Re: FG502 No wave

Chris van Lint

Hi Jeff / Ozan,

Thanks for your willingness to help and advice,

Jeff: Q140 and Q175 check out OK and so do the 4 Schottky diodes.  R145 and R175 are also within limits.

Ozan: Unit set up as suggested, i.e.: Turn the dial so that output (pin 6) of U135 is about +10V, pick triangle waveform, pick 10^3 range. I cannot quite get to +10V and the dial was set to maximum which is +9.8V.

Voltage across R140 = +2.66V, across R175 = -2.52V, measured with + of DVM probe on collector of transistors.

Collector voltage of Q292 = +0.15V, R155 is quite hot and voltage at supply side is + 16.23V. No sign of any wave.

Collector voltage at Q315 = -0.6V  at Q325 = -3.5V.

Base voltage of Q230A = +0.14V (for reference base voltage at Q230B = +.05V) Both A and B were checked out of circuit and appear to be OK.

Gate voltage of Q200 = +7.9V fixed i.e.. not going up / down. Please confirm that the gate connection is what would be the base if it were a transistor.

Emitter voltage of Q210 = +0.16V This transistor gets very hot (not unexpectedly, as it is fitted with a heat sink). Q204 also gets very hot.  Cannot measure buffer function, as there is no wave.

I hope this tells those in the know what might be going on.  I have to confess, that it does not tell me much.

Thanks for all your help and perseverance


Join to automatically receive all group messages.