Mystery of the Tone Virus

[Pauleo1214]

Hello all,

I started building pedals this year and have 50 successful builds under my belt and I would venture to guess 15 or so where I made mistakes. I bought a Tone Virus as I wanted to build a combo pedal with a tremolo for a choppy, synth sound.

My first attempt was partially successful. I was getting square wave fuzz but high pitched squeal on the oscillation knobs from the mixer. Replacing all the IC chips produced no discernible difference. I bought a second board and finished wiring it up. It worked as it should upon firing it up however the LED did not power up despite testing good with a disc battery. I took the board out of the enclosure, rewired the LED and popped the whole thing back in. Now there is no signal and a putting sound from the oscillator.

I guess third time's the charm but I'd rather figure out what's going on with this board given it was working the first time around. Any help would be greatly be appreciated.

A follow up question, would anybody be interested in taking this in to troubleshoot and solve? Please PM if interested.

[madbean]

Looks like you have the wrong value in all your 1k spots. Those appear to be 1M, not 1k.
You've got a couple cold joints on the toggle switches, but you just need to reheat them a bit is all.

[Pauleo1214]

I replaced R2 and R19 as well as reflowed the solder joints on the toggles. The same issue persists still.


The wrong value components in R2 and R19 would not explain why the unit functioned fine and then conked out. Here is a video of the board and the issue.

https://youtube.com/shorts/suaTGtAzm_k

[madbean]

Hmm. That cycling sounds like a power issue. Have you checked your voltages? Start with measuring the VC (IOW see what you've got on IC1 pin8). Also, check VB (pin5).

[Pauleo1214]

Apologies for the late reply. I am getting some far out readings.

IC 1 Pin 1 is 17.3v
IC 1 pin 5 is 12.3v

What do you make of it?

[madbean]

Something is not right there. You either are not using a 9v supply for power or you've measured the voltages incorrectly. Make sure you black lead on your multimeter is going to ground. You can use the "GND" pad on the bottom left of the board.

[Pauleo1214]

My apologies, I had my multimeter on the wrong setting.

I am getting
1.73 volts on Pin 1 IC1
0.65 volts on Pin 5 IC5

[madbean]

You still haven't listed your VC voltage (pin8) but that's enough to see something is wrong with the power. So, there's an easy process of elimination to start figuring out where the problem is.

Start with this - take out all the ICs but IC1. Check pins 8 and 5 again and compare your readings to the ones listed in the doc.

(1) If they are not a match, take out IC1 and measure the same voltage in the socket without the IC. If they match, the problem is IC1. If they still don't match without IC1 then something has gone wrong in the power supply chain.

(2) If they are a match, then continue to put in the other ICs in one by one, each time looking again at the voltage readings on pins 8 and 5 of IC1. If loading one of the other ICs causes those voltage to suddenly change, then that narrows down the problem area.

[Pauleo1214]

Thank you. I will follow your guidance and see what comes.

[Pauleo1214]

It looks like something is wrong with the power supply. I did remove all the ICs except IC1. The voltage in pin 8 was 0.65V. I removed IC1 and measured the voltage the same voltage in the socket.

Do you recommend replacing all the components downstream in the power supply?

[madbean]

Since you have D1 socketed I recommend removing that first and rechecking the VC voltage. If that diode is damaged somehow it could be shorting. If you still have a bad voltage reading after removing D1, then take a very close look at all the solder joints on the bottom. Look for any solder bridges. Even a very tiny bridge can create a problem. Reflow any solder joints that look suspect.

[Pauleo1214]

Took out D1 and still got the same voltages. Reflowed all the joints and am now getting 8.72V on pin 8 of IC1 but 0.24V  on pin 5.

I think I might rig up an audio probe and start testing components.

[madbean]

That's excellent progress. Your problem now seems to be with the VB voltage. You should be reading about half of your measured 8.72 VC but you are barely above 0. The VB voltage is created by the voltage divider formed by R22 and R23. From your build pic, you've got the correct values in that spot.

I would start by reflowing the solder joints associated with these components:
R3
R22
R23
C16
IC1 pin5

If you have a continuity cheacker on your multimeter, make sure pin5 does not have continuity with pin4 or pin6 of IC1.

Keep at it - you almost have this solved.

[Pauleo1214]

I reflowed the solder at those joints. I also checked for continuity on pins 4-6 on IC1; no continuity.

Unfortunately I still get the same 0.24V at pin5 and 8.72V at pin8. Should I maybe replace all the components listed in your post?