Giant CGS Analog Computer Troubleshoot

[Phillip Jeffries]

Hello all. I'm right in the middle of a trouble shoot of the collection of cgs pcbs in the bridechamber Analog Computer module.

Here are some photos:

http://www.flickr.com/photos/27931879@N08/sets/72157610880297572/

Here is a comprehensive description of whats wrong

The left inverter works fine, but there is no signal out on the right inverter with anything plugged into the inputs, or not.

Both gate converters just output a negative voltage (is that correct? It makes a vco drop in pitch when it is applied, so I'm guessing its negative). Neither gate converter responds to any kind of signal, slow or fast, I just get the constant voltage out.

The and / or sections dont do anything. There is a very small positive voltage coming out the output.

On the pulse divider, all outs / reset / reset switch work as they should, except the 3 and 6 which output a constant positive voltage.

And the ASR works, but I have a question. When nothing is plugged into the input, but with it clocked, and with one output plugged into a vco, the vco steps slightly in pitch with the clock. Should it be doing this, even with no input voltage present for the asr to respond to? Also, the steps are slightly different pitches depending on which output of the asr is chosen.

Bear in mind I'm totally new at this, prior to this have built exactly 2 guitar pedals and two filters (but they all work fine). I have access to a digital multimeter, but not a scope (except a software one which seems to work actually but I'm sure its not good for exact measurements).

Thanks for any help!

Oh I should add, the xor xnor works fine.

[andrewF]

debugging is fun!


re:and/or
check the LEDs are not reversed, transistors correctly installed?

re:pulse divider
outputs 3 and 6 both come from the same 4017 IC, and are the only outputs driven by this chip. Trace the circuit back to see which chip it is on the PCB. Check all the pins on the chip are powered correctly/grounded/properly soldered as per the schematic. Replace the chip after exhausting all other possibilities!

re:ASR, I'm no expert but maybe -
with nothing on the input, as the clock ticks over the caps in the S&H circuits are recharged and then droop slightly until the next cycle. This is the slight change in pitch you are hearing. Each output is being fed a different S&H signal, so will sound different.