my Fatman got its brain confused

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my Fatman got its brain confused

Post by arsenlives »

So I was trying to add the cmos subharmonic generator mod to my fatman and it wasnt working properly, kind of in and out so i disconnected it and noticed my midi signals seem to be a bit confused now. The mod was tied in at ic14 voltage regulator for gnd and -12 v, both 555s pin 3, and ic17 lm13700s pin3 vcf in. What is odd is that now the midi seems to be a little scrambled with the mod removed. the first octave (c0 - 1) works fine but as you move up the scale and get to c#1 it plays a note equal in pitch to approx. a0. D1 is about a b0 in pitch and so on until you get to c#2 which jumps back to the pitch of c#2. Its as if all of octave 1 is transposed down 4 notes and only does this in octave 1. I dont think this is a 555 issue because both vcos do the same. Vcf seems to work fine. Could this be a voltage regulator issue? Its still reading -12 and -5 at its output/input. also just in case the 555s are swapped with cmos ones and i added and lee diode mod. also noticed that when i just barely touch the trimpot at r21 it jumps in pitch and rotating it in either direction doesnt produce a smooth pitch change like the other trimpots. theres nothing shorting physically on the trimpot but its behaving rather erratically. ill try to replace it but i think that its probably a result of a larger problem.
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Re: my Fatman got its brain confused

Post by PAiA-Scott »

Copied from the "sent" folder in response to this same message via email:

Hello Arsenlives.

It seems like the IC9 which works to divide the pitch cv according to the octave might not be getting the right voltage to it, or had an accidental short-circuit to it while the modification work was in progress?

Attached is a pdf with tests/checks including the power supply sections which should be checked at the IC9 too. The ground to pins 6 and 8 is through many jumper wires round and about the board back to the AG/AE/DG origin. Pin 7 gets the negative twelve volt supply through a couple of jumpers too. The positive dc supply is to pin 16 (again, towards the end of the line via jumpers). Maybe soldering to one of these pulled it up away from one end or the other, opening the link to the supply or ground???

Thanks. --Scott

ps The trouble-shooting tips/suggestions pdf was also attached, but it's here on PAiATalk too:
Scott Lee
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