Boss OD--1. Need help with repair. no effected output.

[Mr.Grim]

Hello, I am trying to repair an original OD-1 for a friend.

When engaged, there is no effect. It passes a weak dry signal that is unison when level is maxed out.  All results are same with adapter or 9V battery.

Board and all wire connections are fine. Nothing seems blown visually. No bad solder joints or loose wires.

Here are my voltages

RC3403ADB
1- 4.47
2- 4.47
3- 4.37
4- 8.95
5- 4.45
6- 4.46
7- 4.43
8- 4.5
9- 4.46
10- 4.46
11- 0
12- 4.27
13- 4.48
14- 4.48

Q1 2SK30A
S- 4.45
G- 0.02
S- 4.45

Q2 2SK30A
S- 4.25
G- 0
S- 4.45

Q3 2SC536
E- 0.53
C- 0.56
B- 1.12

Q4 2SC536
E- 0.53
C- 6.11
B- 0.19

Please help! Much thanks in advance!

[fowl]

I think your voltages look correct.

I hope you get it running, that is the most collectible version of the OD-1, with the Raytheon chip and 1S2473 diodes.  Fresh electrolytics would not be a bad idea in a pedal of that age, and there's nothing at all special about the originals.  Short of that, build an audio probe and trace the signal path.

[Mr.Grim]

Thanks for the suggestions. I actually did replace all the E caps rite before taking this photo. It's the only components I want ahead and replaced right off the bat.   I'm going to look in to the audio probe.

BTW loving this quiz to post thing.

[fowl]

BTW loving this quiz to post thing.

I think that goes away after 5 posts.

[anotherjim]

The FET switching doesn't totally stop a little signal leaking through from the dry bypass signal path. So, you may have a break in the effect signal path. If not a wire, then the output volume pot might be damaged - sometimes an accidental heavy foot stomp on the knob can push the pot shaft down and cause damage.
I found a partial schematic if that helps...

It doesn't show the bypass control circuit. Now, Q1 and Q2 should have opposite gate controls, when one is on, the other must be off. You have 0v for both gates. We shall have to think about that...

[anotherjim]

For reference, here a later OD-1 showing the bypass control...

To get a better idea of what the bypass is doing, check the voltages at the cathode end of the diodes for Q1 & Q2 gate controls. They should be different and swap over when you press the footswitch.

[Mark Hammer]

1) The original (RC3403 instead of 4558) is a great little overdrive.  Needs a little more bottom,which can be achieved by making C3 a little larger.  But aside from that, just right.

2) For reasons I don't comprehend, FETs can go bad.  The way to test if this has happened is to simply bypass the bypass by soldering/tacking on a wire, on the copper side of the board, from the output of the volume pot to the cap after the switching FET.  If that restores effect volume, then you have a bad FET, and replacing it will fix the problem...probably.

[fowl]

1) The original (RC3403 instead of 4558) is a great little overdrive.  Needs a little more bottom,which can be achieved by making C3 a little larger.

I might have to try that on my clone (JRC3403).  100n?  68n?

[Rob Strand]

It would short-cut a lot of debugging if you listened to the output of each opamp.  Perhaps the overdrive stage (with the diodes) has an issue, or, the level pot is old/damaged and no signal is coming out of the wiper.   You would expect hear overdrive somewhere along the middle section of opamps.

[Mark Hammer]

1) The original (RC3403 instead of 4558) is a great little overdrive.  Needs a little more bottom,which can be achieved by making C3 a little larger.

I might have to try that on my clone (JRC3403).  100n?  68n?

Either of those will be fine.  Some folks go for even larger values, like 220nf.  The thing to consider is that lower notes on thicker strings will have a higher amplitude, resulting in more clipping (i.e., being at or above the clipping threshold more often and for longer).  The greater distortion at the low end of the fretboard kind of changes the personality of the pedal, potentially in unwanted ways.  The compromise is to move the low-end rolloff downwards, but not too much, such that you get a little more meat and substance, but still retain the basic character of the pedal.  Stock rolloff (47nf) is 720hz.  Raising the cap to 68nf moves the rolloff down to around 500hz, and raising it to 100nf bumps it down further to just under 340hz.

Since an "ideal" value can vary with the guitar and pickups used, sometimes the sensible thing to do is begin with stock value, and temporarily tack on parallel caps on the copper side of the board to find what you like.  Then remove the stock one and install whatever common value comes closest to the tone you liked.

[fowl]

^ Right on, I like the pedal as it is, but it could do with just a bit more bottom for my rig.  I might just try 68n without experimenting.  With stock values, it's very similar to a tube screamer, and I've been digging the Analogman "Silver Mod" (my diy copy) in those, which is mostly a subtle increase in bass.

Edit:  I changed my mind.  This is a perf build, partially gooped with hot glue (for strength, not secrecy), so it was massively easier to just tack a little 22n ceramic disc in parallel on the back of the board.  And also easier to remove or change if I'm not satisfied with it.  I'll test it out at a more decent hour.

Edit 2:  47n to ~69n is very subtle indeed.  Just a slightly chunkier version of the same thing.  100n woulld probably sound nice.

[Mr.Grim]

Ok guys, sorry for the delay. Life has been in the way.  Anyway, finally have time to work on this.

Ok so I've worked as an electrical engineer, (never audio related unfortunately) and have been building my own pedals seriously for maybe 8ish years, but started an interest when I was 13 and requested a copy of C.A.'s Electronic Projects for Musicians for x-mas (I'm 41 now and have owned 3 battered copy's)

But at work, or at home on my own projects I've always gotten severely lucky And have not had much trouble with anything I built. I've been told I've got very good soldering skills, but I honestly think that's B.S. all anyone has to do is pay attention.

What I'm getting down to is that I don't have a damn clue what I'm doing on a repair end of things at all. I understand an audio probe but until this moment have never had to use one. So I built one, and a little wave generator to give me a signal. And I found a copy of what I think is the correct info for this model.  I've been poking around and I'm lost.

I know it's hard to point me in the right direction without being here next to me but does anyone have any tips to help me out?

[Mr.Grim]

Oh a big part is I'm not sure where audio is saposed to be and where it's not.  And it's taking me a bit to get around reading the schematic, I'm not used to seeing the op amp split apart, but I'm getting it.

Any specific points I should be poking at?

[fowl]

The 3403 is a quad opamp.  I would first check for signal at the output of each of those four sections, pins 1, 7, 8, and 14.  That should narrow the trouble down to a small section of the circuit.

[Mr.Grim]

I get signal on all 4 pins advised.

[fowl]

Well that's good.  According to the schematic, there's only 3 parts between pin 14 and the output jack.  You already replaced the output cap C9.  So check that R13 isn't open, and that R14 isn't shorted.

[Mr.Grim]

Ok well I seem to get a signal all the way through. An I thought that was odd so I tried again turning it on and off and noticed that the signal I was getting from pin 14 is the very weak signal I was originally getting. My amp was just jacked up and so I didn't noticed until I used the switch and was startled by the loud bypass.

Pin 8 is slightly louder than 14, and pins 1/4 are loud like bypass. 14 is very quiet.

Bad chip? Voltage issue?

[fowl]

Notice there's a volume pot after pin 8.  Is it turned up or down?

How loud at pin 9?

[Mr.Grim]

The faint sound I get is the same as my original post when the pot is full on. When turned down I get nothing.

There is no audio at all on pin 9.

[fowl]

The faint sound I get is the same as my original post when the pot is full on. When turned down I get nothing.

There is no audio at all on pin 9.

I hope the schematic above agrees with the unit you're working on, as far as pin and part numbers go.  But check both sides of R8, a 10K that connects between pins 7 and 9.  If you have good volume on the pin 7 end, maybe that resistor is bad.