my FF just died!

[mcv]

i tried installing a 10K bias trimpot to my dunlop FF reisue; i desoldered the 8.2k resistor and soldered the trimpot and when i pluged in i get no sound! nothing at all, only when bypassed.
did i do something wrong?

[Samuel]

Three possibilities (I'm assuming you've played around with the trimpot to make sure its just not misadjusted)...
1) cold solder joint, remelt the the solders for the trimpot
2) overheated the transistor either when desoldering the original resistor or soldering in the trimpot
3) positive you're using the correct two legs of the trimmer (assuming its got three, some only have two, right?)

[mcv]

well, i removed the trimpot and soldered the 8.2k resistor again and it still does not work.
how do i check if i overheated the trannie? i´m pretty sure i didn´t because it was just so fast and easy to remove the resistor.

[niftydog]

how do i check if i overheated the trannie?

It may not have been the heat.  I guess it is possible that the trimpot presented a short circuit from collector to negative.  That, combined with the fact the tranny was still biased, may have toasted the tranny.

There is a way to check it if you have a multimeter.
You'll need to first identify the transistor, work out if it's PNP or NPN (there's two versions of the circuit) and then work out which pins are the base, collector and emitter.  Use your multimeter diode check (or even a high resistance range) to read the PN junction.

For a PNP tranny, there should be a diode "action" from emitter to base.

For a NPN tranny, it's the same, but from base to emitter.

Or, a relatively low resistance from P to N (ie; emitter to base for PNP or vice versa for NPN) and a relatively high resistance in the opposite direction.

Sometimes you will get similar readings from collector to base (or emitter to base) but the lower resistance of the two is the base emitter junction.

If you read a short circuit anywhere, the tranny is toast.  If you can't find a diode by any means, it's probably also toast.

Have I confused you yet?!

I guess another way would be to do some DC voltage checks around the circuit.  Maybe do this; plug it all in like you're about to use it.  Clip one lead of you multimeter to the negative battery terminal.  Measure the voltages at each pin of both transistors and get back to the forum with your results.

[mcv]

hey, i´m a newbee here!
i will check all voltage reads and post here, maybe i will understand you better after that, thanks!