guess what? Another stuffed mux.
The only other thing I can think of is that there's something amiss on
the digital side, and the MSM5232 is never seeing a /WR pulse from the
address decoder. That's going to be a flowery twat to diagnose without
an oscilloscope.
Gordon