BAHH! Help!

[Guitarfreak]

I was doing the tone bypass mod on my EXH Big Muff and while drilling I hit into a resistor which I think damaged it because now that the pedal is assembled again it is cutting out and crackly.  It is the resistor that is directly between the tone and sustain pots about three quarters of an inch down, it's right at the top of the board.  I don't know how to read a schematic so I don't know what value that resistor was.  Can anyone help me?

http://www.pisotones.com/BigMuffPi/psst/schm-american.jpeg

[jacobyjd]

Since layouts vary, we can't tell what resistor you're referring to on the board based on the schematic. You'll need to post pictures of the front and back of the board so we can see the traces.

[Guitarfreak]

Alright I'll see what kind of pictures I can get of it.  In the meantime though, do you think it could be my soldering on the new component that is causing the cutouts/crackliness?

[jacobyjd]

It's very possible--if you damaged a resistor, it could either cut out completely, mis-bias something, or cause intermittent problems.

Other possibilities could involve an overstressed lead (from taking it in/out of the box), or a broken lead. Too much heat from soldering could have damaged the transistors, etc.

[Guitarfreak]

OK, so you think it is definitely the resistor that is the problem in this case?  That's good news.  A side question, are you familiar with this mod?  It supposedly bypasses the tone pot and the way I wired it is not the way that it makes the most sense to me to wire it, I just tried to follow the site's directions as closely as possible.  My tone pot's extended lugs are connected directly to the board with no wires interfacing them.  I soldered wires from the backside of the board to the new component switch disregarding the lugs completely because the mod made no mention of it.  It would make sense to me to cut those lugs connections and force the tone pot to interface to the board THROUGH the mini switch for full effect correct?

[Guitarfreak]

Here is the mod that I followed if it helps.
http://docs.google.com/present/embed?size=l&id=dhrp52kc_14rg8b3gm

Thanks for the quick response BTW

[Guitarfreak]

ALright, well instead of replacing the original value resistor, I might as well go ahead and make a mod project out of it.  Does anyone know of any cool mods that increase frequency response and fidelity of the circuit while taking some noise out at the same time?  Maybe make it smoother or give it more of that tube-sag sound if possible?  Lessen the EQ mid scoop?  I've found that the creamy dreamer mod is very popular, but does it do what I want it to do?  I also can't find any specifics on the mod itself, a lot of old links seem to be broken, although I did hear someone say to replace all resistors with 15k resistors.  Is it that simple?

[jacobyjd]

There's no use in modding it unless you can fix the current problem. Additionally, it would be better for you to learn more about reading schematics before you attempt new mods.

[Guitarfreak]

I hate it when you are right.  I've done a good deal of guitar electronics modding, but I don't yet understand circuit board signal flow yet or how it relates to a schematic.  I know that the signal flow has got something to do with the traces, but I don't know much more than that.  How can I learn this?  Is there well respected literature on the matter that I should look into picking up?

[jacobyjd]

Well, there are a ton of resources, but if you're at the absolute beginner level for reading schematics and whatnot, any literature can easily get confusing. By far, the best thing to do is to take a hands-on approach.

Fortunately, you have the advantage of being elbows-deep in a project that needs debugging

The first thing to do would be to acquire the schematic (linked above), then determine which parts are which.

Photos of your board (or some other indication of the resistor that's burned) would still be helpful, since I can't give you any help with the problem until I know which resistor in particular is damaged.

From there, though, we can take a methodical approach to debugging the circuit--which will take a lot of applying the board/parts to the schematic. We can explain some things along the way

[Guitarfreak]

Fortunately, you have the advantage of being elbows-deep in a project that needs debugging

You and I have different ways of describing things

Here is a pic, the damaged resistor is the outlined.  Sorry it took so long, I was making a comparison clip.  BTW if you couldn't tell from the clip the Muff works now, but considering the resistor is still quite damaged I am still going to replace/mod it.



Here is the clip if anyone is interested, not really pertinent to the thread at hand, but I made it so why not post it anyway
http://soundclick.com/share?songid=8611646

[aron]

IF that middle pot is the tone pot, then it's the 22K resistor to ground - well that's my guess.

[jacobyjd]

IF that middle pot is the tone pot, then it's the 22K resistor to ground - well that's my guess.

Mind too

[Guitarfreak]

So any component that leaves a trace whose destination is not the same or different trace is said to go to ground then?  Now what was the thought process behind the conclusion?

[jacobyjd]

We're looking at it using the schematic as a map--

Assuming the tone pot is the middle one (that's likely, since that's where your mod is installed), we can assume that the resistor connects to one of the lugs of the tone pot.

Knowing that the other end of the resistor connects to a pot leg (opposite the orientation of the pot leg the other end of the resistor is connected to--either the tone or sustain pot), and seeing that the pot's lug only has 1 other connection to its trace (a resistor, based on its spacing), we can guess that the pot in question is the sustain pot (which connects to ground on the schematic via a 1k8 resistor), and that this end of the damaged resistor connects to ground.

From there, knowing that it's a resistor going straight to ground from one of the outside lugs of the tone pot, we can see that there's only one connection like this: the 22k resistor to ground

[Guitarfreak]

I guess the more you look at them the better huh?  How about we try it with a BOSS SD-1, because the traces and components are all individually labeled so I think it would be easier to come to an understanding from there.







I am looking at the schematic and trying to find the .047uf capacitor, which is in the input section so I start with trace 1 and follow it to the first component which is a resistor R2... which makes no sense to me.

Then I thought maybe trace 1 isn't really the first trace.  So I followed all three wires which come from the input jack (for not knowing which wire is which) and followed THOSE traces to the first component.  None of which were a capacitor.  I do see C1, but I fail to see how it is the first component in the schematic/signal flow by any means.

[Kearns892]

Hmmm, since you didn't specify which pad the input is leading to, I'm not sure. Butt I must say, I don't think your schematic matches the board you are looking at. A quick count reveals 1 transistor on the schematic and i believe I see 6 on the board. 3 Diodes on your schematic  and at least 7 on the board. Try reading "From Schematic to Reality" you can find it on Beavisaudio.com its a very helpful introductory read into this sort of thing.

[FiveseveN]

I don't think your schematic matches the board you are looking at

The schematic doesn't include the electronic bypassing.

[Guitarfreak]

How about this one?

[jonasx26]

http://www.godiksennet.com/images/sch/SD1PG2.JPG

i used this schematic and layout while modding my oldie SD-1.
current production models probably don't use the same layout.

might be helpful anyways. google service notes.