looking for a pcb audio probe

[copachino]

i have many errors this week, i tried to repair por on SHO(fo-SHO version), chage a bad pot on lavache, and my own layout of the english man stopo working too, and i dont know why, seems everything fine, nothing burned, nothing jumpered, solder are good, and had reflow some just in case, but i get nothing, i hear on the SHO the crackled pot but i cant hear sound, i hear the pop alse but no sound(in fact sounds like ground) so im thinkin on use a audio probe to track my mistakes, or bad componetes, but i have never manage to work something, even the simplest RG keen just a cap con a guitar cable never worked for me...

so does anybody have a layout of a pcb audio probe willing to share??

[muddyfox]

That's all an audioprobe is. A cap stuck to the tip of the guitar cable. No schematic, no pcb.

All you need (and that's how I was doing it in the beginning) is a guitar cable, two crocodile leads and a 100nF cap (some sort of ceramics). Here's what you do. You plug one end into your amp (any POS amp you might have, if you have a fancy tube amp it's prolly safe to get a little one just for testing) and use one crocodile to connect sleeve of the other end to any ground on your board (jacks/battery/3pdt, wherever) and the second crocodile to connect the tip to one cap leg. The other leg is now officially your audio probe!  See here, I just fashioned one for the photoshoot:



connect the white alligator to any ground in your circuit, hold the cap and use the extended leg to probe around (more on that later).

Before I got Jacobs testing rig, this was my main test rig:



I got a cheap guitar cable and chopped off one end. In it's place I soldered this thing:

http://www.ebay.com/itm/SN9F-1-Set-Multifunction-Digital-Multimeter-Probe-Test-Lead-Cable-Alligator-Clip-/400610230032?pt=AU_B_I_Electrical_Test_Equipment&hash=item5d463aff10

It costs next to nothing and I used only one alligator (black for ground) and one probe (red for probing around):



As long as the cable was cut, I soldered the cap directly to the cable (red/tip wire):



Now, you can use any ceramic cap. Greenie like in the picture, box, disc.... this one in the picture isn't even 100nF, it's 82 and it works just fine. 47 would work as well, it's really just a DC blocking cap so that you don't blow out your amp/speaker with a possible DC spike.

How do you use it? Just grab the circuit schematic, follow the signal path and touch various points on your board. If everything is all right you should hear your guitar signal through your amp. So probe places like pcb input/output, ic opamp outputs, that sort of thing. If you probe ground you'll get silence, if you probe power you'll get hum.

So... any questions? 

[rullywowr]

Excellent writeup and pictorial, Muddy!

[wgc]

Worth it's weight in gold.  I did something a little different by soldering to a jack instead of chopping a cable. Great write up!

[davent]

As they say a pictures worth a thousand words and the first picture up there kills it... perfect!

[copachino]

That's all an audioprobe is. A cap stuck to the tip of the guitar cable. No schematic, no pcb.

All you need (and that's how I was doing it in the beginning) is a guitar cable, two crocodile leads and a 100nF cap (some sort of ceramics). Here's what you do. You plug one end into your amp (any POS amp you might have, if you have a fancy tube amp it's prolly safe to get a little one just for testing) and use one crocodile to connect sleeve of the other end to any ground on your board (jacks/battery/3pdt, wherever) and the second crocodile to connect the tip to one cap leg. The other leg is now officially your audio probe!  See here, I just fashioned one for the photoshoot:



connect the white alligator to any ground in your circuit, hold the cap and use the extended leg to probe around (more on that later).

Before I got Jacobs testing rig, this was my main test rig:



I got a cheap guitar cable and chopped off one end. In it's place I soldered this thing:

http://www.ebay.com/itm/SN9F-1-Set-Multifunction-Digital-Multimeter-Probe-Test-Lead-Cable-Alligator-Clip-/400610230032?pt=AU_B_I_Electrical_Test_Equipment&hash=item5d463aff10

It costs next to nothing and I used only one alligator (black for ground) and one probe (red for probing around):



As long as the cable was cut, I soldered the cap directly to the cable (red/tip wire):



Now, you can use any ceramic cap. Greenie like in the picture, box, disc.... this one in the picture isn't even 100nF, it's 82 and it works just fine. 47 would work as well, it's really just a DC blocking cap so that you don't blow out your amp/speaker with a possible DC spike.

How do you use it? Just grab the circuit schematic, follow the signal path and touch various points on your board. If everything is all right you should hear your guitar signal through your amp. So probe places like pcb input/output, ic opamp outputs, that sort of thing. If you probe ground you'll get silence, if you probe power you'll get hum.

So... any questions? 

i just tried it and im about to leave... i get it work on bypass by putting probe to input jack and works fine, when i engaged the effect, i got nothing, even if i put right on the output tip... i get no sound at all, i can hear the pot crackle, i can even hear if i touch the tip on the input jack, but i get no sound at all, all i hear its a buzz, not like the ground sound but a buzz

[davent]

The boards grounding your input?

[copachino]

The boards grounding your input?

rings are grounded, but i get no sound,  in bypass i get fine, but on fx got a buzz... i just chaged a pot and got nothing since then... have rechange pot but the pot its fine

[copachino]

maybe i have burned the transistor when i change the por, since the fo-SHO its a very small board i get hot like hell even when you are soldering other pats, everything gets hot... i will try to change the tranny tonite... maybe those are my problems

[davent]

When you have the switch set for bypass you get the guitar signal at the input jack, do you get the guitar signal at the output jack?

Do you have any clear, closeup photos you can show us?

[copachino]

When you have the switch set for bypass you get the guitar signal at the input jack, do you get the guitar signal at the output jack?

Do you have any clear, closeup photos you can show us?

the bypass works fine, maybe tonite will post some photos, i dont have the pedal at my work... but.. i have tested voltages, and the are normal, but the tranny have 9v, 9v,9v on each pin (ground reference) so maybe i think i have blow the tranny resoldering the board

[mgwhit]

Update: Just read your post where you have 9V on each pin of Q1.  Swap that puppy out!

--

Have you actually used the probe on the circuit board yet?  The entire point is to trace where in the circuit you're losing the signal.  Try these points in order:

1. the IN pad of the board -- if you don't have signal there it's a problem in your switch wiring.

2. the gate of Q1  -- if no signal you either have a bad solder joint or (unlikely) a bad cap at C1.

3. the drain of Q1 -- (make sure your boost is set to about 9-11 o'clock) if no signal you either have a bad solder joint, a bad pot or a bad MOSFET at Q1.

4. the OUT pad of the board -- if no signal you either have a bad solder joint or a bad cap at C2.

Good luck!

[davent]

If the signal's lost at the inpad when the fx is engaged could also be a solder bridge short to ground there, if there's a pulldown resisitor- a very small tiny value mistakenly used instead of the big Mohm value usually used would in effect, short to ground.

[muddyfox]

Yeah, you really need to pinpoint the exact point where the signal gets lost. The four points above should get you there.

[davent]

Opened my 2 in 1 (2 SHO's) and the  BS170's read;  D/G/S- 6.17v/2.4v/1v and 5.63v/2.4v/0.55v. No idea what they are suppose to be but the pedal works great so no reason to suspect otherwise.

If you're pulling the bs170 you might want to install a socket for the next transistor until you get things sorted.