First pedal no output

Forum dedicated to helping people debug and troubleshoot non-functional pedals or builds. Please use an clear and informative title, indicating circuit and basic problem. Don't forget to mark the issue as fixed if this is the case.
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Valerio313
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Post by Valerio313 »

idy wrote: 30 Apr 2021, 05:21 When they say "check solder joints" they don't mean just look, but go over them again with the iron, reheat to make sure everything is connected. (not too long near the transistor, but your is socketed, sockets are often not good connections. Make sure it is firmly in place.) Often I've had things that look fine but a "cold solder" joint makes a bad connection.
That's exactly what I did, I've basically redone the whole soldering. When I check for voltages during the error, I "touch" the transistor itself, so I guess it's making contact with the socket. In any case, the error occurs in an almost timed way, I don't think joints stop connecting exactly after the same amount of time.
idy wrote: 30 Apr 2021, 05:21 You can't measure the value of a resistor when the power is on! And it is difficult to measure it "in circuit," but you can get some results, you have to look out for parallel R's or even a transistor that may act as a diode.
I'm not trying to measure resistance with the power on; I measure it right before powering up and straight after. R2 values does change, and you can see the value changing on the multi-meter going slowly back from 18k to 100k (already replaced that resistance and cheeked with a new one). As soon as R2 reaches back 100K, you can power on and the system starts working again (for few minutes).
idy wrote: 30 Apr 2021, 05:21 I would also, power off, measure for continuity between all the places that should be connected by the traces on the PCB. Sometimes a trace gets lifted or otherwise spoiled on a PCB, and although things look good, a connection is "open."
I checked the board continuity plenty of times by now, both before and after powering up. I usually test it touching resistors themselves rather than the solder joint on the back of the PCB
idy wrote: 30 Apr 2021, 05:21 Not sure why you took out C2.
I was trying to reduce the circuit to the smallest number of components, but still having it working (in this case, I used schematics of normal boosters, and I removed what I saw it was not present on those. It still didn't make any change...

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Valerio313
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Post by Valerio313 »

Manfred wrote: 30 Apr 2021, 15:48 I had an idea and ran a simulaltion in which I changed the 2N5088 model.
I gave the transistor a larger base-collector reverse current of about 50 Mircoampere and I reached the approximate voltage values measured in the fault case.
The behavior in this order of magnitude is known only from the germanium transistors, there this reverse current increases with the heating in the time.
In this case the transistor must be faulty, how crazy that would be. :scratch:
Try some other transistor type and pay attention to the pin assignment.
I really appreciate your help, but I think this is getting way too technical for me... I'm studying how amplification circuits work for fun and to understand how my pedal works, but I don't have any knowledge in electronic.

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Manfred
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Post by Manfred »

This is my last idea, since everything else has been checked and found to be OK.
Remove the socket and solder the transistor directly, maybe there is a problem with the connection.

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phatt
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Post by phatt »

Q have you verified the pin out of the Transistor?
A decent DMM's will likely have a transistor test function.
Phil.

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Valerio313
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Post by Valerio313 »

Manfred wrote: 01 May 2021, 15:03 This is my last idea, since everything else has been checked and found to be OK.
Remove the socket and solder the transistor directly, maybe there is a problem with the connection.
It seems like the socket works; I checked the transistor's voltages directly on the pins of the transistor itself and on those resistor connected to the transistor, and I have the same results. Which means there's continuity between the transistor and the rest of the PCB.

I realized now, after have removed everything and solder everything back in, that R2 value is now fixed at 70K once onto the PCB it goes back to 100K if I remove it. According to my understanding, R2 is not in parallel to anything and it should read 100K even when in the circuit, is that correct?

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Valerio313
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Post by Valerio313 »

phatt wrote: 01 May 2021, 22:07 Q have you verified the pin out of the Transistor?
A decent DMM's will likely have a transistor test function.
Phil.
I don't have a professional DMM... The only way i have to test the transistor is using the Diod function. Both transistors I have read 626 between base/emitter and 619 between base/collector.

Moreover, in those few minutes when the pedal is working, voltages on the transistor are correct, according to the values Manfred gave me

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Post by phatt »

OK,, then maybe the 2n5088 BJT's you have are faulty.
I'd be trying another transistor ,, heck any small signal NPN device that is CBE or BCE will work in such a simple circuit and at least tell you if the circuit is in fact working as it should.
You may even find other types work better.
Phil.

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