Ken stone quad universal slope generator debugging

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lilnoah95
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Ken stone quad universal slope generator debugging

Post by lilnoah95 » Tue Sep 15, 2020 2:52 pm

Hi all, I'm posting in the hopes that someone familiar with the DUSG can give me some pointers on how to troubleshoot this module. Only 1/4 slope generators is buggy, but that one has a whole bunch of problems. Here is a list of the issues with that particular quadrant and a video to help visualize:
  • "Rise" knob does nothing, and the "Fall" knob controls the speed of both rise and fall.
  • The positive output is inverted and the bipolar output is not sending anything.
  • When the "VC In" switch is set to Rise or Fall the frequency of both the rise and fall portions becomes extremely fast - (not stuck on high as i said in the video).
  • This function generator bleeds into the other function generator attached to this Dusg board.
Any ideas on how to troubleshoot would be highly appreciated. Thanks.

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artilect99
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Re: Ken stone quad universal slope generator debugging

Post by artilect99 » Wed Sep 16, 2020 3:33 am

If these are the CGS114 boards all I can say is good luck. I built one of these a few years ago -- one half worked perfectly, one half still does not work to this day. These specific boards are notorious for being problem-prone... the one I got was bowed in the middle, and I suspect there is a broken trace somewhere in the non-working half that I don't have the patience to track down. The tracks tend to peel up from the board and cause intermittent weirdness among other things. Tim Stinchcombe did a very thorough analysis of this circuit and while ingenious, the fact that it is so complicated makes it hard to debug (IMO at least).

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cygmu
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Re: Ken stone quad universal slope generator debugging

Post by cygmu » Wed Sep 16, 2020 5:16 am

Since the LED is working ok, this tells me that the main output must be correct on the board, so I suspect something has gone wrong in the wiring of the DCO and Bipolar Outs to the panel. The bipolar output is inverted (and offset) from the main output so it could be that you have accidentally wired the bipolar out to the main output jack, and got some kind of short to the bipolar output jack which kills the output.

The rise/fall/both switch behaviour is strange but could result from a wiring error or short too: check that the centre lug of the switch is connected to ground and not e.g. to -12V. (Do you have a meter to verify this?)

It's quite a large circuit and the whole thing is a big loop so everything affects everything else which does make troubleshooting tricky without taking tons of measurements, but a good look at the panel wiring would be my first step.

lilnoah95
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Re: Ken stone quad universal slope generator debugging

Post by lilnoah95 » Thu Sep 17, 2020 4:58 pm

cygmu, i can't thank you enough! i have fixed the issues with the DCO and bipolar outs, which was more or less exactly what you diagnosed. I also have gotten the rise and fall knobs to work independently, which also had to do with wiring.

I am now seeing another issue:

when i patch the slew generator to self-oscillate, the rise/fall/both switch seems to have an effect, even when nothing is plugged in. specifically, when i set it to "rise" the oscillating wave rises in frequency. i'm going to double check all the wiring and see if it's another simple mistake. also, there is still bleed from one oscillator to the other.

update: i fixed all of the wiring of the VC in jack and the switch, but the problem still remains. Any ideas what could be causing the above problems?

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