Discussion about the Korg PolySix synthesizer

I would not assume the TC5514APL3 is bad. This is the memory chip and is
unlikely to affect the switch functions. It is also quite a bit more
expensive than the other chips. Without an oscilloscope or logic probe of
some kind to find the source of the problem, you could be replacing a bunch
of good chips trying to find the problem, only to find out that it was
another bad trace on the circuit board, not a bad chip. Use only TC5514APL3
to replace this if necessary.

 

The 1408 is the Digital to Analog converter, and also seems unlikely to be
the problem. Any DAC08 type chip can probably be used here.

 

The 14042 used for IC28, 29, 34, 35 are a 4042 Quad Clocked D-latch, and are
a prime suspect, although chances are the real problem is one of the D0-D7
traces leading to these chips, not the chip itself. IC28 handles the octave
and waveform, IC29 handles the subosc switch and sends the MG VCO/VCF/VCA
control signal, IC34 handles Phase/Chorus etc. and IC35 handles VCA
Attenuator.

 

Since you have multiple problems spanning all of these chips, it is unlikely
that all 4042 chips are bad. More likely there is still a bad trace
somewhere on the D0-D7 lines. If you are going to try to do this with only a
Volt/Ohm meter, then turn the power off and measure resistance from CN10 to
each of the connected chips for each of the D0-D7 signals. That’s a lot of
work but a bad data signal on one of these traces is likely the only thing
that could cause all of your problems.

 

Maybe it is time to invest in an old used oscilloscope. Since the clock
speed on a Polysix is only 6Mhz and most signals are well below that speed,
just about any old oscilloscope will work just fine. If you have an IPad or
IPhone it might be possible to get a cheap oscilloscope app for them. You
really need to be able to see what you are doing instead of working blind.

 

Don Backshall

 

  _____  

From: PolySix@yahoogroups.com [mailto:PolySix@yahoogroups.com] On Behalf Of
troels jørgensen
Sent: Friday, May 18, 2012 6:51 AM
To: PolySix@yahoogroups.com
Subject: [PolySix] Replacement IC's

 

  

Yesterday i changed IC28 and IC 31 - as far as i can see these have to do
with octave switch and waveform select (D00-D03) - and they still dont work
(along with pwm etc).

If i follow the signal chain my next guess would be that either IC32
(TC5514APL3) or IC33 (1408) is broken since they are the only ones that
have to do with the broken parameters, and they are the only ones that are
"after" what i have repaired in the signal chain.

-What would be good substitues for IC32 (TC5514) - IC 33 (1408) and IC 33
(14042)?

Thanks again everyone!

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