Here are some specific insights into the synthesizer board.
First check that you have the output in the correct jack. Remember we called one TRS and one NC-TS. The TRS is the output. There does not have to be anythign connected to the NC-TS for the unit to operate.
Here are some DC measurements you should find on the ICS.
The pic is the MIDDLE IC.
Pin 1 of the MCU (PIC12F683) Should have 5 volts. If you are measuring something higher disconnect power immediately. Verify that R18 is installed correctly and that the Zener Diode D2 is oriented in the correct position. One side of R18 should show 9 volts and the other 5 volts.
Pin 8 of the MCU is ground. All other pins may vary during operation.
This is the op amp labeled TLC272 on your handout. Im not sure why it dosnt say 2272. Pin 8 should show 9 volts. Pin 4, 5, 6 and 7 should show 0 volts. Pin 3 should show around 2.1 volts.
This one is labeled TL072 on the layout.... Pin 8 is 9 volts. Pin 4 should show 0 volts. Pin 3 and 5 should show around 4.5 volts.
3) General Signal Flow
If you have an oscilloscope you can try to follow the signal incase it is being generated but not making it through the volume modulation.
Power on the instrument and hit the red button once to advance it into the sound generating subroutine. measure the output of pin 5 6 or 7. you should see square waves with 5v peak to peak. If you dont see any output on any of these pins keep depressing the red button and measuring. If no signal is obtained there is a flaw with the mcu itself.
If you see some squares there move on to pin 7 of the RC4580. The output of this should show (with some DC offset) a signal of somethign in the order of 2 volts peak to peak. If you see nothing on your screen make sure you have compensated for the dc offset either by adjusting the vertical position or switching to AC coupling.
Still nothing? there is problem with this op amp. Double check the power on the pins mentioned above.
If you have something on pin 7 check on the tip of the NC TS, you should see the same thing there. And accordingly on the switch side of the NC TS.
Now check the output of the 4580 on pin 1. If you have something here but no output on the jack then double check that you have "out" on the pcb wired to the TIP of the TRS.
4) Probe Response
my probes do nothing
Disconnect the probe assembly from the unit. Set your multimeter to a 200k or 2M ohm range. You may have to remove the hood from the connector to verify you are measuring the correct pins, but in general you should read a resistance that varies from about 500 ohms to over 100k across the red and black wire pairs. ie the resistance across each probe should vary when it is exposed to light. If the resistance is infinite or you measure open circuit and see no variation then either there is a disconnect at the photocell or a broken connection at the plug. Make sure the black and red wires are securely soldered onto the plug pins by gently tugging them. If you measure a very low resistance that dosnt vary then the red and black wires are shorting somewhere.
the change in response caused by the pots is radical, abrupt and does not vary over the whole rotation of the pot
De solder the wire on the two outer pins of the pot and exchange them. ie the wire that was going to the left side now goes to right and vice versa.
I will add more later. Please post in reply or email me if you have specific questions.