Output/sound issues on a Boiling Point build

[Ambugaton]

First off thanks for all the input guys. I really appreciate it. I know the problem will be solved by going over my work and I know it probably is frustrating at times, but nonetheless you are still helping me. Thanks,

I quickly checked Q2 this morning and there is in fact a short between C and B. I also spotted a bridge that I previously missed but didn't have time to fix it and remeasure.

I knew the IC was 1-4 on the left side but did not realize that the right side would be 8-5 from top to bottom? Hahaha. Man, glad I know that now.

I will see if i can get another MPSA18 transistor locally and figure this out and really inspect the Vero again. Thanks again for the patience.

[Ambugaton]

your R12 appears to be not 510k - any other subs we should know about?

Yes and my bad for not mentioning, I did use slightly different R values (based off of what I had on hand) for the following:

4M99 ---> 4M7
620K ---> 680K
510K ---> 470K

I didn't think this would make a huge difference since the +/- 5% tolerance has some overlap between the values I used.

[Ambugaton]

Being that I am a visual learner I made a path of the signal to test with the audio probe. I imagine the signal probably runs into problems at Q2. I guess it would probably help to do a similar visual for the voltage as well but I will start with:

1) Examining the tracks near the strips where the C and B of Q2 to ensure there is no bridge

2) If not, disconnect C and check readings on Q2 again.

I don't know if fixing the issues with Q2 will adjust the voltage readings on the IC but ...hopefully it solves everything.

[GibsonGM]

Once you have removed Q2  (how was Q1, by the way?), I'd power up briefly to see if the IC supply voltage and ground are ok.    You can also check all 3 holes where the Q legs go to make sure they aren't shorted, before installing the new Q's.   (and after, too!)

IC pin pattern.  "Notch" on IC goes at top:
1   8
2   7
3   6
4   5

[Ambugaton]

Once you have removed Q2  (how was Q1, by the way?

Q1 readings seem more in line:
C: 9.3V
B: 2.3V
E: 3.2V

and yeah I have labeled the pins correctly. Still have an issue with 5, 6, and 7 it seems. I should be getting something similar to this:

4.56|----|9.16
4.60|----|4.56
4.47|----|4.56
0.00|----|4.55

My readings:

4.7|----|9.3
4.1|----|7.1
4.0|----|2.9
0.0|----|2.9

I think... holy shit I just confused myself. I thought I corrected the error I made with the pinouts for the signal path picture... but now I am looking at it and it seems like I still labeled P5 - P8 incorrectly. Wtf.

I will correct and reload.

[Ambugaton]

IT'S ALIVE!!!!

So I found a bridge that was shorting out Q2. Fixed that and doubled over any other potential issues with a magnifying glass...

Thought I fixed it there but it still had no output... So out of frustration i fidget with each pot and realize that when the tone pot was around 50% I had signal going through!!! I think I just have a faulty tone pot... as I turn it down from 50% it gets scratchy and ugly and then bammm nothing. Same going up to 100%.

Thanks again for everyone's help. My final voltage readings in case there are other issues:

IC:
P1: 3.68V
P2: 4.22V
P3: 3.78V
P4: 0.00V
P5: 2.20V
P6: 2.20V
P7: 4.65V
P8: 9.34V

Q1:
C: 9.34V
B: 2.20V
E: 2.99V

Q2:
C: 9.34V
B: 2.53V
E: 3.07V

Does all of that jive? I feel like Pin 5 & 6 are a little wonky compared to other readings I have seen on the web (Can't find one specific to the Boiling Point though)

[Slowpoke101]

It is good to see that you are getting this thing sorted. Just a few things that would be a good idea to check.
The voltages on the chip are getting closer to what would be expected but pins 5,6 and 7 are still not good. The way that you describe how the tone pot is currently working leads me to suspect that the pot's wiper (centre pin going to the Tone2 board connection) is shorted to 0V or close to it. This could be that C6 (0.15uF) is crook or that you have another tiny piece of copper or solder along the vero trace going to the Tone2 connection. Have a look and see.

Cheers.

[Ambugaton]

Well damn... one step forward 2 steps back I guess.

I inspected for any additional bridges (Used a flashlight on the component side and inspected the copper side... made it really obvious if there was anything even close to a bridge...)

Now I am getting 9+ volts on each IC pin and Q1 & Q2 are all way high as well. In the ballpark of 6V - 8V on B and E of each transistor.

I'm so lost now.

The audio probe shows everything working fine up to Pin 3 of the IC. I get no signal at Pin 1 now.

[Slowpoke101]

The fun of troubleshooting. It isn't really that much fun.
If pin 4 of the IC is reading 9V you have lost the 0V (ground connection). Depending on where you are connecting the multimeter's negative lead can cause confusion. If the meter is connected directly to the battery (or power supply) negative and the board's ground becomes disconnected, you will read 9V everywhere. Check your wiring.

Cheers.

[Ambugaton]

Pin 4 is still 0V. Should have stated that. The worst part about this is that I did have it working despite some problems with the tone pot and it sounded so incredible. Maybe I botched a connection while messing with the board and clearing shorts.

[Slowpoke101]

A botched connection is most likely. I suggest that you check the voltage across the 47uF capacitor (C11). This capacitor should have about 4.5V across it. R16 and R17 make up a resistive voltage divider that supplies the 4.5Volts (shown on the circuit as VR). This voltage line is critical to the circuit's operation. Check that R17 is still connected to ground.

[Ambugaton]

I think I found it... I have R17 (I believe) connected to the wrong strip... It is not connected to ground.

[Ambugaton]

Dude I can't thank you all enough. Slowpoke thanks for sticking it out. That fixed it and everything works perfectly. It was hinted at being a problem with R16 or R17 from the get go. Learning experience and appreciate everything!

[Slowpoke101]

Very pleased that you have got it to work. I'm sure that everyone else is too. Enjoy your new effect and keep building.

Cheers.

[GibsonGM]

Awesome, Ambugaton! 

Remember: you can take voltage readings as you have been, and then remove power and use the continuity setting (beeper) to see if 2 places are connected.  That works GREAT for seeing if a place is going to ground!  Or to see if IC pins are shorted (remove IC, you can check to see if they are 'connected' and should not be) etc       

Just make sure to remove battery first.

[duck_arse]

excellent work, Ambugaton, but it's not over yet. you MUST now measure your voltages again, and post here for all to see. your transistors should have around V+/2 on the base (4V5), and, being darlingtons, the emitters should be two diode drops lower, so about 3V3.

[ edit :] blast! these mpsa's confuse me.

[Ambugaton]

Final Readings:

IC
4.42|----|9.36
4.82|----|4.45
4.50|----|4.45
0.00|----|4.45

Q1
C: 9.36
B: 2.54
E: 3.69

Q2
C: 9.36
B: 3.02
E: 3.77

A little confused on what the Q's should be

[thermionix]

being darlingtons

Nope.  MPSA13 is darlington.  MPSA18 is not.

[duck_arse]

thanks therm. I coulda sworn I looked those up. but still, I think your base voltages are off. the emitter voltage should be, being a non-darlington, silicon, npn bipolar transistor, one diode drop lower than the base. I'm fairly sure this holds even for the emitter follower configuration.

[Ambugaton]

So you are saying that the emitter on both MPSA18's should be about 0.7V lower than the base? I thought I read something that said the base should be lower than the emitter...?

What readings would be considered "within range" in this circuit? I found someone else's readings from this build and it was pretty close to what I have at the moment.