Boss SD-1 From the dead.. and it is still dead. Sort of. Help. R1 / C1 / Q5

[Saturnine10]

Ah jeez, i have been racking my brains over this damn SD1 to work properly and finally here i am posting about it to see if i can get some help!

Alrighty, probably 5 years ago I modded said SD1 and it never worked properly.  Didn't want to deal with it so i put it back in the box.  Fast forward to this beervirus situation and I have some time on my hands to get this thing working again.  I think they are the Wampler mods,

The problem is that.. when plugged in it works but sounds like it is literally under 80ft of mud.  Not even talking about the C6 mod, like serious it sounds like it is under a crap ton of mud. 

Busted out the meter, made an audio probe and I have been geeking out for the last few days trying to figure what the f-ck is going on. 

TEST RIG:  Ipad (for music generation) --> Input of SD1--> Probe (output) -->Boss MA1 --> Headphones.  Power to pedals is PP2+

Following the input signal into the board, i seem to run into my issue almost right away.  PLOT THICKENS

Input to the PCB is #3, then runs into the R1 10k then the C1 .047 then to Q5.  I get crystal clear audio at point #3, both sides of the 10k and the first leg of C1.  Second leg of C1 is when the signal becomes super muddy.  This signal then goes into the base of Q5. 

I have tried at least 5-6 different combos of R1 / C1 and they all have the same result -- The signal leading into the bast of Q5 is super muddy.  I've tried rewiring C1 first, then R1 and still the same result.  I dont see any mucked up traces or evidence that the PCB is shorting out etc. 

I should also mention that I have a second stock SD1 that i am checking against in the same manor -- audio probe is clear all through and past Q5. 

Voltages seem to be correct across the board, nothing is wonky.  Base of Q5 is getting 8.5v (which is what is coming off the DC jack), Collector is getting 4.2v, Emmiter is getting 3.6v

Pics:   









I'm at a loss

[Rob Strand]

Voltages seem to be correct across the board, nothing is wonky.  Base of Q5 is getting 8.5v (which is what is coming off the DC jack), Collector is getting 4.2v, Emmiter is getting 3.6v

Your text here might have Base and Collection swapped.  Japanese transistors order the pins /BCE\ not /CBE\ ; from bottom view.

It is highly likely the problem isn't that it passes through a part then stops at the faulty part.  What can happen is the following circuit has a problem and that problem shorts out the signal.  That's why playing with C1, R1 hasn't helped.

The simple answer might be your Q5 is fried but your DC voltages look OK so perhaps look for a problem further into the circuit.

I'd be looking at shorts around C2, R4, IC pin5, then C9, Q2  and maybe even R13, R14.

One approach would be to lift one leg of C2 then see if the signal at the emitter of Q5 comes good.  That implies the problem is between C2 and IC pin 5.  If the signal is still bad try *also* lifting one leg of C9.  If it comes good then the problem is likely to be somewhere from C9 and beyond.


One question is the problem present in both Effect and non-Effect mode?


For reference:
https://www.hobby-hour.com/electronics/s/sd1-super-overdrive.php


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Edit/Fix:  C2 previously mistyped as C12