Fatman problems?

Alex Noble alex at elbon.demon.co.uk
Tue Dec 2 00:02:55 CET 1997

I've fianlly got all the bits and pieces for my fatman, (thanks to chris
crosskey - cheers), and the assembly seems to have gone as planned, no
real problems there, and I can't see any faults in the solderwork.
But... it doesn't work. The midi light flashes when the input is
activated, but the gate light and voltage doesn't respond, and there's
no sound.

The pitch and velocity cv out are about -1v, and under normal
circumstances, the gate cv is 0v, but sometimes when the unit is turned
on, the gate led is automatically lit, and the cv is +5v. This lighting
is intermittant, though I can't find any physical faults in the

Also, if I turn the output up to maximum, I can hear a buzz which I
assumed was the mains hum, though it may be the actual vcos. Turning up
the vca velocity and adsr controls makes this louder, the "pitch" knob
makes the pitch of the buzz lower the higher it is set, and vice-versa,
and the offset knob produces neat phasing effects, like well, er,
offset. None of the other controls make any difference to the sound.

I'm running it off a wall-mount 12v 1A transformer, which I thought
might have something to do with it, since the manual specifies 12-24v... 

I thought I might have fried some of the digital ICs during
construction, but I've replaced the 74HC373s and the 74HC14 too, which
the same result, Is there any way to test if the microprocessor is the
part at fault? Does anybody have a record of what voltages might
typically be found at various points on the board so I can try and trace
the fault? Everything sounds and works the same whether the digital ICs
are installed or not.

There is a correct voltage at pin 8 on the 6n139 and pin 14 of the
74hc14 too.

Any ideas or suggestions will be very greatly appreciated, many thanks,
see jah!

Alex Noble.........................................alex at elbon.demon.co.uk
  Wicked original music for your ears: http://www.elbon.demon.co.uk/es/
                     Home of Euphy Scott Productions.

More information about the Synth-diy mailing list