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No sound out new Fatman build
http://www.paia.com/talk/viewtopic.php?f=8&t=495
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Author:  Robzim [ Sun Mar 03, 2013 12:28 am ]
Post subject:  No sound out new Fatman build

Hi everybody,

I am the proud owner of a freshly built Fatman with no sound. Power, midi and gate leds are working. But no sound at the outout.

First time I turned it on I had sound, but had difficulty getting it into tune. When the tune button was centered, the tone would be a very low frequency (I could count the clicks). When turned right it would go many octaves up. Same when turned to the left, but to a lesser extent. Tuning it correctly was nearly impossible as it was it was difficult/impossible to get a stable pure note out (I checked with an electronic tuning device I use for my guitar). So I decided something was wrong and went back to fix the components and solder joints.

I found a few badly soldered joints and fixed them. In the process, I noticed that where C22 and C19 meet, the round bit of copper on the PCB had let loose. I added an extra blob of solder to make sure everything connected. I connected the Fatman again, but now there was a new problem: no sound. I double checked all joints again. I used lead free solder and I read this may lead to problems. So I reheated all joints around the ICs again to make sure everything was well connected. I seems fine when looking at it, but still no sound.

I did some signal tracing and found out the VCO 1 and VCO 2 are working. Sligthly different tones with clicks at different frequencies. There is sound at pin 9 of IC 17, but with irregular clicks.

I consulted the troubleshooting guide and tested the voltages:
Power adapter reads 11,5v AC = NOT OK, should be 12v (not sure if the difference is enough to be a problem?)
Pin 40 of IC1 reads +5,04v = OK
Pin 4 of IC10 reads +6.66v (I kid you not) = NOT OK, should be +8v
Pin 11 of IC10 reads -9,45v = NOT OK, should be -12v
Pin 4 of IC13 reads +6.70v = NOT OK, should be +8v
Pin 11 of IC13 reads -9.46v = NOT OK, should be -12v

So there is a problem with the voltages. I checked the voltage regulators. The right components are in the right place. One solder joint on IC19 looked dodgy, so I resoldered that. No Solution. So I resoldered (with lead solder) all the voltage regulators joints. No difference. I resoldered all joints leading to one of the 9 voltage regulator pins. No difference.

I measured the voltages of IC17:
1: -8.2v = should be -10.84
2: +0.82 = should be +0.86
3: +0.19 = should be +0.22
4: +0.19 = should be +0.22
5: +1.41 = OK should be +1.4
6: -9.6 = should be -12.6
7: +1.41 = OK should be +1.4
8: +0.19 = OK, should be +0.19
9: +0.07, should be +1.13
10: +1.2, should be +1.32
11: +6.59, should be +7.95
12: +1.19, should be +1.32
13: +0.19, should be +0.23
14: +0.19, should be +0.23
15: +0.82, should be +0.87
16: -8.39, should be -10,84
Lots of voltage problems there.

IC18
Pin 6: -9.77, should be -12v
Pin 11: + 6.68, should be +8v
Problems consistent with IC10 and IC13

I measured the voltages at the feet of the voltage regulators. There, the voltages are not correct, same as the wrong voltages at e.g. the IC18 pins.

So the voltage regulators seem to be a problem. What can be done about it? And I assume there is also another problem causing the lack of sound at the final output. Any ideas?

I suspect the lead free solder may cause many problems. Does it make sense to remove all lead free solder with a desoldering pump and to resolder everything with lead solder?

Hope you can help.
Many thanks in advance,
Robert

Author:  PAiA-Scott [ Mon Mar 04, 2013 1:06 pm ]
Post subject:  Re: No sound out new Fatman build

Hello Robert.

The no-lead solder wouldn't keep things from working, it is just more difficult to make good joints and the extra heat it needs makes it more likely the adhesive for the printed circuit can give way and detach from the board. This can result in a break, opening the circuit, particularly when the joint is for a taller part like a capacitor or a wire which can work like a lever against the joint.

If not enough heat is used as the joint is made, the solder might not flow to to all the metal surfaces in the joint -- either the pad or the wire or component lead.

It seems like there might be a bridge of solder that's putting a load on the power supply resulting on the voltages being low.

Double-check to be sure all the ICs are installed in the proper directions with respect to the board graphics.

None of them should be very warm or hot to the touch (normal for the voltage regulators though).

About the low pitches you heard at first for non-extreme pitch settings, I wonder if you might have used the rack-panel control mounting diagram and did not see the 'exploded' 10k pot for the Pitch control R34. This is an easy mistake to make and it can lead to a 1M being installed at the Pitch control, and the next two pots being wrong too--then it works itself out.

The value of the potentiometers is marked on the brown layer facing the panel, but there are codes marked on the back and the one at the Pitch control should have the same markings as the other 10K panel pots.

Your mention of the lifted printed circuit at Cs 19 & 22 might explain the loss of sound. C19 is in the VCA ADSR circuit section and without the ADSR voltage to the VCA, the Velocity is the only control to open the VCA and let the sound through.

Inspect this area again. The node including the end of C19 not joined with C22, and wiring point Z, breaking, would result in no VCA ADSR, or, the joint for Z is very near a joint for a jumper wire for the ground -- double check to be sure there is not a bridge here.

Image

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