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 Fatman Troubleshooting 
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Joined: Wed Feb 22, 2012 12:51 pm
Posts: 5
Post Fatman Troubleshooting
I just finished my Fatman build and it sounds awesome! I am having trouble fixing a few issues.

1. Offset is affecting Oscillator 2 at the extreme CW end, I think this is supposed to happen?

2. Glide is working, but at the extreme CW end it only takes about 1/2 a second instead of a few seconds to glide.

3. The VCF envelope controls are not working at all. The A(S)R knobs responds as it should, but the AR/ASR switch, Attack, and Release controls do not do anything. The VCA envelope is working just fine.

4. The Punch switch is not working, it does not affect the sound at all.

I have checked all the solder connections, component polarity, etc. and everything looks fine to me. I am, however, very inexperienced with electronics. Are there any tests I can do to determine the problem?

Everything else on the synth is working great and I am very happy with it. Looking forward to working out the bugs and getting it finished!


Wed Feb 22, 2012 4:19 pm
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Joined: Sun Nov 09, 2008 2:49 pm
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Post Re: Fatman Troubleshooting
I just finished my Fatman build and it sounds awesome! I am having trouble fixing a few issues.

Great! Sorry for this delayed response, I've been playing catch-up.

1. Offset is affecting Oscillator 2 at the extreme CW end, I think this is supposed to happen?

Well, it really shouldn't happen, but then there's a knob for that. A big change in the VCO #1 Offset causes a change in the load on the main Pitch control and this can be detected as a slight change in pitch in VCO #2. Just to go back and tweak the main Pitch control should bring things back in line. The VCO Anti-phase-lock modification (for longer, slower beats between closely tuned VCOs) over in the Technical-Bulletins/Assembly-Notes (FatMan Modifications) section of PAiA Talk has the added benefit of greatly reducing this (and Pitch change with adjustment of Glide) with the substitution of op-amps having greater input-impedance, lightening the load circuits preceding them (Pitch and Glide potentiometers).

FatMan VCO APL: viewtopic.php?f=15&t=238

2. Glide is working, but at the extreme CW end it only takes about 1/2 a second instead of a few seconds to glide.

Glide occurs as the pitch cv change is delayed by the resistance of R32 a 1M potentiometer providing a charging path for 0.1uF (104) capacitor C12. Check R32 to see that its marking is the same as other 1M pots in the kit Rs 82, 84, 86, 92, 94, and 96. There is a mfgrs. code stamped on back, but the value is marked on the side facing the panel. Most likely, all the 1Ms in the kit will have the same mfgr. code. Check C12 to be sure it is marked 104 and that its solder joints flowed to the wire and printed-circuit pad on each leg. The printed-circuit trace for ground for C12 passes through the + marked leg of capacitor C6 and this is an electrolytic that stands up taller than other parts in this middle area of the board: Maybe force against this part when folding the board inwards during final assembly caused a break in this ground circuit over to C12.

This topic describes repairing broken/lifted printed-circuit pads/traces: viewtopic.php?f=7&t=344

3. The VCF envelope controls are not working at all. The A(S)R knobs responds as it should, but the AR/ASR switch, Attack, and Release controls do not do anything. The VCA envelope is working just fine.

A likely possibility here is a solder that didn't flow on the panel connections for these controls. There's a link joining their lug-1 and a wire from there to R on the pcb. If this isn't it, check the solders for transistor Q7. As the gate-trigger activates/deactivates electronic switching of voltage levels on its collector leg (this 2N4124 has the pin-out Emitter-Base-Collector reading left to right viewing the flat face). When a key is pressed the leg should have eight volts, when released, zero volts.

4. The Punch switch is not working, it does not affect the sound at all.

It might be OK -- it's only noticeable with a percussive VCA envelope/transient. To notice Punch, set the VCA ADSR controls for Fast Attack and Decay times to a low Sustain. When On, the pip of this fast transient should be more pronounced than when the switch is set Off. If no difference, check the soldering to the switch and it's wire connections to the pcb points U and DG.

Here's to success!

_________________
Scott Lee
scott@paia.com


Fri Feb 24, 2012 12:46 pm
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Joined: Wed Feb 22, 2012 12:51 pm
Posts: 5
Post Re: Fatman Troubleshooting
Thanks so much for the help, everything is up and running! The problem was bad solder joints on a few of the panel pots and a bad connection from Q7 and one of the resistors in the filter envelope circuit. It sounds amazing.


Mon Feb 27, 2012 8:06 pm
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