Phase II LFO issues

[thabigburrito]

Hi everyone,
I’ve recently taken on a few builds, the most complicated being a phase II and (unsurprisingly) being the one with issues. Signal bypasses fine. When on, the indicator lights, the yellow LED turns on but does not vary in brightness, and the signal cuts. Playing very loud, I can get a fuzzy gating sound to come out, like a super misbiased fuzz pedal. There is also a significant amount of 15-17k oscillation hitting my interface (made troubleshooting that much more grating), but I'm not sure if that’s normal or not. Any advice would be much appreciated, thank you guys.

 

[thabigburrito]

Update: the voltage regulator gets really hot when the pedal is on, and there is 0 volts at vOut. Should I try a new chip? All the op amp voltages check out.

 

[Robert]

Is that resistor lead touching pin 5 of the TC1044 by any chance?

 

[thabigburrito]

Is that resistor lead touching pin 5 of the TC1044 by any chance?

View attachment 31856

No, that was just the LED resistor that I temporarily disconnected as I had set it up to pulse with the lfo. Wanted to check if it was causing problems but it is currently resoldered.

 

[fig]

Right above that…any solder bridge here?

 

[Diynot]

Is that resistor lead touching pin 5 of the TC1044 by any chance?

View attachment 31856

Shouldn’t the end of that lead be attached to the pad under it, is that resistor even in circuit? Looks like it might have broken off

 

[Deperduci]

he said it was the LED resister, the LED has more of an effect.. I'm with fig looking at a possible jump between the output sleeve wire and a leg of the pot but that might be a flux residue, is the flux semi conductive? vigilante said he had such issues with the flux core in 1 brand's particular line... . what's happening under the 470nf film caps? did a lead get bent and arcing to a resistor? doubt the power in wire is currently causing issues but that looks ready to break as well. take the IC's out, rub it down with some IPA on a cheap toothbrush(like you'd get to use on a dog) and see if it does the same thing once it's dry and chips back in.

 

[Synchrony Pedalworks]

Just based on the picture, and without good electrical knowledge, could R45 and C19 be bridged?

 

[thabigburrito]

Shouldn’t the end of that lead be attached to the pad under it, is that resistor even in circuit? Looks like it might have broken off

There is a mod where you attach the other lead of that resistor to pin 3 of the depth pot so that the indicator led flashes with the lfo; I took it off in case it was causing issues.

 

[thabigburrito]

he said it was the LED resister, the LED has more of an effect.. I'm with fig looking at a possible jump between the output sleeve wire and a leg of the pot but that might be a flux residue, is the flux semi conductive? vigilante said he had such issues with the flux core in 1 brand's particular line... . what's happening under the 470nf film caps? did a lead get bent and arcing to a resistor? doubt the power in wire is currently causing issues but that looks ready to break as well. take the IC's out, rub it down with some IPA on a cheap toothbrush(like you'd get to use on a dog) and see if it does the same thing once it's dry and chips back in.

Thanks for the advice! The 470nf’s sit on top of other components because they are so big but i am not measuring any continuity between them and the other components. And you’re right about the power in, i had to soldering in leads because i got the wrong power jack on accident. I will try cleaning the board and see if it helps, and i have a new 1044 on the way.

 

[thabigburrito]

Update: the board is clean and certainly looks a lot nicer; contact cleaner in the ic sockets. Unfortunately, no dice. Vout on the TC1044SCPA is still 0 v, and all i hear is 17k when the effect is on. Weirdly, the boost pin of the IC is receiving 9v, so it should be operating at 40khz+. Maybe the oscillation is not coming from the IC or it suggests a faulty one, not sure. I made a probe but it gives me nothing past the basic input stage.

 

[fig]

Vout = 0v with the new charge pump?

Oh, probably not already,

 

[MichaelW]

Just taking a stab at this but I noticed you're using a spring clip type IC socket for the 1044. I recently had to get some overnight from Amazon because I was short a few of the machined ones I needed for a build. (ironically, it was my Phase II build, and it needs a bazillion sockets!) My point is that the legs on those things are pretty flimsy and can easily bend, I caught myself inserting a socket and one of the legs was bent under the socket (but still managed to poke through the hole somewhat).

If you're replacing the 1044, you might want to sacrifice the socket as well and snip It off and have a good look underneath it for shorts, solder pools, etc.

 

[thabigburrito]

Ok, I installed a new socket and got a couple new 1044s, having the same issue. About -.2v at the output of the chip, high frequency noise through all of the op amps to the output. Would it be helpful if I posted voltages? I’m fairly stumped on this one.

 

[MichaelW]

Ok, I installed a new socket and got a couple new 1044s, having the same issue. About -.2v at the output of the chip, high frequency noise through all of the op amps to the output. Would it be helpful if I posted voltages? I’m fairly stumped on this one.

Yah I think it would help to post voltage of all pins of your 1044 and at least IC1.
If you're not getting the correct voltage out then it has to be something upstream of that.
I can't see D6, it's hidden under the cap, but is it oriented correctly?

 

[thabigburrito]

I replaced the electrolytic caps just in case, as they are mostly in the voltage regulator circuit, no luck. Some voltages below.
IC 7 1044SCPA
1 BOOST: 8.87
2 CAP+: 3.54
3 GROUND: 0.00
4 CAP-: 0.703
5 vOUT: 0.10
6 LOW VOLTAGE: 4.40
7 OSC: 7.35
8 V+: 8.89

IC1 TLO72
1: 8.12
2: 4.79
3: 0.00
4: 0.10
5: 0.88
6: 1.41
7:1.45
8: 9.01

 

[fig]

I’d check continuity between socket springs and solder tits. As Michael suggested, those spring socket pins bend under extremely easily.

 

[jimilee]

I’d check continuity between socket springs and solder tits. As Michael suggested, those spring socket pins bend under extremely easily.

Solder tits....

 

[thabigburrito]

Continuity checks out. Man, this feels like the last tube amp i built. Obsessing over a noise issue for weeks, turns out to be a bad preamp tube.
If the problem is principally with supplying negative voltage, can i rule out anything downstream of the regulator’s circuit for now or could it have an effect on the operation of the chip?

 

[thabigburrito]

Update: I'm measuring a direct short (double-sided) between pin 5 of the regulator (-9v out) and ground. Is this expected? The short measures between the two pads of C18 with anf without the cap installed. Also, measures between the ground pins of the op amps, which should be on the -9v rail, and ground. I think this is the big issue. Any ideas?