Mu-Tron Octave Divider

[Jargo]

Ok Folks, here's a good one!! I received this from a friend down south and he received this unit from an old friend who died. Basically, to say that it wasn't in good shape would be an understatement. I've done a ridiculous amount of research on this box and can only come up with the wrong-year schematic, which shows most of the components in the wrong places. At any rate...I decided to go gently and first just replace old wires and re-flow some of the old solder. I discovered that someone had stepped on one of the knobs thinking it was a footswitch and broke the Pot's traces off the PCB, taking with it a few other things. I fixed those very carefully!! Now I have everything flowing and though the pedal works, there's a few things!

The pedal does seem to Bypass normally and the power button seems to work (but LED does not light up)

1-  The LED's don't work...the owner does not remember if they ever did. I did not want to risk taking them out if something else is responsible for this.
2-  The effect switches On and OFF  -  a very subtle octave-up and octave-down sort of thing with Fuzz. Consistent with switching the RINGER on manually.
3-  The MIX pot doesn't seem to do anything.
4-  Upon stepping on the BASS ONLY switch, the fuzz goes away almost completely and the remainder is almost at regular bypass volume.

The STABILIZE button seems to do nothing as stated by many users.

I will put up some PIX in the next few days.


Any help would be appreciated!!!!

[theehman]

I've fixed a few of these before.  Test the LEDS first and make sure they're good.  They're not just there for decoration. 

[Jargo]

Hi Ron,
Thanks for the advise, I will test and/or replace the LED's.  Any Ideas as to why the effect isn't less distorted and with clearer up/down octave sound??

Thanks, please be patient....I'm fairly new at this.

[SonicVI]

Ok Folks, here's a good one!! I received this from a friend down south and he received this unit from an old friend who died. Basically, to say that it wasn't in good shape would be an understatement. I've done a ridiculous amount of research on this box and can only come up with the wrong-year schematic, which shows most of the components in the wrong places. At any rate...I decided to go gently and first just replace old wires and re-flow some of the old solder. I discovered that someone had stepped on one of the knobs thinking it was a footswitch and broke the Pot's traces off the PCB, taking with it a few other things. I fixed those very carefully!! Now I have everything flowing and though the pedal works, there's a few things!

The pedal does seem to Bypass normally and the power button seems to work (but LED does not light up)

1-  The LED's don't work...the owner does not remember if they ever did. I did not want to risk taking them out if something else is responsible for this.
2-  The effect switches On and OFF  -  a very subtle octave-up and octave-down sort of thing with Fuzz. Consistent with switching the RINGER on manually.
3-  The MIX pot doesn't seem to do anything.
4-  Upon stepping on the BASS ONLY switch, the fuzz goes away almost completely and the remainder is almost at regular bypass volume.

I repaired one recently myself with non-working LED's.  If I recall correctly the LED's are all connected and if one goes out then the other two won't work whether they are good or bad.  Might as well just replace them if you're gonna go through the trouble of taking tem out to test them.    Mine also had the same problem with the mix pot. It turned out to be a bad opamp on the logic board (the one with the CMOS chips on it).   Best bet to to use an audio probe on it.

[SonicVI]

Oh, and the stabilize switch DOES do something, it's just subtle.  It greatly reduces octave skipping on the lowest 6 frets or so, above that and it's not really noticeable. 

[Jargo]

Thank you so much! I will check with the probe next, and yes, you're quite right; one of the LED's was bad, the other two were fine. but I went for new ones and they're looking great.
Again,  thank you!!!

[Jargo]

Do you happen to recall what kind of CMOS you used to replace the ones in your pedal. I found a number of 4013 CMOS Dual, Flip Flop at Mouser but I'm unsure which, if any are the differences.

Much appreciated!!

[SonicVI]

No, I don't remember which exact ones I've used, the CMOS chips were ok in my pedal. I think any CD4013 and CD4017 should work, and any 4558 compatible dual opamp.   Have you tried the audio probe or are you just going to just start replacing everything and hope it works?

[Jargo]

To be perfectly honest, I'm trying to not change any parts, as the unit is of great sentimental value to the owner, but I don't want to spend eternity trying to fix this piece either;  I'm doing it for free, I'm fairly new to this craft and that's why I described the issues and what they sounded (or not) like. You seem to be familiar with the issues, so changing the CMOS as you suggested seems like  the best thing I could probably do. I'll put in sockets for the chips and maybe replace all the 4558's (any one better than any other??).

Thanks you sooo much!!

[SonicVI]

No way of knowing what's wrong with it without having it in front of me to test out, could be lots of things.    You said that it does pass signal, the ringer works, but the suboctave doesn't work.  That most likely narrows it down to something on the logic board, could be an opamp, could be a CMOS chip, could be a transistor.   Do you have a copy of the schematic?  It's been posted in previous threads about this pedal if you do a search.  It will help greatly. 

[Jargo]

Thanks for bearing with me!  I have read most (if not all) of the thread in this site regarding this pedal and do have all (all the same) schematics for it (including the Service Manual)

The unit I have is slightly older (I think) and the location of the components does not match when compared to what I have. In my unit, the much larger 470uF caps are placed at a 45 degree angle in the board, across the MIX pot on the board. Also, the logic board is hard-wired to the main board, not as in 'newer' units.

The pedal does pass signal bypassed and with the effect ON (using foot switch and flicking the button). The effect sounds Fuzzy but with a hint of octave-up and a hint of octave-down. No way to control the volume, though. Mix pot seems to not do much and the Tone pot just adds a bit of 'Air' if turned all the way clockwise.

Stepping on the BASS ONLY foot switch cleans up the Fuzz and makes the sound less loud.

Thank you!!!

Dennis

[theehman]

Check the solder joints on all the pots.  I run small wires from the pads up the side of the lugs and solder them to the lugs and pads for a better connection.  The lugs on the pots are just barely long enough to make it through the circuit board to the solder pads.  I've seen a lot of poor connections there.
Audio probe both sides of the Mix control for clean and effect signal.  Make sure you do the connection fix I just mentioned first!

[Jargo]

Ron,
Thanks!  I thought about that since the pots did come loose a few times while trying to put the guts back in....very unnerving, specially since I was already in the 'I'm done' mood!

I may very well get them pot out of the board and on their own, I'm sure it will make a difference..Again..thank you!

Dennis

[theehman]

I wouldn't remove them.  Remove all the solder from the pads then put a wire (resistor lead is what I use) in the hole.  Put a small bend in the end of the wire so it lays on the pad.  Solder it down to the pad and solder should flow up the lug along the wire.

[Jargo]

Ooh, I see!!! Genius!!!

Thx!

[Jargo]

Also, do you happen to know the values on these pots??
One of them has a bent shaft which has to be turned carefully as to avoid breaking the solder joints.

[Jargo]

ALLRIGHT!!!!


IT'S ALIVE!!

-  I performed the POT surgery (extending POT leads using resistor legs) suggested and seems like it's what it needed.
-  The "bass Only" LED and foot switch work fine.
-  The Ringer switch engages the effect - fuzzy/ringy type of thing, cool!
-  The Stabilize switch seems to work - smooths out the tracking of the effect on the lower freqs - nice!
-  Pots sound like they're doing what they're supposed to do, mix & tone, but  I wish I could get them to turn easier.

    One thing though... I've also changed the "power" LED but now notice that the "effect" LED stays on regardless of the state of the pedal.

Any thoughts???

THANKS TO EVERYONE WHO HELPED ME INCH MY WAY TOWARDS GETTING THIS THING GOING AGAIN!!

Dennis

[Jargo]

It's all fixed up!!

Thanks go out to everyone.

Dennis.