[sdiy] Polysix - trouble with EG Mode

Dave Magnuson resfreq at hoohahrecords.com
Fri Jun 28 22:23:47 CEST 2002

Thanks Old Crow, 

comments inline...

At 04:09 PM 6/28/02 -0400, The Old Crow wrote:
>On Fri, 28 Jun 2002, Dave Magnuson wrote:
>> The VCAs seem to be stuck in "gate" mode, and won't respond to the envelope
>> generator.
>> I noticed TP5 on the KLM-367 (processor/battery) board is listed as "VCA
>> Mode" on the silkscreen.  When checking this with a DVM or oscilliscope I
>> see no change when flipping the switch...  that point always remains at 0V.
>  VCA mod(ulation) TP5 is to verify the MG output when MG->VCA is

Ok, thanks... the board is installed in the synth, so I couldn't see where
the traces go... I just saw "VCA mode" and assumed it was related

>> I'm guessing that IC34 (14042) on the KLM-367 is dead.  Does this seem
>> like the culprit to you PS6 gurus?
>  I'd check pin 3 on this IC to see if it changes state when the EG/gate 
>switch is moved.  Also check continuity from this IC pin to CN05-1 
>(connector 5, pin 1).  It is this signal that enables/disable ADSR action 
>on the VCAs.

Checking pin 3 of IC 34 with the scope reveals that it is normally high
with very quick negative going pulses (a few milliseconds long, about 20 or
30 mS apart).   Changing the switch doubles the frequency of the pulses.

I get the same signal in both sides of CN05-1 as I do directly at pin 3, so
the conncetion is good from the IC, across the jumper cable (CN05) and onto
the next board

Dave Magnuson

Resonant Frequency:
resfreq at hoohahrecords.com

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