@billy
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There’s a gutshot on the old forum from Trom not that it reveals much
https://guitarpcb.webs.com/apps/photos/album?albumid=15907201&pagesize=60&page=3
Everything looks the correct value and orientation can’t see the colour bands on R3 and values of C4 and 5 or clearly trace your wiring to the in jack
From your description that you can hear it faintly sounds like you’ve got a bad connection/ poor solder joint
This is a small circuit so maybe a good opportunity to make and use an audio probe whereby you’ll probably find your problem very quickly and learn a valuable debugging skill
https://drive.google.com/file/d/1T9OsJ0riQhm1QFWPfNQ5q5guikuFKDRN/view?usp=drivesdk
When you say audio signal tracker do you mean an audio probe to check for audio signal
I’m not sure what you mean by audio signal tracker
Great! you have an audio probe check if you get audio at pin 14, IC2.
With D3 it’s what voltage you get going in and coming out it does appear to be working correctly with what you have coming out of pin 14 IC2 and going into Q2 base dropping around 0.3v as expected
I think your problem may be around pin 14
It’s very difficult to see and trace your wiring Richard do the white wires go from the main pcb white square in and out pads to the BI and BO pads on your 3PDT pcb
It may seem a bit of a daft question but do you have your guitar cable going to the IN jack and your amp cable going to the OUT jack
It’s easy enough to mix up your IN and OUT with the pcb the wrong way up and your IN on the left instead of the right
Not that it matters but I notice you have your stereo jack on the OUT side, but may have thrown you it normally being on the IN side
If you plugged your cables into the wrong jacks you would still get bypassed signal but no effect
A very common mistake beleive me I still do it!
Post some images where we can see and trace the wiring to your DC jack, in and out jacks and 3PDT switch Richard
You wouldn’t be able to accurately measure resistances in circuit
Your Q1 and 2 voltages look off compared to the voltages listed below
I think you have IC3 in and out mixed up the out would be the pin with 5.5v
What are your voltages both sides of D3
IC2 all pins would be around half power except pins 4 power and 11 ground your pin 14 is a bit high so it’s just a case of finding out if this is where your problem begins it could be anything from a simple dry solder joint to a faulty component a few of your solder joints look dull and a few ball like which can be dry inside
You could reflow all those joints holding your iron on each for around 3 seconds until you get a nice flow and a good connection between component and solder pad
Be careful you don’t apply too much heat set your iron to around 400° Celsius and remove your ICs and transistors from their sockets
Unfortunately I’m at work on my phone and can’t zoom in to check everything but all your component values and orientation look correct
Working unit voltages
LM13700
1– 1.34 16– 1.34
2– 0.69 15– 0.69
3– 3.56 14– 3.56
4– 3.58 13– 3.57
5– 4.75 12– 4.78
6– 0.00 11– 7.22
7– 4.75 10– 4.78
8– 3.56 9– 3.57
Q1: (7.27 – 3.71 – 3.23 – DSG) Drain Source Gate
Q2: (5.05 – 3.75 – 2.90 – CBE)
Q3: (5.05 – 2.90 – 2.86 – CBE)
Check the solder joints on your transistor sockets if they’re good you can place the transistors in the sockets a little wiggle sometimes helps to secure them what you can then do once they’re in nice and tight is solder 1 of the transistor pins into the socket to keep them in place
If you have spare sockets try fitting a transistor into them till you feel them locking in this will also space the pins out, as I say I find wiggling them a little helps to get them in securely
Use a small croc/alligator clip as a heatsink to avoid heat damage like this
Hi Ian
All your values look correct and everything appears to be orientated the correct way
I can’t clearly see how your DC jack is wired but with your LED lighting up I’d think that’s ok
Your trimmer and R20 can’t be seen clearly
Trimmer should be code 104 yours looks like it’s missing the top white plastic part?
The only other thing we can’t see is your jumpers under the MN3007 if that’s all correct it sounds like you may have a dry or poor solder joint, post a picture of the solder side of the pcb, are the back of your pots insulated from shorting on anything on the solder side of the pcb
Where did you get your MN3007
A lot of work in that Paul nice combo
Your labelling looks fine not too far off
I’ll usually plan, measure and drill my enclosure then print off my labelling on paper until it lines up exactly
I lay the paper onto my enclosure and poke a pen through the holes to see how it lines up also placing my knobs of choice etc on it to make sure they don’t obscure anything
Have you reflowed all the solder joints from 9v to R3 the bias pot Q1 C2 and R4
What are your voltages on all transistor pins and what voltage is your power supply putting out
Heres a PDF Paul should explain it and it’s use etc as Cybercow says you don’t have to build a big fancy gizmo you can rustle up the one shown very quickly and get the job done
https://drive.google.com/file/d/1T9OsJ0riQhm1QFWPfNQ5q5guikuFKDRN/view?usp=drivesdk
Check the bias pot changes resistance as you turn it Tim it’s wired as a variable resistor so the pot along with R3 bias the transistor
Place your meter probes on lugs 1 and 3 and resistance should alter as you rotate the pot
Terry set your meter to 20V DC place your black probe on ground and red probe to the drain pin on the left nearest to the 3PDT
Looks to me like your in T for tip pad is going to the ground lug on your in jack (black wire) and your red wire goes from the in ground pad to your BI pad but it’s very difficult to see I can’t really see the out pads but again you may have those wired incorrectly if your black wire is ground that also looks like it goes to the out T pad
If you look closely at the pcb in and out pads one pad has a small T for tip the other is for ground
Your in and out T for tip wires should go to BI and BO on the 3PDT pcb
