Fixing a Boss SD2

[tomer629]

I'm trying to fix Boss SD2 Dual Overdrive. I messed with it many years ago when it first quit working, and I'm pretty sure I wired it up wrong. Anyway there seems to be a severe shortage of gutshots of this pedal online. I only found a handful, and they were low quality and didn't have enough angles for me to see how its wired.

So if anyone has some gutshots or could shed some light on how these are wired up it would be greatly appreciated.


I did find this: http://www.aronnelson.com/gallery/main.php/v/KHE/Boss_SD2_schematic.jpg.html?g2_imageViewsIndex=1

But that is even more confusing to me than a schematic (which I also found but it doesn't show off board wiring).

[Hatredman]

How about a gutshot of yours?

[tomer629]

Here is mine:

http://imgur.com/a/7vBCg - remember the wiring probably wrong. I tried to fix it over 10 years ago when I knew absolutely nothing about pedals.




I get no sound with it on or in bypass. Well some noise that increases if I move the gain/volume knobs. No guitar signal.

Also the green led works as expected, but the red only flickers when I play with the footswitch. If i screw with it long enough I can get it to stay on.


One thing I thought was weird with this pedal: The Yellow wires. Two wires come off the board but it appears that only the white connects to anything. At least thats how the one on the right was wired to the footswitch. The one on the left with the green shrink tubing is the one I soldered to the input jack because it was loose. Why have 2 wires coming off the board if only one is connected to something? I guess now that I think about it, is that black wire just for shielding the input and output? It is a bare wire wrapped around the white wire under the yellow shrink tubing.


Before someone asks about the bare black wire coming off the green shrink wrapped wire... this is connected to the black wire coming off the board (the one wrapped around the white wire). I did that because I wasn't sure if its supposed to go to something so I left it out to poke around with and see if I could get any sound. I couldnt.

I did notice, if I short out the pcb on the case, all the LEDs on the board flicker for a second. I hope this didnt damage anything because it happened a bunch of times before I figured out what it was. At first I thought it was a loose wire.


Any input or tips on how to troubleshoot an old Boss pedal like this would be awesome. I got this pedal almost 20 years ago with my first guitar, so it has some sentimental value to me and I really want to get it working.

[Groovenut]

according to the schematic in the link posted, there are 6 wires coming off the main board.

#2 goes to the footswitch

#3 looks like it goes to both the center pin on the dc jack and the negative wire on the battery clip

#4 goes to the positive on the battery and the switch on the dc jack

#5 (I think thats a 5 on the schematic, might be an 8 ) goes to the tip on the input jack

#6 goes to the tip on the output jack

#7 goes to the ground on the input jack

There is 2 number 1 wires. One goes to the remote jack. The other I believe is part of the 12 lead ribbon wire connector. The schematic says they are both from the daughter board.

The pics are not really much help because they fail to show the main board connections. If you can do a few that show the wire connection to the main pcb that will help.

maybe this is enough info to get you started

[tomer629]

Thanks Groovenut. I think you got me on the right track. After reading your post I went back and looked at the schematic...I totally missed the outer ring of #'s. I was looking at the inner ring which also has connections numbered 1-8.

It makes sense now and it looks like I do have a few things wired wrong. Cant wait to try it tomorrow.

[tomer629]

Got it working! Both channels work.

But its very fuzzy on both channels. Doesn't really sound like the videos I've seen. Its like there is a layer of fuzz over the normal sound of the pedal. Its the same on both channels.

Anyone got any ideas?

[Groovenut]

check the voltage at pins 3 and 5 of both IC's. It should be around 4.5vdc

If the bias voltage is off significantly the opamps are clipping one side of the waveform and will sound very fuzzy.

Just a guess though

[tomer629]

IC1 is the 14Pin. Voltage at Pin 3 is 0. Pin 5 is 8.42


ICs 2, 3, and 4 are the single row 8 pin ones.

Voltage at pin 3 is around 4.24 for all. Is that too low?

I measured these with the red lead on the IC, and the black lead on the case.


Could this be caused by bad electrolytics? The pedal is around 20 years old. There is a definite fizzyness over the tone. Comparing to reviews on youtube it I'm 99% sure that fizzyness shouldnt be there. I'll try to make some recordings with it.

[Groovenut]

electrolytics could definitely be an issue. Check the junction of R61, R44, an C45 it should be 4.5vdc

The 14 pin chip is part of the switching and mode switch. The SIL chips should mostly read ~4.5vdc on all pins but 4 & 8. * should be power rail @9vdc, 4 should be ground @0

[ElectricDruid]

electrolytics could definitely be an issue. Check the junction of R61, R44, an C45 it should be 4.5vdc

The 14 pin chip is part of the switching and mode switch. The SIL chips should mostly read ~4.5vdc on all pins but 4 & 8. * should be power rail @9vdc, 4 should be ground @0

Electrolytics *could* be an issue, but it's not that likely. Not after 20 years. I've got plenty of bits of kit hanging around that are older than that and they're still fine. And I bet many people here are in the same boat.

I'd only replace an electrolytic if you've *proved* that it's faulty. Otherwise it's just shooting into the darkness, and you'd be highly likely to kill something important, rather than hit the target. Sorry, are my metaphors getting out of hand?!

I'd keep looking for a more likely cause for the time being. I'd suspect a broken ground connection. If the "ground" level floats, you can get the fuzzy noise you describe - like the proper sound of the pedal is "lost" inside a load of noise.

HTH,
Tom

[Ry]

Sorry to Frankenpost on this old thread, but I'm having this same issue with one of these pedals.  It originally switched between red and green channels when I tried to switch them, so I replaced the 4011, now I can use the green channel, but the red is slient when switched on.  I did poke around on the board a bit and noticed that the red channel would sometimes work briefly (fades out quickly to silence) when I touched pins 1&2 of the 4011.  Looking at the schematic, I'm thinking my next stop is with the R6/C23 combo.  Any other thoughts are appreciated!