weird Boss SD-1 problem

[Nuts]

Hi,
When the guitar volume pot is in full, there ain't no sound whether the pedal is on or off.
When I roll the volume in the guitar to down past 8, the pedal works as usual.
What is it ?
Thanks,
Nuts.

[miqbal]

Hey Nuts, is the pedal yours? You're the stompbox guy, why don't you take off the pot and try with a brand new one?

[Nuts]

   Stompbox guy ? I'm only a subscriber to "Wampler Pedals" ...  if that's the reason why you called me like that
If I was him I probably knew how to fix it myself ... 

The pedal is not mine...
But the volume pot of the guitar is fine, I check it with another guitar, and cheack the guitar itself, it was fine.
Only when the pedal is plugged ...

[MKB]

That's a strange problem indeed, I can't think of anything that might cause that other than a flaky volume pot in the guitar (my Ibanez does stuff like that as the volume pots are going bad).  What specifically are the guitars you are using in the pedal?  If the one that works is a Strat and the one that doesn't is a Gibson, maybe it is something to do with the impedance of the guitar pots and pickups and how they affect the pedal.  And you might try the guitar that causes the SD-1 to act up with another Boss pedal to see if the same thing happens with it.  Most Boss pedals have electronic switching, which means they all have similar input and output buffer circuitry.

[Nuts]

That's a strange problem indeed, I can't think of anything that might cause that other than a flaky volume pot in the guitar (my Ibanez does stuff like that as the volume pots are going bad).  What specifically are the guitars you are using in the pedal?  If the one that works is a Strat and the one that doesn't is a Gibson, maybe it is something to do with the impedance of the guitar pots and pickups and how they affect the pedal.  And you might try the guitar that causes the SD-1 to act up with another Boss pedal to see if the same thing happens with it.  Most Boss pedals have electronic switching, which means they all have similar input and output buffer circuitry.

No no, It's happenning with both guitars.
I have my own SD-1 , and it works great.
the problem is for sure from the specific pedal...

[miqbal]

But the volume pot of the guitar is fine.................

Thought it was the pedal pot , I must had read it soooo fast..

[Nuts]

[Sock Puppet]

Faulty/shorted 47n input cap draining the transistor bias through the 6k or so pickup impedance?

What voltage is on the transistor base?

S.

[Nuts]

3.8

[Nuts]

  Still not sloved, I'm trying for the last time to bump for help

[miqbal]

Can you do the audio probing  at the emitter pin of transistor Q5 (it's the first transistor at the input buffer section)?? Is is still the same?? If yes, you might have to replace that transistor.

[Nuts]

So I replaced Q5 with transistor fom my own SD-1 but no succses...
What another parts looks suspicious ?

[miqbal]

I have uploded my SD-1 schematic here, so we can get the same orientation. The component number shown on the schematic should be in accordance with the component number on your SD-1 PCB.

http://aronnelson.com/gallery/d/18736-1/SD-1_sch_iqb.gif

Ok, we will try to isolate the problem, I'm afraid you will have to deal with some soldering and de-soldering some components.

If you don't mind: remove C18(18n) and R11(22k).

By doing this, we have cut the fx-ed signal. The clean signal signal shall not be interfered by the fx circuitry.
Test the pedal again (You will not be able to hear the fx signal). How is the pedal with ONLY the clean signal?

If the result is OK, something has gone wrong with the fx circutry.
If the result is still the same, the problem might reside at the clean signal path... OR ... the FET switching ... OR ... both.

[Nuts]

O now it's even more weird.
only having a signal when I'm in 7-8 on the volume.
so the problem is in the clean signal path or the FET or both

[miqbal]

Have you done per my suggestion, i.e, removing C18 and R11 bla,bla...?

[Nuts]

yes.
But I reconnect these parts and there's no sound at all 
the worst luck I ever had with pedals....

[ibodog]

A year later on this thread, but I'm having the exact same problem as the original poster!

I did the "fulltone" sound-alike mod and socketed the IC and replaced the LED with a small blue one.  When I turn up the guitar volume knob I get a "scratchy" sound.  But I get no volume when the guitar volume is below 4 or above 8.  Set in the middle and don't move the guitar volume and the effect sounds OK.  I get the same problem whether the pedal is bypassed or engaged.  Guitar volume on the telecaster is fine straight to the amp and my other SD-1 has no similar problem.  In the socketed IC I tried 2 different chips but had the same problem with each one.

Anyone want to pick up this thread and give me a hand?

[German]

Hey you have active or passive bypass in your SD?
Try to connect from start - with turned guitar volume pot at full
I mean so - connect a wire ot the output jack and connect it to - input.. then to buffer, then after it.
And tell us then, where the signal is broken.

[ibodog]

Thanks for the reply, German.  I'm not sure if I follow what you want me to try out.  This SD-1 was new/stock before I added the fulltone mod.  I've also tacked on the bypass solution posted elsewhere (cap, diode, transistor) but it didn't seem to make a difference in this problem OR in getting the effected sound to go away when in bypass.

[ibodog]

In case anyone ever wonders, the fix is to check your R6 and C1 parts and make sure they aren't shorted together.  I replaced both parts on my SD-1 and now the pedal works OK with no similar problem.