Re: FG502 No wave


Chris van Lint
 

Many thanks to all who have provided input.

Prof. Lee's explanation was most useful, however full disclosure it was still a tad above my paygrade and after about 4 reads, I think I got it.  Andy's suggestion to have a look at Alan's video was most useful and it helped me understand how diodes are used as a switch. Finally I followed Jeff's suggestion and checked the gate at Q200 and confirmed there was no wave form there.  Back to basics and I checked for current movement from U200, to Q200.  I have included an image of my readings, but I am not sure whether the list allows embedded images, so here is a description: /(in the meantime my first message was rejected due to the image)/

U200 Starting point around "1" on the frequency adjustment dial = +0.1V. turning the control CCW increases the voltage gradually to +9.7V. It then jumps suddenly to +17.85V and as I turn another 2-3 sub-divisions, it jumps back to +0.1V, the starting point.

U135 Starting point around "1" on the frequency adjustment dial= +7.28V. turning the control CW increases the voltage gradually to +19.7V

U140 Starting point around "1" on the frequency adjustment dial= +6.67V. turning the control CW increases the voltage gradually to+16.43V when it jumps suddenly           to +19.1V, stays there a few sub-d-visions and jumps back to +6.67V, the starting point.

Q200 gate NO triangle waveform

U170 Starting point around "1" on the frequency adjustment dial= +7.2V. turning the control CW increases the voltage gradually to +18.00V.

U175 Starting point around "1" on the frequency adjustment dial= -6.49V. turning the control CW increases the voltage gradually to -18.15V.

I am stumped.  The Opamp current sources appear to be OK and I would appreciate some advice on the next things to check.

Chris

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