? blown transistor in Fuzz Face

[m7b52000]

I have built a NPN FF/ Tonebender Mk1.5 on a vintage style circuit board (see pic) It has been working perfectly but today it is silent. All solder joints have been reflowed and there are no bridges or stray wire strands shorting anywhere that I can see. Audio probe demonstrates a weak (less than unity) signal at Q1 C and nothing at Q2 C. Voltages at Q1C, Q2C, Q2B and Q2E are all roughly 1.7 V. Previously these voltages were all pretty standard i.e Q2C 4.4 V. Is this consistent with a blown Q2?

Thanks

[Clint Eastwood]

The voltage at the base of Q2 should always be 0.6 volts higher than at the emitter, assuming you are using silicon transistors. So the measured voltages seem to indicate a faulty Q2. Why not take it out and check with a multimeter? do you have one with a transistor tester?

[m7b52000]

That was my next step but I wasn't sure if my thinking was correct!

[antonis]

Could you plz measure voltage at Q1 Base..??

And post a schematic of your circuit, with items particular values..

[m7b52000]

Q1 B is 0.8 mV. Schematic attached. It was working perfectly before - this is why I suspect a trannie has gone bad.

[GibsonGM]

If you have to unsolder it and might want to keep it, try to get a heat sink of some sort on the legs of the transistor - they don't like heat...just sayin'. 

[antonis]

Before unsoldering BJTs, check R5 (100k feedback resistor) for proper connection to Q1 Base and Q2 Emitter/Fuzz pot..

[m7b52000]

Before unsoldering BJTs, check R5 (100k feedback resistor) for proper connection to Q1 Base and Q2 Emitter/Fuzz pot..

I have now checked every single connection and there is continuity everywhere there should be. There are no unwanted grounds. I think removing Q2 is the only option left?

[Clint Eastwood]

Since they are germanium transistors, as GibsonGM says they don't like heat. I suggest you use sockets for them next time. They can get damaged from the heat, maybe this caused the failure of one (or both?) of your transistors.

[pinkjimiphoton]

Before unsoldering BJTs, check R5 (100k feedback resistor) for proper connection to Q1 Base and Q2 Emitter/Fuzz pot..

I have now checked every single connection and there is continuity everywhere there should be. There are no unwanted grounds. I think removing Q2 is the only option left?

if it was working before, its unlikely the transistor got smoked being soldered. try holding the tip of your iron near the case of the transistor that's suspect, with everything plugged in and powered and see if it suddenly swells back in at some point. they can take a good bit of heat... if it comes back up as it heats up,  you have a classic case of northern hemisphere disease.

ge stuff doesn't like to be too hot, but if it gets too COLD it won't do ANYTHING but look at ya funny sometimes.

if it comes back up, cool.

check this link out... sometimes, you can reverse bias a leaky ass ge diode in parallel with b/c and compensate for temp sensitivity.
sometimes.

it IS also possible ya popped the q. especially if modern production crap from the peep's republic..


but.... did ya check your volume pot? sometimes, if there's a shorted output cap, it can literally smoke the track inside the volume pot. these suckers tend to get kinda loud...