Debugging OCD overdrive tayda pcb

[Shaneb1987]

I'm having an issue with the ocd overdrive from tayda, Jack's working fine in bypass but no sound when switched on. If anyone can help me out with this that would be great

Measurements:

Battery: 9.11V

Q1 2N7000
S: 2.194V
G: 2.191V
D: 4.40V

Q2 2N7000
S: 4.40V
G: 4.41V
D: 4.01V

IC1:
1: 4.40V
2. 4.40V
3. 4.20V
4. 0V
5. 0V
6: 8.09V
7: 8.21V
8: 8.76V

[r080]

Welcome to the forum!

Pins 5, 6, and 7 of IC1 look suspicious.

Nothing specific stands out from the pictures at the moment, but there are some areas that look a little rough, and might be worth checking for solder bridges.

[idy]

Yep, pins 5,6,7 are off. They should be like 1,2,3.

This circuit sends mid point bias to pin3, and that same V comes out pin 1. It should reach pin 5 but it doesn't, instead you have 8v. There are two resistors, R6 and R7 in between. (and the clippers). What are the volts on each side of those two Rs?

Double check values of those two Rs. With power off you should be able to test them with a meter. Read the color bands? No values on the schematic, they should be 10k.

[idy]

The killer is 0v on pin 5. Check for short to pin 4 (which is supposed to be 0.)

Your voltages on the MOSFETs are confused, but they are just clippers and cold be removed to leave you a cleanish booster (until you reach opamp clipping.)

Both Qs have G and D connected, S separate. You need to see the same voltage on G and D. Maybe mixed up pins?

[Shaneb1987]

Hi everyone, thanks for the replies on this, I did find a link on pin 5 to ground, looks like a bit of the pcb track was exposed and came into contact with it. Although now I'm just getting a high pitched whine with no signal getting through from the guitar. The whine can be controlled with the pots.
New values from the IC and mosfets are
Measurements:

Battery: 9.06V

Q1 2N7000
S: 4.28V
G: 4.28V
D: 4.37V

Q2 2N7000
S: 4.37V
G: 4.37V
D: 3.99V

IC1:
1: 4.39V
2. 4.36v
3. 4.23V
4. 0V
5. 4.28
6: 4.35V
7: 4.37V
8: 8.64V

I can't see any more solder bridges and resoldered all joints, could this be a faulty component?

[idy]

good work, you found a fault and now your voltages all look OK.

Obviously there is something else. Best course is make an audio probe and start poking around. Signal should come in op amp pin 3, out 1, in 5, out 7. Where does the sound die? You can find out.

[Keeb]

I would start with making sure that your ground on the PCB is connected to signal ground. Take your DMM and check continuity between the ground pad on the PCB and the sleeve on of the jacks. If you don't have a connection then I would add a wire between sleeve and the negative terminal on the DC jack. Otherwise do what idy suggested.

(I tried to follow your wiring and it seems to me that the board is only grounded to the DC jack while the guitar jacks are grounded on the switch but the two are not connected to each other)

[Shaneb1987]

Thanks for the replies 👍🏼 I've checked the grounds and they are all good, it's messy but I have wires looped around to ground the Jacks, switch, power socket and board. I'm going to make up an audio probe later on and see if I can find where the fault is.

[antonis]

Although now I'm just getting a high pitched whine with no signal getting through from the guitar. The whine can be controlled with the pots.

Although it should be more than this, check for open C3..

[Shaneb1987]

Think I'm making progress, I've checked c3, it seemed fine but switch it out anyway (just incase). I've made up an audio probe and I'm not getting noise from the input side, I'm getting noise on the v2 side of r3 but not the other side, or anything else connected to pin 3 of the IC.
I'm getting noise on everything after pin 3 so I'm thinking I have my input grounded at the switch. I'm going to redo the switch later on and see how that goes🤞

[Keeb]

Think I'm making progress, I've checked c3, it seemed fine but switch it out anyway (just incase). I've made up an audio probe and I'm not getting noise from the input side, I'm getting noise on the v2 side of r3 but not the other side, or anything else connected to pin 3 of the IC.
I'm getting noise on everything after pin 3 so I'm thinking I have my input grounded at the switch. I'm going to redo the switch later on and see how that goes🤞

Nice to see you making progress!
Your switch wiring seems correct. It grounds the PCB input when in bypass mode (nothing wrong there) but should work properly (and you having a guitar tone in bypass seems to prove that).
Please measure before redoing the switch (3pdts can be quite fragile when de-resoldering). Use continuity mode and check between the PCB in and ground, flip the switch and expect to hear a beep in bypass!

Edit: I would verify all ground connections with a DMM (a wire does not mean a connection!)

[Shaneb1987]

Hi Guys, I made up an audio probe. Tracked the circuit and found the volume and tone pots are faulty. I checked a few more in the bag of them I got and found several of them Not working. Must have been a dodgy batch. I've replaced the 2 pots and we have a working overdrive. Thanks very much for your help guys, couldn't have doned it without your help. I'm happy it's working but even happier with a few extra troubleshooting skills. Thanks again