Russian Muff problems

[nieh]

So today I was in a local shop and the owner gave me a free black Sovtek BMP because I had been looking at it a few weeks ago and it was broken and he didn't wan't to fix it. The tone and sustain knob work like they should, but when the pedal is off there is barley and dry signal coming out, and when I engage the pedal, I have to turn the volume all the way up to barley hear anything. any ideas of whats wrong?

[Scruffie]

You need an audio probe! (Debugging section of DIYStompboxes) But i'm gunna say switch, jacks or volume pot.

The Black Sovtek BMP Should be true bypass but due to a wiring mistake they're not, you need to cut a track and re locate a wire... just so you know.

[nieh]

It's not the volume pot. How do I make it true bypass?

[Scruffie]

It's not the volume pot. How do I make it true bypass?

I'm trying to remember, one of the jacks is connected to the circuit through a trace that shouldn't be... I think it's the input jacks tip, you need to cut the trace and move the input wire... they left it like it was before they started using 3PDTs.

Here we go http://img297.imageshack.us/img297/9403 ... fftbd2.jpg knew i'd seen a picture of it before.

This is assuming you have the later version with the 3PDT already installed.

[nieh]

It's not the volume pot. How do I make it true bypass?

I'm trying to remember, one of the jacks is connected to the circuit through a trace that shouldn't be... I think it's the input jacks tip, you need to cut the trace and move the input wire... they left it like it was before they started using 3PDTs.

Here we go http://img297.imageshack.us/img297/9403 ... fftbd2.jpg knew i'd seen a picture of it before.

This is assuming you have the later version with the 3PDT already installed.

Mine has a switch with 6 lugs.

[Scruffie]

It's not the volume pot. How do I make it true bypass?

I'm trying to remember, one of the jacks is connected to the circuit through a trace that shouldn't be... I think it's the input jacks tip, you need to cut the trace and move the input wire... they left it like it was before they started using 3PDTs.

Here we go http://img297.imageshack.us/img297/9403 ... fftbd2.jpg knew i'd seen a picture of it before.

This is assuming you have the later version with the 3PDT already installed.

Mine has a switch with 6 lugs.

Then it is not true bypass... you'll have to either replace the switch with a 3PDT or loose the LED... or wire up a millenium bypass.

Not being true bypass means the problem may be in circuit, here's the audio probe link - http://www.diystompboxes.com/wiki/index ... =Debugging

[devnulljp]

I'll lay you odds the switch is shagged.
Replace it.
Wiring scheme is weird IIRC so careful how you do it.
Might as well TB it. Here's how.
http://www.singlecoil.com/docs/russian_muff.pdf

[nieh]

I'm going to add true bypass. See if that works.

[nieh]

Pedal is true bypass, problem persists.

[Schlatte]

Could there be a low resistance/low impedance load that sucks the output to near ground?

[Scruffie]

If I was going to just go blindly and not use the audio probe, i'd replace the switch as you have, make sure the jacks are clean and making good contact, then probably just resolder every joint on the board.

Measure every transistors voltages and post them here, does this version have electrolytics? Replace them all.

This is all blind guessing though without signal tracing and voltages.

[nieh]

I still can't get it to work. How do I use the audio probe?

[Schlatte]

I still can't get it to work. How do I use the audio probe?

just grab a capacitor and a cable you plug into your amp... using crocodile connectors or something similar connect the tip of your cable to one leg of the capacitor and the sleeve of your cable to the ground of your pedal... if you decide to use an el-cap you have to make sure the negative leg is connected to the tip of the cable...

with the other leg you just poke on different points on the pcb... I always start at the input jack and work my way through.. make sure to try every collector of every tranny!
Btw- you have to feed some signal to the pedal in order to make this trick work - so just use a sine-wave generator or your guitar/bass...

[devnulljp]

bad volume pot?

There's a hierarchy of craptastic components in those things starting with the switch (which you've replaced), the pots, the jacks ...
Then I'd look at solder joints that might have been stressed -- like those around the jacks.

[eatyourguitar]

I would be checking voltages before the probe. if you have pretty close to 9v or 0v at any collectors. if any of your base voltages are below 0.7v. set the meter to capacitance and test the electrolytic caps. try it with the meter probes both ways. they are polarized caps. I was working on a russian muff and I was surprised that the grounded input in bypass mode is actually grounding the input of the 3rd transistor. I guess they figured it was more quiet than grounding the real input of the board.