But wait, there's more ... Lowrider problems

[midwayfair]

This is a book that follows. Sorry about the lengthy post, but I've been extremely thorough in my troubleshooting ...

Previous tech help thread for reference:
http://www.madbeanpedals.com/forum/index.php?topic=4888.0

(1) Project Name
Low Rider

(2) General description of the problem
Extremely low output. (The output is so low that if I boost it with the loudest pedal I own, it can get to unity.) Sometimes functions properly before boxing.

(3) Steps that you have taken to try to resolve the issue
Extensive history: This worked once a long time ago after I discovered a broken diode. Then I put it aside while I waited to finish the box. Tested it again before it went in the box and it worked exactly like it's supposed to. Boxed it once -- dead. Removed it from the box -- still dead. Troubleshooted it for weeks and couldn't find a problem.

Recent steps taken to resolve the issue:
-It was suggested that my problem was a grounding issue, so I reflowed all the solder joints to ground and all socket solder joints.

-Replaced all ICs.

-Replaced the in/out wires and the power wires, reflowed solder on the pots.

-Replaced all the polarized caps.

-Replaced the J201 with a socket in case it had blown.

-Replaced D7. No improvement. LIFTED D7.

-Scraped between the power pads to make sure there wasn't a solder bridge.

Then, last night, I just started poking at the pins of IC1 with one my multimeter's probes, and all of a sudden it started working. I wiggled the chip and it didn't stop working. I wiggled all the wires and pots and it didn't stop working. I shook it a bit and it didn't stop working.

I was a little frustrated that I couldn't figure out what had been wrong, but I wasn't about to argue. So I wired up the harness again and soldered the board into the switch.... and it was back to the extremely low output problem.

-I probed a little and the power line was getting continuity to ground sometimes in some really strange places. I got a beep intermittently at the +9v in and ground, but sometimes only (I think) when I had the black probe on the +9v.

-I got continuity on either side of D7 with the same orientation. I lifted D7 again and got .99 resistance on either side of the pad but no improvement in sound.

-I got continuity to ground on the ANODE side of the LED. This makes NO sense to me, because the LED is working fine and there's a 2.7K resistor on the other side of it. I haven't removed the LED yet, just in case the 2.7K resistor is somehow draining power (it's a smaller resistor than what's on the +9v in the schematic), but I've never heard of that problem before and only just now thought it might be a possibility.

Although I realize that an intermittent problem like this is usually a bad solder joint, that simply doesn't make sense in this instance. All pins of IC have continuity to the right places and it's seated securely in its socket.

I'm convinced that the problem is somehow centered around IC1 and the power section, but the multimeter and my eyes tell me nothing is wrong.

(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.

-Finally, I'm using a snap-in DC plug (two lugs) with tape isolating the lugs, enclosed jacks, tape on the back of the pots , and all fresh in/out wires, and bypass and the LED work. I'm fairly certain that the box itself is not a problem.

[madbean]

First off, this is a model of how to start a tech help thread. Very detailed! And, you've obviously put in a lot of work to try and resolve it.

The first quick thought I have is: you did not mention the actual 3PDT. Any chance that could be the source of the problem? You got it working out of the harness. Then re-installed and your volume is bleeding off. One possibility is the input or output is bleeding somewhere on the switch.

Try this: disconnect the input/output wires on the jacks. Tack solder the input and output wires from the PCB to them to create a temporary 'no bypass'. See if you still have the same problem plugging straight through. If not, then your 3PDT is the culprit.

One other thought: you big blue cap there is sticking up past the top to the enclosure. Any chance when you flip it over, it is creating downward pressure on the PCB, and forcing a contact between the bottom of the PCB and the pot casings?

[midwayfair]

First off, this is a model of how to start a tech help thread. Very detailed! And, you've obviously put in a lot of work to try and resolve it.

The first quick thought I have is: you did not mention the actual 3PDT. Any chance that could be the source of the problem? You got it working out of the harness. Then re-installed and your volume is bleeding off. One possibility is the input or output is bleeding somewhere on the switch.

Try this: disconnect the input/output wires on the jacks. Tack solder the input and output wires from the PCB to them to create a temporary 'no bypass'. See if you still have the same problem plugging straight through. If not, then your 3PDT is the culprit.

One other thought: you big blue cap there is sticking up past the top to the enclosure. Any chance when you flip it over, it is creating downward pressure on the PCB, and forcing a contact between the bottom of the PCB and the pot casings?

Brian, thanks so much for the reply.

The 3PDT switch from this time around is a brand new switch from a different source (this time it's from Tayda, last time I boxed this board, it was from PPP) - I did not reuse the same harness from the last time the pedal died. I'm not saying I did this because I thought of the switch being an issue -- it's simply that I had already reused the other switch from the first boxing in another build (where it worked).

I have not yet put the back on the case, and the board is just sort of floating in the case, so I don't think downward pressure is a problem here yet. I agree that the mojo cap could be an issue in the future, but I'm not sure I can get it back out of the PCB ...

I'll be removing the board from the harness again tonight (after a brief pit stop of removing just the LED first) and I will see if it works on the breadboard again. I would have removed it from the box for further testing before starting another tech help thread, but I snapped this picture literally a minute before I was leaving for work.

[midwayfair]

oh ... if anyone has the right voltages for IC1, IC6, and the J201, that would be a big help. I took voltages in my other thread, but I don't think they were useful.

[jkokura]

The "was working, now isn't" thing is what's shaking me. In order for that to happen, something has to give... literally. Something has to have been overloaded, or changed in some respect. Because you've changed all the ICs and transistors though, it makes it hard because those are the first suspects.

What have you found via audio probe?

Jacob

[nzCdog]

Voltages from a working Lowrider

IC1
1. 5V
2. 5V
3. 4.9V
4. 0V
5. 4.5V
6. 4.99V
7. 5V
8. 9.1V

IC6
1. 5V
2. 5V
3. 9.1V
4. 5v
5. 5V
6. 5V
7. 5V
8. 5V
9. 5V
10. 5V
11. 0V
12. 5V
13. 5V
14. 4.86V

Q1
D. 9.1V
S. 5.32V
G. 4.3V

Hope this helps

[midwayfair]

Voltages from a working Lowrider

IC1
1. 5V
2. 5V
3. 4.9V
4. 0V
5. 4.5V
6. 4.99V
7. 5V
8. 9.1V

IC6
1. 5V
2. 5V
3. 9.1V
4. 5v
5. 5V
6. 5V
7. 5V
8. 5V
9. 5V
10. 5V
11. 0V
12. 5V
13. 5V
14. 4.86V

Q1
D. 9.1V
S. 5.32V
G. 4.3V

Hope this helps

You are awesome.

Here are my voltages (no chips in):

Steady 9.4 from one-spot at board input

IC 1:
1: 4.25
2: 4.25
3: 3.86
4: 9.43
5: 3.96
6: 0
7: Drains (if I leave it alone, it starts around 5 and then seeps away)
8: 0 (?!?! I get a continuity beep from the 9v in but no voltage. How is that even possible? It's 9v if I probe from ground to the pin.)

Obviously there's a major problem there.

Some voltages are different with the chip in. Pin 7, for instance, is 8.4 volts with the chip in and does not drain.

IC 2
1: 3.8
2: 3.8
3: 4.25
4: 0
5: 4.25
6: 5
7: 5

8: 3.9
9: 4.1
10: 4.5
11 9.4
12: 4.5
13: 5.1
14: 5

Q1:
D: 0
S: 9.43
G: 3.87

Also weird.

Audio probe:
Pin 1 on IC1: Clear, but quiet signal. Pretty much "normal" clean volume for this effect, I think, maybe a little quieter.

Q1:
Loud clean signal.

Pin 7 on IC6: Loud and distorted signal.

There are so many voltages on mine that are different, I'm not sure where to begin.

[nzCdog]

Keep the thing out of the case for now... use your test rig so you can easily inspect connections and parts.  Get a bamboo chop stick and gently prod things whilst playing guitar through them... this often shows up dry joints which are hard to see with the eye.  Be systematic, include all solder joints where parts meet the board.  Check for stray strands of wire, reflow your wiring connections and double check for bridges.  Looking at C9 (big blue) its very large, perhaps the leads are shorting against the pcb somewhere?

Failing that its time to get the schematic out and look at IC1 to start with.  Go through the schematic systematically, use a pencil to mark where you've checked in the pcb.  Also, double check, are you numbering off the IC pins correctly? eg



If you are then IC1 shows that you have a 9V/Ground mixup somewhere... pin 4 should be grounded and pin 8 at +9V
Pins 6 and 7 should be the same... but they aren't

Looking at Q1, I read mine like this:


Your Drain on Q1 is also reading 0V when it should be 9V... the same fault as IC1

Somehow you've got 9V getting into the source pin...  have you double checked the pinout of your particular model of J201?  Sometimes manufacturers can vary pinouts, God only knows why.  

Start there anyway mate, let us know how you get on

[nzCdog]

Hey just looking at your pic in the earlier thread... check your square 9V pad on the board, its right next to a round ground pad, and that might be the point of short

[midwayfair]

jeeez I'm an idiot. I was holding the probe to the +9v pad instead of the ground pad. Here's a re-read of the voltages. They make a little more sense but clearly IC1 is not getting proper voltage. These are re-reads with the probe just clipped to the jacks:

9.1v at input (separate power supply instead of the one-spot).

IC 1

IC1
1. 1.16
2. 1.16
3. 4.37
4. 0
5. 1.09
6. .62
7. .62
8. 9.24

IC6
1. 4.81
2. 4.81
3. 4.81
4. 9.24
5. 4.81
6. 3.28
7. 6.33
8. 4.81
9. 4.81
10. 4.81
11. 0
12. 4.81
13. 4.81
14. 5.1

Q1
D. 9.24
S. 5.24
G. 4.37

This makes more sense with what the audio probe gave me.

I went through testing continuity while the power was plugged in, and I got a couple odd things. At first, everything is pretty normal. However, after it's been plugged in for a little bit, I get continuity (sometimes momentary) to the +9v pad at weird places: both sides of D1 (even though the diode tester says the diode is still working right), pins 10-12 of IC6, and sometimes to ground. Basically, at some point, I'm getting continuity between the 9v in and the reference voltage points, even though there should be 10K of resistance. :-/

Of course, after prodding it, when I plugged it in ... now it's a white noise generator and possibly a radio (I think I was picking up some Morse code!). The clean volume actually functions now. Not for guitar input, but you know ...

I ordered another board from Brian. I'm going to rebuild from scratch and use a working model to provide a point-by-point testing of voltage and resistance. At this point, that's probably the only way I can track down the problem, unless of course it's actually something broken inside the board itself.

Thanks for the help and the suggestions, guys.

[PimpMyTone]

I know it s and old topic but I`m building the low rider right now so I`m reading some posts about it ...

Did you put russian germanium diodes for d8-d9 ? They look like D9B . In some russian Ge diodes,  the color stripes indicates the anode and not the cathode . Wel,l if I`m right I think your d8-d9 are backward .

[midwayfair]

I know it s and old topic but I`m building the low rider right now so I`m reading some posts about it ...

Did you put russian germanium diodes for d8-d9 ? They look like D9B . In some russian Ge diodes,  the color stripes indicates the anode and not the cathode . Wel,l if I`m right I think your d8-d9 are backward .

They're smallbear Generic diodes, probably 1N2xx. I'll double check them, but I'd more or less given this board up for dead.

[mercury6]

i know this is a little old but I BUILT 3 OF THESE. got mad and destroyed one but they all 3 had the same exact problem u described and im pretty sure i change almost every ic and transistor on these  lowriders, and touched up solder joints. harrdly any sound at all. a very faint octaver sound if i cranked my amp up really high

[Matt]

i know this is a little old but I BUILT 3 OF THESE. got mad and destroyed one but they all 3 had the same exact problem u described and im pretty sure i change almost every ic and transistor on these  lowriders, and touched up solder joints. harrdly any sound at all. a very faint octaver sound if i cranked my amp up really high

Honestly it would be best to start a new thread with pictures of your builds