More low rider problems (updated per tech help rules)

[midwayfair]

Just realized I didn't include this when I moved the more recent problem to a new thread ....

(1) Project Name
Low Rider

(2) General description of the problem
Extremely low output, despite having worked correctly when plugged into the testing rig prior to boxing. Now it does not work in or out of the box.

It also seems to drain the battery much faster that it should.

(3) Steps that you have taken to try to resolve the issue
Described more extensively below. I have inspected the values of all parts several times (despite not having changed anything since it worked on the test rig) and reflowed solder at all the off-board points. I removed the LED to reduce the parts that could have gone wrong. I have tried both a battery and power supply and the problem remains. I have checked with the multimeter for blown diodes. I have used an audio probe and I am able to get signal on some random places like, say, pin 8 of IC 6 (iirc), but not at the clean volume pot and not at the board's out pad. I have checked every part for proper continuity to the next part in the circuit. I am getting voltage to the chips (provided below), although I don't know what's correct. I have replaced all the ICs.

(4) List any substitutions you used for parts/values
Per the build doc, lowered the value of C10 and omited C12 to increase the upper octave.




This board worked perfectly fine the last time I plugged it into the breadboard. I had had an issue previously where there was a broken diode, which I found the following day. After fixing that, it worked just fine. I plugged it into my testing rig as recent as last weekend.

Today I finally got the enclosure drilled and painted, I boxed it up and ... thbt. Dead.

There IS some sound. It's very, very faint and very distorted. There is a little white noise that changes when I turn the clean pot. Bypass works fine.

I've replaced all the ICs. I've checked for continuity on all ground points. I unboxed the thing except for the power jack (to avoid desoldering it) and it still doesn't work. I've reflowed the input/output and power wires. My multimeter says that the switch is working the way it's supposed to.

I'm getting voltage on all ICs, though I'm not sure if I'm getting correct voltages.

At this point, I can't think what can possibly have changed from boxing it up.

[alanp]

Have you got black tape on that pot in the foreground (DOct1, I think)? The board isn't shorting on the chassis at all? (It's a fair size.)

[midwayfair]

Have you got black tape on that pot in the foreground (DOct1, I think)? The board isn't shorting on the chassis at all? (It's a fair size.)

I took it off the pot to examine the lugs. But the board doesn't work OUTSIDE the box anymore, either. I guess my next step is removing it from the harness entirely, but I really hate desoldering switches.

[midwayfair]

Some additional weirdness: When I plug and unplug in the battery or power supply, there's a weird sound, like a woosh and a chirping. It's also eating my battery, but not enough to get the battery hot.

So this leads me to believe there's a problem in the 9v path, but I can't fathom where.

[stecykmi]

pull all the ICs and check the voltages at the supply rails. then start plugging IC's in 1 at a time and checking supply rails again.

[midwayfair]

Some updates. New questions in bold.

I checked the ICs. Nothing jumped out at me on my measurements, i.e., no 0s on the supply rails or anything like that, but I'm way less familiar ICs and I can't go much deeper. I'm going by memory, I'll get some exactsies later.

I've gone over the board once more. Still no broken parts found.

I also got out the audio probe: I'm getting proper signal at Pin 1 of IC6, which is fairly late in the audio path for the upper octage, but the wiper of the clean knob is the same extremely faint sound. That's as far as I got last night.

Since the clean signal depends on regulated 9v voltage and it looks like Pin1 of IC6 might be getting full voltage, should I start looking at all the +9v Reg supply lines?

Would I still be getting sound at all if I had blown the regulator way back when I had some ICs flipped? It doesn't explain why it broke after working fine, but maybe I did something I don't remember.

How do I test if the a regulator is broken?

There are just so many test points. Back when it was working, I thought, "Why iz this genius? Me no genius and it work!"

[midwayfair]

Voltages

Without chips (with chips in parens)
Battery: 9.15

IC 1 (pins 1-8):
1: 4.96
2: 4.96
3: 4.53
4: 0
5: 9.13
6: 0
7: 0
8: 4.64

IC 2 [this looks weird ....]
1: starts at ~2 and then drains
2: drains
3: drains
4: 9.11 [my battery drained a little]
5: 0
6: 4.56
7: 4.43

8: 0
9: 4.5
10: 0
11: 0
12: drains (started at about .5)
13: 0
14: 0

(With chip in: 1, 2, 3, 5, 6, 7, 9, 10, 12, 13= 4.76, 4 = ~9; 8 = 0, )

IC 3
1--6: all 7

8:
(2: ~9, 4: 7.6)
(8, 10, 11, 14 = ~9)

IC 4:
(with chips: 2, 5, and 9 = ~9, all others = 0)

IC 5 & 6
(With chips: 1, 2, 3, 5, 6, 7, 8, 9, 10, 12, 13, and 14 = 4.85)
(4 = ~9 and 11 = 0)

[midwayfair]

Bump for help and updated first post per tech help rules.

Are there any parts I should just replace because they might have blown and I just won't know it?

[oldhousescott]

I'd be tempted to start by removing all chips except IC1 and IC6, and removing all pot wiring except the clean pot and see if you can at least get clean signal passing through. After that, I'd reconnect the up octave pot wiring and see if you can get that going. Last, tackle the down octave stuff.

Your pin numbering looks suspect as well. Remember, as viewed from the top, they count in a CCW direction, starting with pin 1.

[midwayfair]

Still no clean sound with just the clean circuit stuff in.

Should I start replacing "blowable" parts at this point? The only reason I can think of that a board would stop working is that something polarized has blow up and is sending the signal to ground early. And the only polarized components I can't measure are capacitors.

There's only three polarized components I can see in the clean path -- the J201 and two electrolytics. C4 seems like the most likely candidate to my eye -- if it blew and was conducting, it would send almost the entire audio path right to ground before it ever went through an op amp. It would also connect part of VR to ground, which might explain why the battery is draining even though the chips are getting voltage. I don't really have a way to test capacitors, and nothing smells or looks broken, but I really can't think of anything else that would just outright kill the sound on a working board that hasn't changed.

Does anyone else have any ideas of what else could be dead wrong before I start desoldering components in a haphazard fashion?

[jkokura]

Because the battery is draining quickly I would suspect your power is leaking to ground somewhere. Does the battery heat up as well?

Jacob

[midwayfair]

Because the battery is draining quickly I would suspect your power is leaking to ground somewhere. Does the battery heat up as well?

Jacob

The battery doesn't heat up, but there was a ~.2v drop from the battery even in the space of time (20 minutes?) I was measuring voltages, without any input. I'm fairly certain that this effect without an LED shouldn't have used battery life that quickly.