Mach 1 no sound when engaged

[ADAOCE]

Have a Mach 1 that has no sound at all when engaged. Bypass and LED work fine. I’ve checked my solder joints. Didn’t see any cold looking joints. I touched up a few resistors so that the solder penetrated both sides. I even tried a different opa2134 and a tl072.

I’ve recorded the following IC voltages with the opa2134

1: 4.46
2: 5.03
3: 0
4: 0
5: 0.16
6: 0.59
7: 4.46
8: 8.2

I’ve attached some pictures of the board from the top side. I know it could use an IPA wipe down but to be honest that’s never resulted in an issue like this for me and I’ve done ones that looked worse.

mill have to wait til tomorrow to get a picture of the underside (I stupidly didn’t take a picture when I pulled it out to reflow joints). Underside looks better than top though since that’s the side I soldered from.

anyways I’m just hoping these ic voltages are enlightening. TIA

 

[ADAOCE]

Just touch the iron to it until it melts and flows nicely.

Ok so reflow these joints then clean board and test voltages again? Then keep going down your list of tests? Unfortunately I don’t have another 22u cap if that is bad. Would a 47u or 10u be sufficient. I could always just deal with noise until I get a 22u

 

[Chas Grant]

Unfortunately I don’t have another 22u cap if that is bad. Would a 47u or 10u be sufficient. I could always just deal with noise until I get a 22u

Should be able to. the 10u should work, you may hear a little more noise or "hum". The 47u should work also, but never seen the first cap smaller than second cap. Normally I see like 100u and 47u. My gut says a 47 should work, but then my gut could be hitting the crack pipe right now!

 

[ADAOCE]

Ok I’ll try all this and report back. Thanks guys

 

[Chuck D. Bones]

For both C100 and C101, more capacitance is better, within the physical constraints of fitting them in the box. Use what you have, but don't go changing parts unless you know they are bad. Otherwise, you'll end up damaging the board swapping out parts that don't need to be swapped out.

Those photos aren't too helpful; most of the solder joints are out of focus. You get better pix when the board and focal plane are nearly parallel.

 

[ADAOCE]

You get better pix when the board and focal plane are nearly parallel.

Ok thank you. I’ll take better pics when I open it back up tonight

 

[ADAOCE]

form new plan of attack..

Unfortunately this is where we are at now. I reflowed the suspected components and got rid of any cold looking joints and really cleaned up the board as best I could (tough with the pots on the board). No change for any of this. I took out C101 and still no change.

Here are some pictures from after all of this.

 

[ADAOCE]

Higher quality

 

[Chas Grant]

DARN IT!!! Thank You for pulling that cap though! Based on the info you provided C101 was high on my list. Here was the reasoning. On R101 8.2V on top but .47V on bottom, this is your main issue, could be caused by short to ground anywhere in Vref path, open on R101(resistor or cold solder joint), leaky cap(C101 due to how low voltage is) or something loading down voltage divider hard. But you stated that both R101 and R102 read 4.2K, in my book both of those are good, there can be parallel paths in the circuit that lower the resistance of the voltage divider network, Since this is designed with an OPA2134 then they most likely took the time to account for this and the 4.7K and 5.6K both are 4.2K in completed circuit which will put Vref at half of Vcc. This to me is good engineering. Now if the 4.2K on those 2 resistors is accurate, then a cold solder joint on R101 or short around R102 is low on the list, either one of these would drastically change the resistance. It doesn't mean that's not the problem, just lowers them down the list. Now when you pulled the IC from the socket, you removed the most obvious parallel paths and reduced the possible paths for a short. I don't know the internal resistance\impedance of the power supply stage or the output stage of the op amp, so get it out of the equation. It should be high, but but not to high, but I have seen it lower than what I expected on some op amps. With the op amp removed, still no Vref on it at any pin, so this points back to voltage divider. The one component you can't check in the voltage divider circuit is C101, and it keeps popping up as a suspect, that is why I asked it to be removed. Just rename that cap Keyser Soze`!

OK enough of that, I could keep going but you still have a non functioning pedal, and this is a humdinger of an issue. I normally like to troubleshoot with voltages, it's just how I learned and it is easier on the small PCB cause you can clip the black lead to ground and just worry about read lead. But I want check continuity. So if you could take the following real quick.
R101( the side you had 8.2V on) to pin 3 of ic socket (to be safe make sure no ic in socket)). Should be 434.7K
Same spot on R101 to pin6 of IC socket, Should be 433.9K

The next 3 should have a very high or open resistance
R101 to R11 Open
R101 to R12 Open
R101 to pin3 of tone pot.
Please post findings when ever you can. If the radings are low you can try to isolate it y using schematic

 

[ADAOCE]

.
R101( the side you had 8.2V on) to pin 3 of ic socket (to be safe make sure no ic in socket)). Should be 434.7K
Same spot on R101 to pin6 of IC socket, Should be 433.9K

The next 3 should have a very high or open resistance
R101 to R11 Open
R101 to R12 Open
R101 to pin3 of tone pot.
Please post findings when ever you can. If the radings are low you can try to isolate it y using schematic

Ok so R101 to IC3 is 431k
R101 to IC6 is 8.5k

Open on all three (R101 to R11, R12 and pin3 tone)

 

[Chas Grant]

Crap, R101 to IC 6 should be about 9.5K so 8.5 is OK, my bad higher math kicked my butt. So all these look good. Everything is pointing back to voltage divider, try to measure resistance across R101 and R102. You should be able to get this from backside +9 and ground pads

 

[ADAOCE]

Crap, R101 to IC 6 should be about 9.5K so 8.5 is OK, my bad higher math kicked my butt. So all these look good. Everything is pointing back to voltage divider, try to measure resistance across R101 and R102. You should be able to get this from backside +9 and ground pads

Ok so the original number for R101 to IC6 of 433.9k was wrong? Damn I was hoping we found our issue!

By resistance across R101 and R102 do you mean measure the resistance on the + and - side of the voltage divider itself? That’s how I’m understanding it since the divider has ground and Vcc on either side.

 

[Chas Grant]

Ok so the original number for R101 to IC6 of 433.9k was wrong? Damn I was hoping we found our issue!

By resistance across R101 and R102 do you mean measure the resistance on the + and - side of the voltage divider itself? That’s how I’m understanding it since the divider has ground and Vcc on either side.

Yes!! It’s the easiest way to measure the resistors and it also checks continuity through that part of the circuit

 

[Chas Grant]

One other thing, when taking the measurement, red lead to 9v and black to ground pad, this way you forward bias the diode

 

[ADAOCE]

Yes!! It’s the easiest way to measure the resistors and it also checks continuity through that part of the circuit

I get 4.67k across R101 and 5.56k across R102 and 10.25 with a leads on the inner sides of R101 and R102

 

[ADAOCE]

One other thing, when taking the measurement, red lead to 9v and black to ground pad, this way you forward bias the diode

If input the leads on these two points I get about 19k for a moment then OL

 

[ADAOCE]

FWIW I get 3.87k between IC6 and the divider (after R101 and R102) but nothing between the same point and IC3

 

[Chas Grant]

If input the leads on these two points I get about 19k for a moment then OL

That’s not what I was expecting! But it could mean we are close. Recheck the last measurement 9V pad and ground pad. If you check it and it goes right to OL that’s ok. It may, if C100 can’t discharge.

 

[ADAOCE]

That’s not what I was expecting! But it could mean we are close. Recheck the last measurement 9V pad and ground pad. If you check it and it goes right to OL that’s ok. It may, if C100 can’t discharge.

19.9k then right to OL and then did it again and got 15.5k then right to OL

 

[Chas Grant]

Alrighty then, you may have an open in power supply section. When you measured from the voltage divider to pin 3 and pin 6 of the ic which resistor did you measure from?

 

[ADAOCE]

Alrighty then, you may have an open in power supply section. When you measured from the voltage divider to pin 3 and pin 6 of the ic which resistor did you measure from?

Ah dunce cap my meter is not auto ranging I get 427k from either R101 or R102 to IC3