Matchbox debug help, please

[tcr77]

Got this kit: http://www.olcircuits.com/olc_matchbox.html

Wired everything up, and here's where I'm at:
1. No signal passes thru box, although there is a definite change in noise signature when I step on the switch.
2. LED only lights up on DC power, not with battery (battery is good, I checked)
3. LED will only light up when a cable is plugged into the output jack. It won't light up when only an input cable is present.
4. Voltage is getting to the board, but I'm getting no voltage reads on the transistor drains (should read 4.5v - they require biasing from the trim pots, but the pots don't seem to do anything) when I use the ground lug on the PCB. If I put the negative lead of my DMM on the ground of the battery and then test the drain pin, it reads the full 9.2v.

I've checked an rechecked the wiring diagram and I'm fairly certain the wires are at least all going to the right places.
Any ideas?

Here's the schem: http://www.runoffgroove.com/matchbox.html

And here's the build guide: http://www.olcircuits.com/documents2008/olc_matchbox_buildguide.pdf

[tcr77]

Just checked the voltages at the transistors again, and even with the trim pots turned all the way up, I'm only getting .6v on the DMM.

Also, according the the build guide, D1 (an LED) should not light up, but it does. Is that a problem?

[tcr77]

In true bypass mode, does the signal leave the output jack thru the tip or the sleeve? Just trying to get the bypass setting to work first, and then see about troubleshooting the board if necessary. Thanks!

[jkokura]

The tip of both jacks are used for both bypass and when effect is engaged.

The sleeves are used for grounding the circuit.

Have you seen the debugging page that's a sticky in this forum? It will help guide you to give us the information we need so we can help you. However I can tell you that if there's no signal in bypass mode that it's likely your wiring is wrong or you have a faulty part (switch, jack, wire). If your led only lights up when you have something in the output jack, it's likely you have the LED grounded to that jack. Pictures and the debugging info will help us greatly past that information.

Also, one other note is that when you look at the guts of a pedal, everything is backwards from when it's knobs are up. remember that if you want the 'input' on the right side when it's knob side up, when you flip it over to work on the inside that the input jack is now on your left side, not the right.

I know you've rechecked your wiring, but it's either that or the parts, and it's more likely to be human error over part error in this case.

Jacob

[PRR]

> no voltage reads on the transistor drains ...when I use the ground lug on the PCB. If I put the negative lead of my DMM on the ground of the battery and then test the drain pin, it reads the full 9.2v.

It should read the SAME from PCB Gnd or from Battery Negative. The B- is supposed to be connected to PCB Gnd. Yours apparently isn't.

OH! Be sure you stick a standard guitar plug in the IN jack. They use the plug body to connect power - to PCB Gnd. (But you say "no signal", so you musta done this?)

Re-follow the blue and black wires on page 20 and 23.

> LED will only light up when a cable is plugged into the output jack. It won't light up when only an input cable is present.

Is it possible the IN and OUT jacks are trading places?

{I guess Jakob is saying the same things...}

[tcr77]

Ok, so I've got signal passing thru in true bypass mode (bad set of lugs on the input jack) and the DC/battery issue is fixed too.

However, I'm still not getting any signal when the effect is engaged. Voltage on Q2 and Q3 read:

Q1- (fixed voltage)
1 - 9.0v
2 - 1.6v
3 - 0.0v

Q2 - variable
1 - 4.4v
2 - 0.55v
3 - 0.4v

Q3 - variable
1 - 4.6v
2 - 0.01v
3 - 0.0v

[PRR]

> Q1- (fixed voltage)
> 1 - 9.0v

That ain't right. And the 1.6V is suggestive.

Lift one leg of D1 out of the PCB. If that "9.0V" is now 4V or 5V, take D1 all the way out, turn it around, replace.

[tcr77]

> Q1- (fixed voltage)
> 1 - 9.0v


Lift one leg of D1 out of the PCB. If that "9.0V" is now 4V or 5V, take D1 all the way out, turn it around, replace.

You, sir, are a genius. Thanks everybody! It works and sounds awesome now.

[jkokura]

I done the backwards power Diode once or twice. Often they blow and send the 9V to ground, causing mayhem and frustration.

Glad you got it fixed, post some pics when it's 'finished.'

Jacob

[tcr77]

Thanks for the help guys. Here it is all put together:



















It sounds awesome, too! Will post sound clips one of these days.

[PRR]

> You, sir, are a genius.

No. This is simple carpentry.

OK, if you ever built a house you know that carpentry is not simple.

I been watching a couple guys build an addition. It's all stacking 9.25", 5.5", 1.5", 0.75" building blocks (2x10, 2x6, 2-by, boards). When something comes out 1.5" off, you must have left-out or stuck-in a 2-by somewhere.

> Q1-
2 - 1.6v

When stacking electronics, a forward (lit-up) LED is a handy 1.6V stacking-block.

However this LED is not going to light, and is not "forward" in normal operation. It is really more like the 2-by block I stuck on the bathroom wall so the doorknob doesn't bust the mirror. It "catches" excess/wrong voltage so the MOSFET gate-glass doesn't get broken. In normal operation it "doesn't matter", has no effect.

So you put in a 1.6V "block", but then the door doesn't work, misses the latch by 1.6V. In carpentry, you would SEE that the block should go the other way (to the mirror, not the latch side). Electronics, you can't SEE, but a blind man with a braille tape measure could "see" the problem in his head. (And in this case, you SAW the LED light up.... you were on the right track.)

Not genius. Just too many years of stacking-up 0.6V, 1.6V, 5.9V, 12V etc in my head.

[Guitartoma]

Hey there -
I'm in the midst of building a Matchbox. C3 calls for a 360pF cap, which I can't find anywhere. Looking at your pictures - it looks like you used a 330pF, is that right? Did you vary anywhere else from the original schematic?
Thanks,
-Tom