9700s troubleshooting
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Author:  gzifcak [ Mon Jan 10, 2011 2:55 pm ]
Post subject:  9700s troubleshooting

I've sent an email to Scott, but while I'm waiting for a response I thought maybe someone else might have some ideas:

I've assembled the 9700s, and every function seems to work so far (yay!) but I'm having a problem that seems power supply related. I'm using a 12VAC 1300mA transformer.

The symptoms are lots of hum and strange cyclic behavior, and a growl in the VCOs and VCF that sound like they're around 60 hz.

I've verified that the SG and G circuits of the 9720, 9730 and 9710 are separate without the 9700 connected.

I created my own single faceplate and connected all the panel control grounds together, then disregarded the panel-to-board ground connections for all but the 9700 board. I assumed a single ground path from board to panel controls would be better. Should I instead separate the grounds for each module's panel controls and run them separately to the boards?

With no other module connected to the 9700 MIDI-to-CV converter, I get a reading of +15 and -17 volts on the power connector. When i connect the 9720 VCO, those dip down around 12 and 14. When I measure the voltage regulators, I get around 12 volts out, but that dips below 12 when the modulator cycles.

Is my supply not providing enough current? Could there be an error in my 9700 construction that would cause the asymmetry? I'm hoping to get a hold of a bipolar regulated supply to test it with that soon.

One thing I don't understand: I read that the transformer leads should not come into contact with the panel (hence no power jack), but one connects directly to the 9700 ground (via G), then back to the panel control ground's bare wires (via SG) which can easily touch the panel. what's the difference?

Thanks a lot,

Author:  gzifcak [ Tue Jan 11, 2011 8:05 pm ]
Post subject:  Re: 9700s troubleshooting

I found the problem. Somehow I had 470 uF caps in place of the 2200 uF caps in the power supply. It's running nice and clean now.

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