Home › Forums › Vintage EHX › Black Russian Big Muff no sound when activated

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  • October 30, 2021 at 5:55 pm #186168
    Minor_Issue
    Participant

    I bought a Black Russian Big Muff. When I got it, it was operating normally but two of the pots (sust. and tone) were jammed and not turning. Sound was otherwise perfect and sounded great.

    I decided to replace them with these which I saw on a forum post here:
    https://smallbear-electronics.mybigcommerce.com/poteniometer-for-russian-big-muff-work-alike/

    I checked my solder job against the schematic and everything appears correctly wired, but now when I turn it on there’s no sound and the LED light is not turning on. In bypass mode guitar signal works fine.

    Looking for troubleshooting advice. I hope there’s not something wrong with the new pots and their values. It seems like the circuit is not activating correctly or else the LED indicator would turn on.

    My knowledge of circuitry is fairly rudimentary so please educate me! Thank you all.

    October 31, 2021 at 8:02 am #186172
    j_flanders
    Participant

    It’s always best to take pictures of the stock unit and then do the repair according to that.
    You are referring to a schematic. Which schematic and on what site?
    If you’re using the schematics from Kitrae’s site, then that could be the cause for it not working. Some of his schematics are fundamentally wrong. IIRC especially the one for the Black Russian(s).
    I have several Black Russian Big Muff Pi’s. I can take some pictures if you like. Maybe you can find some pictures of the wiring online as well.

    • This reply was modified 3 years ago by j_flanders.
    October 31, 2021 at 11:47 am #186174
    j_flanders
    Participant

    Edit:
    It seems, since I last checked and posted about the errors on diystompboxes.com, some corrections have been made to the schematic for the Black Russian BMP.
    The LED part is still wrong though.

    October 31, 2021 at 12:22 pm #186175
    Minor_Issue
    Participant

    I didn’t touch the LED or the switch when I wired it. Only things I soldered were the two pots (S, T). As far as I know the circuit is correct but I could obviously be wrong. For clarification I did copy off the stock unit, then I checked against the schematic.

    View post on imgur.com

    October 31, 2021 at 3:04 pm #186179
    j_flanders
    Participant

    If you didn’t touch the switch, nor the LED and you have sound in bypass mode the only thing I think of is that the 9V is not getting to the board.
    Check the battery snap and if you have a multimeter check if the LED gets its 9V.
    Make sure you have a guitar cable inserted into the input jack of the pedal when testing because that input switches the battery on/off when a jack is inserted/pulled.

    October 31, 2021 at 3:10 pm #186180
    Minor_Issue
    Participant

    Ok, solid point. I have a multi meter. What do I set it to again exactly and where should I connect it on the LED?

    I did try a fresh 9V and no change. Do I connect the battery in when I use the meter or take it out?

    October 31, 2021 at 3:18 pm #186181
    j_flanders
    Participant

    Connect the battery.
    Insert a guitar cable in the input of the pedal.
    Make sure the pedal is not in bypass mode.
    Set the multimeter to DC (somewhere in the 0 – 20 V range). The symbol is as straight line with a dashed line beneath it.
    Put the black probe on a ground point. Sleeve of the jack for example or any non painted spot on the enclosure.
    Put the red probe on either leg of the LED. One leg should read 0V, the other 9V (more or less).

    Since the LED doesn’t light up, most probable both legs will read 0V.
    Work your way back and find where the 9V connection to the board is interrupted.

    • This reply was modified 3 years ago by j_flanders.
    October 31, 2021 at 3:24 pm #186183
    j_flanders
    Participant

    You can use this wiring diagram.
    http://www.kitrae.net/music/Images_Secret_Music_Page/V8_Wiring_Diagram.pdf
    As far as I can tell it’s correct.
    It is not the one for the true bypass version but for 99% it will be the same.
    It shows where on the board and its traces you should read 9V.

    October 31, 2021 at 3:26 pm #186184
    j_flanders
    Participant

    I posted a follow up but it does not show up. :s
    Maybe I cannot post twice in a row?
    Trying again:
    You can use this wiring diagram.
    http://www.kitrae.net/music/Images_Secret_Music_Page/V8_Wiring_Diagram.pdf
    As far as I can tell it’s correct.
    It is not the one for the true bypass version but for 99% it will be the same.
    It shows where on the board and its traces you should read 9V.

    October 31, 2021 at 3:29 pm #186185
    j_flanders
    Participant

    You can use this wiring diagram.
    h t t p s://tinyurl.com/44zv9unt (remove the spaces. This forum rejects my post if it contains certain urls. The url leads to Kitrae’s site with a pdf of the V8 wiring diagram)
    As far as I can tell it’s correct.
    It is not the one for the true bypass version but for 99% it will be the same.
    It shows where on the board and its traces you should read 9V.

    • This reply was modified 3 years ago by j_flanders.
    October 31, 2021 at 8:59 pm #186187
    Minor_Issue
    Participant

    Thank you this is extremely helpful. I am poking around with the multimeter trying to figure out the problem. Good news, our LED is back on. I plugged the pedal in again and while I’m no longer getting any bypass signal, with the effect on I’m getting some distorted sounds, something between ring mod and octave fuzz.

    I was able to ascertain that the pots do seem to be functioning correctly. I can turn them up or down for volume, sustain, and tone and they all work even in the warped distorted state. I also noticed if I stick my finger on the output jack the signal comes through much clearer. Still no sound when the circuit is off.

    I’m set to DC on my multimeter but I’m not getting your 9v reading at the LED even though now it’s on. Maybe I’m just dumb. EDIT: I’m getting 1.6V and 0 at the LED

    Still poking away at it!

    October 31, 2021 at 9:13 pm #186189
    Minor_Issue
    Participant

    9.3V definitely passing through the circuit along the yellow line of the circuit in the diagram. LED shut off now even when circuit on, after reading 1.65 for a while.

    November 1, 2021 at 5:49 am #186190
    j_flanders
    Participant

    1.6V instead of 9V on the LED is fine. I see the current limiting resistor is before the LED, so 1,65V is the voltage from the LED.
    Do you have any idea on what could have happened in the mean time? You’re now experiencing the opposite: it works in effect-mode but not in bypass-mode, while originally you had bypass-mode but no effect-mode. How can the LED suddenly start to light up?
    You’re not by accident plugging your guitar into the output of the the pedal? (Given that it has its input at the left and the output at the right, whereas on most pedals it’s the other way around;)

    November 11, 2021 at 8:59 pm #186211
    Minor_Issue
    Participant

    Ok, I’m back, sorry real life got in the way of guitar pedals (very sad).

    So I did some rewiring, there were some loose connections. Good news and bad news: good news is I’m getting 9v almost everywhere, now. Bad news is that I also seem to be getting 9v now through the ground section. I’m 9v on either side of the LED. 9 volts anywhere on the hot loop and the ground loop. Pedal is obviously not turning on.

    Is there some way I accidentally wired it to itself or something funky going on?

    Much appreciate you, sirs.

    November 11, 2021 at 9:22 pm #186212
    Minor_Issue
    Participant

    Realized I was measuring wrong. Getting some normal readings now. LED still not turning on. Voltage readings now in line with 9v at one end of LED and 0 at the other

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