Are ALL my diodes bad?

[brucer]

Hi All.

I've populated one of Rullywow's "DC-R Comp" (DynaComp version) PCB's (http://www.madbeanpedals.com/forum/index.php?topic=17134.msg163123#msg163123)), but I'm getting zero sound when I try to rock before boxing. 

Using an audio probe, I get a signal as far as pin 2 of Q1 (2N5088), but I get no signal on pins 1 or 3.  I've swapped in 5 different diodes, but still nothing.

Is it possible that I've got 5 bad diodes or should I be looking somewhere else for the problem.

Any and all help appreciated.

Thanks, Bruce.

[TGP39]

Hi Bruce. Are you putting the transistor in the correct way?  I would like to see some voltages on Q1.

Steve.

[TGP39]

A few basic questions/requests.
1. Do you get guitar signal in bypass mode?
2. I'm sure you already know, but when you look at the face of the 2N5088 transistor the legs from left to right are E/B/C.
3. This build is a bit tricky because of the changes between the Ross circuit and the Dynacomp. This makes posting a picture of your board a must.

We'll get this thing working. 

Steve

[brucer]

Hi Bruce. Are you putting the transistor in the correct way?  I would like to see some voltages on Q1.

Steve.

Thanks for responding so quickly!  Love this place.  The voltages I'm seeing on Q1 are:

- Pin 1: zero v
- Pin 2: zero v
- Pin 3: -9.25 v

Do they make sense (the absence of voltage at Pin 2 is troubling to me ... but that's with zero knowledge of how these things actually work!  )?  I did try rotating Q1 180 degrees, but then just got white noise on Pin 2 and still silence on Pins 1 and 3 ...

On the other points:

1. There is no bypass mode with my testing rig, but I get guitar sound on the components before Q1
2. I did check the pinouts online and on the schematic and I think (pretty  sure, mostly) I've got it inserted correctly
3. Always a little humbling to post pictures, but here it is!

[jimilee]

Well there's the problem, you're missing transistors......but seriously, Did you turn the bias all the way down? Also, reflow, and check you have no bridges. It's hard to tell from the photo.


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[jkokura]

Your soldering seems like it could be the issue. If you look closely, you'll see that two of your pins on Q1 seem to be soldered together. If you clean up your soldering there, and elsewhere, it may just start working for you.

Jacob

[TGP39]

Your soldering seems like it could be the issue. If you look closely, you'll see that two of your pins on Q1 seem to be soldered together. If you clean up your soldering there, and elsewhere, it may just start working for you.

Jacob

+1. I agree with Jacob. Your Q1 voltage readings convey a shunt. Most definitely due to solder bridge. Separate that solder bridge and use your continuity tester to make sure they are indeed not attached anymore.

Steve.

[wgc]

Don't know the circuit or the mod, but also check that any missing components don't need a jumper instead.

[Govmnt_Lacky]

Your soldering seems like it could be the issue. If you look closely, you'll see that two of your pins on Q1 seem to be soldered together. If you clean up your soldering there, and elsewhere, it may just start working for you.

Jacob

Actually... Q1 pins are partially obscured by the Sustain pot in your pic.

I believe the pins that are shorted are between C6 and R5 which look to be shorted anyways according to the schematic.

Your C4 pins look to be possibly shorted together though... check all of your solder points and ensure continuity with a DMM according to the schematic 

[brucer]

Thanks guys.  I sincerely appreciate it.  Unfortunately, I'd checked for solder bridges before posting (and checked anything that looked like it might be a solder bridge against the schematic to see with it would cause an issue (thinking that a solder bridge between two ground connections wouldn't cause an issue, but maybe I was wrong ... or missed something)).  Anyway, always good to check again, so I re-flowed all solder points and re-examined for solder bridges with a magifying glass, but there's still no guitar through the audio probe past the centre pin of Q1.  I'm currently checking for circuit continuity with my multimeter in reference to the schematic. 

[TGP39]

Bruce....how are you jumpering R4, R6 and R9?  I don't see any jumper in those spots or am I missing something?

Steve.

[brucer]

Good question.  The PCB has mini solder pads between where you'd put the leads of the omitted part.  A dab of solder spans the mini pads and forms the jumper. 

[blearyeyes]

"mini pads" might be "vias" which move the trace from one side of the board to the other. Shouldn't be soldered.
But I don't know what you are working on.

Carry on!

P.S. never had a bad diode.  Put them in backwards a bunch of times!