Need Help Repairing AC Fried Fuzz Pedal

[fenderguy81]

I am helping a friend repair his boutique fuzz pedal that accidentally had 10v AC power run through it for a very short time. It calls for 9v DC and now after being exposed to the AC voltage, is making a loud squealing sound. The pedal still powers up and functions to some degree, but obviously needs to be fixed. I am not as familiar with repairing pedals, but I have made some minor repairs on guitars, Mic power supplies, and amps. I know how to solder and I have a multi-meter. Can anyone point me in the right direction as far as testing or troubleshooting which part likely failed first? I have attached a few photos of the pedal for reference. Any information would be greatly appreciated!

Thanks!

[antonis]

I should start with electrolytic caps replacement..
(althought "squeal guilt" is often an open NFB cap..)

[fenderguy81]

Thanks for the info! I was hoping I would see a "pimple" on any caps that may be leaking/damaged, but hopefully replacing these caps will fix the issue. I'll go ahead and order some replacements and start there and report back.

Thanks!

[fenderguy81]

So I am still having trouble with this pedal. It is a fuzz pedal with a "glitch" delay/repeat function. I went ahead and replaced all of the electrolytic caps and the IC. When the pedal is ON, it is making and idle clicking and buzzing/hissing sound. In addition, I am getting a low signal when the pedal is bypassed. Any suggestions would be really appreciated.

Thanks!

[Slowpoke101]

Measure the voltage between pins 1 and 3 of the IC - which appears to be a PT2399 delay. You should read very close to 5V. Let us know if what you find.
Is there any chance of posting a few pictures of the underside on the board?

[fenderguy81]

Thanks for the response! I attached a few more pictures of the underside of the board. Also, I got 4v when I measured the top pin 1 and 3 of the IC PT2399 chip.

UPDATE: I retested the pedal and the clicking sound is still there. It's like ticking of a clock that gets faster/slower when I adjust the bottom left pot (time). The click is there even when the pedal is bypassed.

[Slowpoke101]

Good pictures. That does answer a question I was wondering about.
4V is very low. Take the IC out and measure the voltage between pins 1 and 3. If it goes up to 5V - good. If it is 0V measure between pins 1 and 4. You are looking for 5V.

Next, have a look at what appears to be a transistor (3 legs ). This most likely a 78L05 regulator. The leg closest to the IC should be at about 9V (depending on your power supply ), the middle leg should be 0V and the remaining leg should be about 5V. If your results are different then it is possible that the regulator has been damaged by the AC accident - not unusual.

Edit: Made an oops with the regulator pin voltages. Corrected now.

[fenderguy81]

Thanks for the reply Slowpoke101, I am having difficulty testing the IC. I have never tested these kinds of components before so I just want to ensure it's not user error. I purchased 4 new PT2399 IC's and replaced the IC that was in the board. I am trying to test a new IC to make sure I am testing it correctly and I cannot get 5V when the chip is out of the circuit. I set my multimeter to DCV and used the multimeter probes on pins 1 & 3 and got 0V. I put it on 1 & 4 and also got 0V. Am I doing this correctly?

Also, can you please elaborate a little on how to test the V of the transistor? What should I set my multimeter to and where should I put the probes? Also, does it matter if the pedal is on/off and should the component be removed from the circuit board to test it? It is a 78L05 transistor (LM78L05ACZ).

In addition, I read that the diode could easily be damaged from the AC power accident. I went ahead and removed the diode from the board and unfortunately had to clip the leads to get it out so I cannot put it back in. It's a 1N4001. Would it be ok to replace this with a 1N4007 diode as that is all I have on hand or should I just order the 1N4001?

Sorry I am pretty new to all of this. Thank you so much for taking the time to help troubleshoot this pedal!

[Slowpoke101]

Trying to test an IC out of circuit is difficult at best. Testing a chip with a multimeter doesn't really tell you much. The best way is to measure the voltages on each of the chip's pins whilst it is in circuit and powered. Pin 1 of a PT2399 should be 5V. Pins 3 and 4 are usually at 0V and quite often connected - these are the Analogue ground and the Digital ground.

Your multimeter should be set to the 20V DC range unless its an auto-ranging meter in which case it should be set to DC Volts.

The transistor looking device is a 100mA 5V DC regulator. To test it just measure the voltage on each of its outer pins. Connect the meter's black probe to 0V somewhere - try the DC power connector. Use the red probe to test the voltage on each of the regulator's outer legs. One should be at a bout 9V and the other leg should be 5V.

The 1N4001 diode can be safely replaced with a 1N4007 diode. The 1N4007 as a much higher voltage rating than the 1N4001 which in this application is not important.

There is no problem with being new to all this (we all were at some point ). Plenty to learn and fun to be had.

[willienillie]

The only "Q" is a regulator, and the only IC is a PT2399 delay chip.  What makes the fuzz?

[PRR]

> I cannot get 5V when the chip is out of the circuit.

The chip gets power FROM the circuit.

Like a 120V lamp. Take the lamp out of the 120V socket, you won't find 120V on it anywhere.

In context, you need to find 5V *in the circuit*. As Ian says, this comes from the "transistor looking device". It gets about 9V from external power and regulates it to 5V. If the pedal has been mis-connected to AC, this regulator may be dead. Per Ian's instructions, with black probe on pedal ground (audio jack shell), and properly connected 9V supply, you should expect +9V, +5V, and zero V on its three pins. If you have 9V and 0V, but the third pin is not 5V, it may be fried.

[fenderguy81]

Thanks for the responses and helping clarify everything. I tested the transistor and got 9v on pin 1 (emitter), 0v on pin 2 (base), and only about 1.8v on pin 3 (collector). I tested pin 1 on the IC and got around 1.8v as well. Correct me if I'm wrong, but it sounds like the transistor got damaged and isn't putting out the proper voltage (5v) to the IC, which I'm assuming is probably what slowpoke101 and others were susupecting. It looks like I'll have to replace the transistor. Is there anything in particular I should be aware of when ordering the transistor or would it be ok to replace it with any 78L05 transistor? I was planning on placing an order with Digikey or Mouser unless you guys have any recommendations for a better place to get parts from. Also, should I order anything else for this pedal while I'm at it? Is it likely that any of the non-electrolytic caps or resistors were damaged?

Also, regarding the question about it only having 1 "Q" and being a fuzz--the manufacturer calls it a "Super Weirdo: glitch super fuzz time modulation unit." I wish I could offer more information about its classification, but if you're curious to hear what the pedal sounds like check out some demos on youtube. It's a pretty cool sounding pedal and the glitch feature seems like it'd be a lot of fun to play around with.

Thanks again guys!

[Slowpoke101]

You have made some progress. This is good.

1.8V is obviously far too low and I think we can safely say that the regulator has failed. Whilst the device looks like a transistor it is most certainly not. It is a +5VDC 100mA Voltage Regulator in a TO-92 style package. It is actually a linear  integrated circuit (IC ). If you have a look at Mouser or Digi-key for a 78L05 your search result will show quite a few different types - confusing.

Smallbear has exactly what you are looking for;
http://smallbear-electronics.mybigcommerce.com/ic-78l05/

You may have a local supplier that has one in stock. The IC is quite common but that also depends on where on Earth you are.

By the way, the pins are not called collector, base and emitter. They are simply IN (Input, 9V in your case ), GND (0V or Ground ) and OUT (Output, +5V ). Regulators are available in a large variety of output voltages.

It is unlikely that any other components have been damaged but keep an open mind with this. It is also possible that the 78L05 saved the original PT2399 - you may want to test it after you replace the regulator.

The pedal's fuzz ability from such a low component count unit is interesting. I suspect that it makes use of the PT2399's sensitivity to being easily over-driven by an input signal.

[patrick398]

Be sure to get the 5v regulator in the TO-92 package not the TO-220 package, i bought a load of the latter when i was first starting out and they're often too big to fit on circuit boards calling for a 7505.

I've had some unintentionally fuzzy pt2399 circuits and never really liked the way it distorts, interesting sounds though. What's the name of this pedal?

[Slowpoke101]

Be sure to get the 5v regulator in the TO-92 package not the TO-220 package, i bought a load of the latter when i was first starting out and they're often too big to fit on circuit boards calling for a 7505.

Very good advice. An easy trap to fall into.

The pedal is a JPTR FX Super Weirdo. Have a look here; https://www.jptrfx.com/pedals/
They have some "interesting" effects by the look of it.

The effect appears to be similar to what is described in this thread https://www.diystompboxes.com/smfforum/index.php?topic=87493.0 , particularly on the last two pages.

[fenderguy81]

Thanks for the prompt responses! I went ahead and ordered the transistor regulator on Small Bear per Slowpoke101's link. Thank you for the link! I live in Southern California and unfortunately, after RadioShack went out of business, there doesn't seem to be any stores around here that carry parts. I'll report back as soon as I receive the part and get it in the board.

Thanks!

[fenderguy81]

Ok so I just got the new regulator soldered in and tried testing the pedal. When the pedal is on, the volume drops significantly and there is still idle "mechanical" noise. I tested the new regulator and got 9v on pin 1, 0v on pin 2, and only 1.3v on pin 3. The first pin of the PT2399 also was showing 1.3v. Should I try changing the other caps or resistors at this point?

Thank you!

[R.G.]

 Having AC power - even at only 10V - hooked to a pedal is one of worst things that can happen to the pedal. There is a good chance of killing or crippling every semiconductor and every polarized/electrolytic capacitor.  One really bad aspect of this situation is that things may be left dying but not dead, so you can wind up figuring out and fixing what you think is wrong, only to have something else fail a short time later.

It's good to decide whether you can live with fixing one thing at a time if necessary as they fail, or instead have to make the pedal be reliabnle without you repairing it again. If it's the latter, here is my prescription for fixing it:
1. Replace all the polarized/electrolytic caps. They're cheap, and likely to have been damaged by the AC. Sure, you'll replace some good ones. OK, fine.
2. Replace the semiconductors. This includes the regulator you've already done, the reverse-protection diodes, transistors and ICs. This is modestly expensive, but when diodes and transistors cost pennies to dimes, regulators cost $0.50, and a PT2399 costs a few dollars, it's probably worth it if you value your time at all.
3. If there are custom programmed parts like PIC controllers and/or EEPROM memory there, call the manufacturer and try to source new ones. This may well be cheap enough to do.
Once you've done these, or at least 1 and 2, you can do any remaining troubleshooting needed. It will be much faster than reasoning out symptoms for multiple failing parts.

I'm not a proponent of just throwing in parts to fix things, but in a very few cases - like AC power supplies - it can make sense if done with a proper plan.

[ElectricDruid]

My most popular screw-up* is fitting those LM78L05 regulators back to front. Whereupon they don't work and the circuit doesn't work. Luckily for me, it doesn't seem to harm them, and when you swap them the right way around, everything springs to life.

HTH,
Tom

* Ok, I lied. One of my most popular screw-ups....

[fenderguy81]

Thanks for the responses. I have already replaced all of the electrolytic caps, the regulators, and the diode. Other than the pots and switches, the only things left would be the resistors and non-electrolytic caps. I guess I should probably try replacing the remaining caps at this point and then the resistors thereafter if the problem persists. I am not familiar with these caps. Can anyone clarify what type of caps they are and maybe a good place to source them from? They read as follows:

WIMA 3300 250-
WIMA 0.01 630-
WIMA 0.22 63-

Thanks!