Troubleshooting IC BMP Build

[wimacfee55]

Long Time Lurker, first time poster. I hit a wall troubleshooting a IC BMP build and I followed the debugging guide post as close as possible:

Also, thanks for all the help that's on this forum. It's one of the best things I read each day.

1.Name of the project: EHX IC Big Muff V5 '78 as done by Tagboardeffects

2.Links to the source of the project web site with the schematic or project, layout and wiring diagram: https://tagboardeffects.blogspot.com/2013/12/ehx-ic-big-muff-v5-78.html?showComment=1540813326822#c282828169989013548 with a similar circuit that I've used for understanding here (the 1978 OpAmp ciruit) http://guitarpedalbuilders.blogspot.com/2012/06/1977-1978-big-muff.html. Quick note, for the Veroboard, I denote the upper right hand corner spot as A1, and the bottom right hand corner as R20, the letters are the Y axis, the numbers the X axis.

3.Some candid admissions about how closely you followed the suggested layout, if any. If you just perfboarded it, say that, and if you can, include a picture of the board: I have used a vero strip board, multiple photos included for inspections for shorts, bad solder joints, etc.

4.Any parts substitutions or modifications you made to the original. I followed the suggested chips and diodes closely and matched the pinouts: minor substitutions for caps where it was near enough. For example, I subbed a 1.2K resistor for a 1K resistor in a spot. All electrolytic caps were matched to the value requested.

5.Whether or not it's a positive ground circuit like a PNP fuzz or a Rangemaster that has been hacked to work with negative ground: not the case, negative ground.

6.What it does and does not do how it works: Works in bypass with no issues. When the effect is engaged, the typical sound is as if it is still in bypass, then it cycles through a few different sounds, from a faint and distant fuzz, to the expected roar. Sound is making it through, just intermittently. I verified the jumpers between strips are current and the cuts in the stripboard are correct by using a continuity meter. I verified component placement and made only minimal swaps. I used an audio probe to trace it from the input, and while I get a strong signal at pin 1 of the JRC 4558, I get a faint sound at pins 5 and 7 of the chip before it goes off to the sustain pot. I also triple checked for shorts across the Veroboard to attempt to catch anything there.
Voltage list: Power supply: 11.6V (Boss 9V wall wart)
JRC4558 Pin 1: 5.65V
Pin 2: 5.67
Pin 3: 5.62
Pin 4: 0.1mV,
Pin 5: 1.14V,
Pin 6: 1.41V,
Pin 7: 1.48V,
Pin 8: 11.2V
UA741CP Pin 1: 3.5mV,
Pin 2: 6.1V,
Pin 3: 5.85V,
Pin 4: 0.1mV,
Pin 5: 3.5mV,
Pin 6: 6.4V,
Pin 7: 11.2V,
Pin 8: 0.04 to 0.08V varying as I measured it over 2 minutes

[PRR]

> JRC4558
> Pin 1: 5.65V
> Pin 5: 1.14V

These two should be essentially the same. Something is leaking here.

[antonis]

I pressume drops (about 20μA each one) are protons, due to their leakage direction.. 

[wimacfee55]

Thank you PRR! This is a step in the right direction. I measured the voltages leading up to the 47K resistor and the 4.7nF cap.

One quick note about a difference between the veroboard and the circuit, the veroboard has no direct link to connect Pin 5 and Pin 6.

Perhaps the leakage is from that 10nF cap going to ground? That's the only other component on that strip (G11 to G20)

[duck_arse]

wimacfee55 - seeing as no-one else has yet, welcome to the forum.

the drawing convention used on your dia suggests a "connection" is made between lines only where a dot appears. you don't want any connection between pin 5 and pin 6.

[edit: ] a closer look at your board shows what appears to be a shorting link between pins 5 and 6. snip it out, remeasure yr voltages.

[wimacfee55]

Thank you duck_arse, it's a pleasure to be here!

Yes, I originally made that connection and snipped it, the resolution on the photo doesn't quite show it, but theres ~3mm between the snipped ends. The voltages I have listed are still what I'm seeing. When I get back from work today I'll desolder those pieces and replace the 10nF cap that's there on the strip with pin 5

[wimacfee55]

That 10nF cap to ground was the culprit! I replaced it, removed the snipped link and it roared to life. Thank you so much for the help everyone!

[wimacfee55]

This Pedal is back to cause me more grief, I'm getting almost no signal at the output.

I've traced it with an audio probe, and I lose the signal after R10 (8k2, after the second leg of the sustain pot). At leg 3 of the sustain pot, I don't have much of a distorted signal after the JRC4558, the signal is quieter than the input of the JRC4558 at pin 2.

I've replaced the greenie caps that caused the issue before, and I remeasured the Pin Voltages:
Power Voltage: 11.4V
JRC4558 Pin 1: 5.54V, Pin 2: 5.54V, Pin 3: 5.48V, Pin 4: 0V, Pin 5: 5.25V, Pin 6: 5.30V, Pin 7: 5.4V but varies with time, Pin 8: 11V
UA741: Pin 1: 0, Pin 2: 1.98V, Pin 3: 0.1V, Pin 4: 0V, Pin 5: 0V, Pin 6:3.34V, Pin 7:11V, Pin 8: 0.1V

As always, thank you for the help. If this winds up being a ghost in the machine again, I'm just getting the PedalPCB board for it...

[wimacfee55]

Figured it out! Cold solder joint on pin 8 on the UA741. Thank goodness I posted the voltages here before, my records are not so good in the old marble journal

[duck_arse]

not to rain on your parade or anything, but pin 8 on the 741 is not connected to anything in that circuit. unless you've modded it [?] and then, still, probably not a thing. are you sure of your part/pin references?

[wimacfee55]

Now that you mention it, you're right about pin 8. I didn't mod it from the tagboard layout, and I did re-solder each of the UA741 socket pins as well as each component in the audio probe trace. I'm going to add re-soldering each joint as a troubleshooting step for next time and not trust my eyes for cold solder joints.