Discussion about the Korg PolySix synthesizer

At 10:55 AM 11/9/2007, you wrote:

>does anyone know what IC 31... on board klm-367 does? it would be the
>first chip to be damaged from the acid leak....it is a 74LS08 type
>chip. readily available from Digikey, but I really would like to know
>what functions it controls. this info might help explain my polysix's
>odd behavior after battery leakage rather than just blaming the traces.

Look at the schematic (and by the way, it's pretty much impossible to 
achieve any successful repairs on the P6 without referring to the 
schematics) -- ICs 31 & 30 are quad AND gates, basically serving to 
buffer the eight data lines between the CPU chip and the rest of the 
circuitry.  Each of these lines is crucial to the correct performance 
of the synth; if any one is missing or shorted, it can cause any 
number of malfunctions of the front panel, memory, patch control voltages, etc.
Also note that each data line connects to numerous points on the 
board;  even if most of them are good, having only one missing can 
still cause havoc.

The easiest way to observe all this is with a scope;  referring to 
the schematic, view each line starting at the CPU & continuing to the 
IC30 (or 31) input, then from the IC30 or 31 output to the other 
indicated points.  Any bad or missing signal should be immediately obvious.
Note that the 4042 latch "IC34" on  the schematics is labelled 
incorrectly;  it should be IC24.

The lengthier process is to use your meter in continuity mode (this, 
of course, is done with the power off);  check for proper  continuity 
for each data and address line (for example, pin 12 of the CPU should 
connect to pin 4 of IC 31 and to pin 14 of the RAM chip;  pin 6 of IC 
31 should connect to IC26 pin 13, to connector CN06 pin 3, IC28 pin 
4, etc etc etc).

It sometimes happens that IC31 (or one of the other CMOS chips in the 
battery leak area) is indeed dead;  but the most frequent cause of 
nonfunction is a bad circuit trace.

~GMM
(repairing battery-damaged PolySixes for longer than I'd care to think about)


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