FG502 No wave

Chris van Lint


I have been following the thread related to the FG502 with no working FREQUENCY control with great interest and I was both impressed and encouraged by the large number of responses from members who are obviously quite familiar with this unit.

I have a FG502, which initially had a power supply problem.  I fixed this by replacing one of the 741 and it was running great, until recently when all of a sudden there was no output at all.

I have checked the+20V, -20V, +17V and -17V supplies and they are all spot on.  I understand from the "theory of operation" that all output waveforms are derived from the triangle generator.  I have to confess that understanding exactly how this waveform is generated with those CRs is a tad beyond my paygrade and I would be grateful for some advice from those who understand this stuff.

Where is the earliest point in the triangle generator, I should be able to see this signal on my scope.

Perhaps a stupid question, the circuit diagram shows a square wave at R255.  Is that wave there even if the triangle is not being generated.

Any other advice on where to start looking would be greatly appreciated.


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