another sunking problem

[rhinson]

Indeed, that's what I thought. But, the proof is in the pudding.

I have a few CP's on hand so I'll compare. Could be the first two are just crap.

it's funny because i have jrc brand tl072's in one build and t.i. brand tl072cp's in the other and they both do the same thing (although the voltages in one are not off to quite the same extreme, it still has the same symptoms of the gain pot affecting the voltages in the exact same fashion).   i also have 2 different brand change pumps,  some of the electrolytics are different brands in each, most resistors are from the same batch but a few are not.   the only constants are the panasonic film caps and the one tant. ---actually one of the film caps in one build is not panasonic, but all the rest are.   even the dual 100k's are different (one is solder lugs from smallbear and the other is pcb lugs from somewhere else.    i'm just looking for some place to start in terms of troubleshooting, given the symptoms and going under the assumption the board is good. my first/only instinct so far was to check the 2 1uf caps between ic 1 and ic but they both seemed to be doing their job.      given all the interconnections here,  i'm a little lost on what to check, and it still seem odd that both builds do the same thing.    rh

[oldhousescott]

The DC gain of the IC2B stage is -1, so pin 7 should follow pin 1 in an inverse relationship centered around 4.5v, which it seems to be doing, so I'd say that stage is correct.

If you disconnect GAIN1 and GAIN2, IC2 pins 1 and 7 should go back to 4.5v. IC1 pin 1 should be 4.5v and pin 7 should go to 4.5v, although it may drift.

Check that C16 is inserted correctly. It's upside-down from all the other polarized caps (except for C15 of course).

I'm still trying to wrap my head around how pin 1 of IC2 can go below 4.5v under static conditions. Can you post the voltages for all the pins on IC1 and IC2?

[rhinson]

The DC gain of the IC2B stage is -1, so pin 7 should follow pin 1 in an inverse relationship centered around 4.5v, which it seems to be doing, so I'd say that stage is correct.

If you disconnect GAIN1 and GAIN2, IC2 pins 1 and 7 should go back to 4.5v. IC1 pin 1 should be 4.5v and pin 7 should go to 4.5v, although it may drift.

Check that C16 is inserted correctly. It's upside-down from all the other polarized caps (except for C15 of course).

I'm still trying to wrap my head around how pin 1 of IC2 can go below 4.5v under static conditions. Can you post the voltages for all the pins on IC1 and IC2?

the rest of the voltages are not affected by the gain pot and are consistent with the voltages on my 2 good builds from the bajaman layouts i etched.   

ic1    pin1    4.6      pin8    9.5                          ic2    pin1(problem)         pin8   17.2
        pin2     4.6     pin7 (problem)                            pin2 4.6                 pin7  (problem)
        pin3    3.7      pin6  4.6                                    pin3  4.6                pin6  4.6
        pin4    0         pin5  4.6                                    pin4  -9.1              pin5   4.6

also it's not pin 1 of ic2 that goes neg.,  it's pin7.    pin1 goes from 8.8v to 12.6v, and pin7 goes from0.6v to -2.9v  (both happen together at the same time as the gain pot is rotated from min to max.).   thanks for thinking about this for me.   i'll take any assistance.     rh

[oldhousescott]

OK, I'm guessing (hoping) the IC1 pin 3 reading is a typo. That should certainly be 4.6 like pins 2 and 1.

Anyway, IC2 pin 1 going positive kind of makes sense if IC2 is operating correctly and there's a short earlier in the circuit. I would still recommend checking the three 1uF caps to make sure they are installed with the correct polarity.

[rhinson]

OK, I'm guessing (hoping) the IC1 pin 3 reading is a typo. That should certainly be 4.6 like pins 2 and 1.

Anyway, IC2 pin 1 going positive kind of makes sense if IC2 is operating correctly and there's a short earlier in the circuit. I would still recommend checking the three 1uF caps to make sure they are installed with the correct polarity.

yes i've double checked cap polarity on both boards (remember i've got two sunking boards doing the same thing) and all is installed correct.   and no the ic1 pin3 is not a typo.  as a matter of fact,  it's also the voltage i get on my other 2 successful builds on entirely different boards/layouts (bajaman) so it must be biased that way on purpose.   rh

[oldhousescott]

Oops, 3.7 is reasonable in this instance. The meter is loading the circuit.

Maybe check the voltages at the junctions of C16/R19 and C10/R16.

[Doc Plus]

I just built one and tried it quickly, and it works fine. I used TL072CN and MAX1044.
All the parts comes from smallbear.

[madbean]

I've built up a new board, as well, from the same batch that's been shipping the past few weeks. Mine fired up right away and is behaving. The only sub was 1n60 for the germanium diodes. I'm not sure if I like those there....I think 1n34a or 1n270 "felt" a little better to me. I'm going to do a side by side with other other build to compare.

Anyway, here are the voltage readings on my new build, which are pretty much in line with the previous. I used a TC1044 and TL072CN as in all the previous builds I've done.

IC1
1 4.45
2 4.47
3 3.43
4 0
5 4.45
6 4.46
7 4.45
8 8.88

IC2
1 4.52
2 4.47
3 4.46
4 -8.46
5 4.45
6 4.46
7 4.41
8 16.03

IC3
1 8.88
2 4.55
3 0
4 -4.15
5 -8.47
6 3.99
7 5.33
8 8.88

I feel confident that these problem builds are isolated, be it through misbehaving components, build issues, etc., and not the fault of the manufacturer. I'll keep offering up what I can to help, however.

[Doc Plus]

My build worked but I noticed I have forgotten to add Z1. I added and tested it, it worked ... and I cutted the excess with the power on (yeah stupid) ...
The bypass always works but when I switch on, it's like a tremolo (the led works). grrrrr

IC3 and C19-C22 are really hot.

IC3
1- 9.3
2- 0
3- 0
4- 0
5- 0
6- 4.5
7- 4.2
8- 9.3

I tried another max1044 (IC3) and I got the same values.
The pin problems are 2, 4 and 5.
All electrolytic caps are 50V except C18 which is only 16V.

[madbean]

Check cap orientation, remelt solder on the pads for IC3 and C-19-C22, and then recheck the voltages and see if you get a different reading this time. You are fine on C18 being 16v.

[Doc Plus]

Check cap orientation, remelt solder on the pads for IC3 and C-19-C22, and then recheck the voltages and see if you get a different reading this time.

I did this and it changes nothing.
Once again, my build worked but I did a stupid thing = cut the excess of Z1 with the power on.

Hot IC3 and caps (C19-C22), what does it mean ?

[madbean]

It's possible the caps got fried. Are the tops bumped out at all...like a little bulge?

They should definitely not be hot. It may require replacement