NO SOUND - Fatman 9308
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Author:  reedswitch [ Fri Sep 10, 2010 3:29 pm ]
Post subject:  NO SOUND - Fatman 9308

I recently completed putting together my fatman kit, but it is producing no sound.

-Power LED works
-Midi LED works
-Gate LED works

So it seems that the digital portion is working ?

Must be the analog portion, eh ?

Ive visually inspected all my soldering joints, jumpers, polarities, etc.

So does anybody have suggestions on what to check ?

I want to play this synth !!! ASAP



Author:  PAiA-Scott [ Mon Sep 13, 2010 6:20 am ]
Post subject:  Re: NO SOUND - Fatman 9308

Hello Keenan.

Maybe the negative dc supply is absent? Check the wall-mounted power source to confirm it is AC output and not the usual DC type.

The audio output connecter wires attached in each others places would prevent the normal sound. The Sleeve terminal, the same metal as the threaded metal tube should have the ground and the Tip terminal sandwiched between insulator layers and the same metal as the prong shaped contact should have the wire to the board for the audiso signal.

The ADSR control in the VCA section of the panel must be advanced clockwise (or Velocity) to get sound at the output.

More tests/checks can be found over in the bulletins/documents section for FatMan (via the Board index).

Author:  reedswitch [ Mon Sep 13, 2010 2:02 pm ]
Post subject:  Re: NO SOUND - Fatman 9308

Power supply and audio out wiring are all in order.

I started signal tracing, and I've confirmed that the VCOs are fully functioning.

The problem seems to be in the VCF section,
I cant hear the signal past R57, but i'm not sure if i'm supposed to.
I tested R57 with a multimeter and it seems OK ~98 K ohms.
No output from IC 17 , but i could hear vco2 at IC 13

Author:  PAiA-Scott [ Tue Sep 14, 2010 4:53 pm ]
Post subject:  Re: NO SOUND - Fatman 9308

Hello Keenan.

It is normal for the sound to be absent beyond the 100k resistor R57. The voltage is greatly reduced here, but you should have it at the filter output.

In the link to another topic below, you'll see the trouble-shooting pdf with voltage measurements listed for IC13 which might help confirm whether or not the LM13700 at IC17 has failed due to a possible accidental contact with the case bottom.


I see you've recently ordered the FatMan with the desktop case accessory so I'll send a replacement part and some of the stick-on bumpers.

Author:  reedswitch [ Tue Sep 21, 2010 1:20 pm ]
Post subject:  Re: NO SOUND - Fatman 9308

Thanks Scott, for sending the IC !
I replaced it , and now i have sound coming out of the main output.
But, the filter is not filtering. the cutoff knob doesn't do anything, and if i turn the resonance knob all the way down, i can only hear clicks on note-on and note-off.

Furthermore, the amp envelope has no effect.

Any thoughts?

Author:  PAiA-Scott [ Tue Sep 21, 2010 4:29 pm ]
Post subject:  Now sound, but not so Fat

That's good news. Something else must have changed. Maybe a wire broke free while the case and board were moving about during the IC replacement or maybe a voltage regulator had force against it and broke the printed-circuit below, or, caused it to be in contact with one of the others or another part.

From the 9308 FatMan trouble-shooting tips/suggestions, here are dc voltages you should find on points in the VCF and VCA sections:

For a unit that gets a Gate Trigger as indicated by the Gate LED, but has no audio output, a common trouble is an accidental short circuit causing IC17 in the VCF section to fail.. DC voltages for the pins of the IC are (count up in a ccw direction around the part from the notch): Pins 1-16, -10.84, 0.86, 0.22, 0.22, 1.4, -12.06, 1.4, 0.19, 0.13, 1.32, 7.95, 1.32, 0.23, 0.23, 0.87, -10.84.

IC18 VCA readings:

Measure to see that the V- circuit, (-)12 volt dc power supply, is getting to pin 6 and the V+, 8v dc power supply, is getting to pin 11.

Pin 1 is at about -10to11 v dc. The current flow at this pin to Q12 is about -120uA with only the VCA ADSR control, -200uA with both the ADSR and the Velocity.

Look for the V+ on one end of the 12k brown-red-orange-gold resistor R108 and about 1v on the pin 2 end. The 470ohm yellow-violet-brown-gold resistors at Rs 110 and R111 should set the voltages on pins 3 and 4 to about 150mV with about 50mV of audio on pin 3..

Pins 5 and 7 share a connection with the 33k orange-orange-orange-gold. The audio signal should develop to about 0.2-0.3V as the VCA goes 'on'. This audio should wind up at the 4700ohm yellow-violet-red-gold R112 on about a -1v dc offset before running on through the C25 capacitor to the audio Output level control, R113 and output connector J6.


The VCA ADSR voltage can be measured on lug 3 of R102, the "ADSR" control (amount to the VCA). When the Sustain Level control is at maximum, a key pressed (Gate LED On) should cause a rise in the dc voltage to about 7v according to the Attack Rate setting (almost instant when ccw and slowly when cw). The fall back to zero will be according to the Release Rate control setting. Again, fast for a ccw setting and slow for a cw setting. When the Sustain Level is less than maximum, the Decay rate comes into play and for say, a mid setting, the attack time passes, then the decay time passes and the envelope drops to about a 3.5v level for the duration of the gate. The envelope drops from there to zero at the release rate.

The VCA ADSR and Velocity controls are like a mix of the modulation to the VCA. If they are at minimum, there will be no change. To hear the ADSR action only, set Velocity at minimum and advance the ADSR control.

Sections of IC 13 are associated with the VCF and VCA so something basic to this part such as a missing supply voltage or ground might be the trouble. The sections are part of circuits which convert modulation voltages to currents which operate ICs 17 and 18, the active elements in the VCF and VCA sections. Look for +8v on pin 4, -12v on pin 11, and 0v on pins 10 and 12. A little short jumper wire with tiny solder pads located out to the side of IC18 has the important job of completing the ground circuit to many parts in the 'synthesizer' section including ICs 17 and 13. Be sure there are signs of the excess wire being clipped at each joint (no smooth, shallow dome of solder) and that there is not a break at the printed-circuit trace and solder-pad interface.

Here's to success!

Author:  reedswitch [ Sat Sep 25, 2010 1:31 pm ]
Post subject:  Re: NO SOUND - Fatman 9308

Here's what I found awry :
IC 17
pin 9:-2.71 v
pin10: -1.5 v
pin12: -1.5 v

Plus the VCA ADSR voltage at L3 of R102 peaked at less than 1 volt

Author:  PAiA-Scott [ Mon Sep 27, 2010 4:16 pm ]
Post subject:  Re: NO SOUND - Fatman 9308

Look at R65, the yel-vio-red-gold 4700ohm resistor that connects pin 9 of IC17 to the negative dc power supply. Be sure it's the specified resistor (according to these band colors) and that there is a -12v reading on the "R" end (farthest away from IC17), and, the same -2.71v you measured on pin 9.

Following are some tests and checks for the VCA ADSR sections. It might help to have the illustration supplement page from the manual for the parts placement figure 1a to help with locating parts and schematics figures 5a and 5b for following through the descriptions below. Identify and examine these points and circuits on the board too--the trouble might be found just by looking at the right spot. The diagrams showing the control wiring will be useful too.

As for the low R102-3 voltage (VCA ADSR Envelope CV or control voltage amount control), following are some voltages you should see. Note the first two on the uC output port line o13 and wiring point V are timed and to be able to notice the change you will need to set the Attack control at maximum.

Output port line o13 (originating at the IC1 uC pin 3) runs out to resistor R88 and can be measured on the "8" end of this resistor. The jumper wire near wiring point S "points" to this resistor and the 8 end is the one towards the uC. The Key-up (Gate LED off) voltage for this line is about 1.8v. The key-down voltage drops to 0v for the duration of the VCA ADSR Attack phase (about 3.4 seconds at maximum).

This voltage transition operates transistor Q10: When there is voltage to the transistor it is "on" and the voltage on its collector pin or Wiring point V is shunted to ground. When there is no voltage to the transistor it is off and the collector voltage (wiring point V) is there (from R90 and the connection of it to the V+ 8vdc circuit). Voltage on point V goes through D7 and via wire X to the Attack control R94 and the setting of this control varies the resistance and the time it takes the voltage to charge capacitor C19. Op-amp stage IC12:D copies this weak energy that is the charge on 19 to a stronger voltage that is the ADSR Envelope CV. So, as C19 charges, the output of IC12 follows suit.

Here's where things can go wrong as the ADSR Attack is dependent upon transistor Q10 switching and transistor Q10 switching is dependent upon the Attack phase (setting the duration of the o13 pulse). IC8:D is a comparator stage and it's job is to indicate which of its inputs is most positive. When pin11 is most positive (normally 7v Vref voltage as set by resistors R85 and R86 and shown schematically up by the VCF AR circuit), the output is 5v--when pin 10 is most positive, the output is 0v. This voltage level is a signal back to the uC as to the state of the ADSR. When it drops from 5v to 0v, the uC input port line i1 changes state from 0v to 5v with the IC7:E inverter stage on IC8's output pin 13. This i1 port line signal to the uC pin 12 starts the ADSR Decay phase and the o13 port line goes back 'high' or to 1.8v, turning 'on' transistor Q10.

Q10 zeros the voltage at point V and the setting of the Sustain control adjusts the amount of voltage the Decay control and wire W 'sees' via D6. When the control is anywhere less than maximum the charge on C19 has a path for discharge and the ADSR Envelope CV decays to this Sustain level (or just stays at a maximum 7v) for the duration of the key-press.

When all keys are up and the Gate LED is off, uC output port line o14 goes 'high' or to 3.7v from the 0v key-down level. This turns 'on' transistor Q11 which then provides a discharge path for any 'sustain' level charge remaining on C19 via the release control and wire Y through R95 and D8. The setting of the Release control R96 affects the resistance C19 'sees' as it discharges towards zero through the 'on' or conducting Q11.

If nothing turns up, it might help to send me a photo of the top and bottom sides of the board. I might be able to spot something. Or let me know if you'd like me to send the service form/information with instructions and details about getting it in here to be put in working order.

Author:  reedswitch [ Sun May 01, 2011 7:43 pm ]
Post subject:  Re: NO SOUND - Fatman 9308

Just got back to working on it, after far too long of a hiatus.

R65 = -12v on the "R" end, and -0.12 on Pin 9

I'm thinking I'd probably just like to send it in and get it working if i cant figure it out soon.

Approximately how much would that cost?

Author:  PAiA-Scott [ Mon May 02, 2011 10:39 am ]
Post subject:  Re: NO SOUND - Fatman 9308

Email me,, and I'll reply with the service authorization form/information.

Here are details about service:

It averages about $30-50 with the shipping added.


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