Help repairing old CMI Fuzz box?

crutter · June 18, 2021, 11:27:17 AM

Hello Everyone - I'm not sure if this is the right place to post but I thought, with the depth of knowledge here, that I might be able to get some help with resurrecting an old CMI Fuzz pedal I have been bequeathed.
Everything seems untouched inside the box but the black lead from the battery has come detached from wherever it is supposed to be. I've looked at a number of pics of old circuit boards and fuzz pedals but can't see anything that would correspond to this one for sure. I believe the black lead may go either to the circuit board somewhere or to one of the terminals in the on/off button?
Hopefully the pics will help.
Thanks in advance .
Chris

duck_arse · June 18, 2021, 11:37:34 AM

hello and welcome. that's some box.

can we have another photo or two showing the other side of the footswitch, and that obscured corner of the circuit board? can you read the part number on the transistors, and do you have a multimeter?

Sparky · June 18, 2021, 11:40:22 AM

It would be soldered to ground.

idy · June 18, 2021, 11:49:21 AM

Since the red battery lead goes to the output jack (ring?) this is probably a positive ground circuit...
That means the black wire goes to the circuit power. Will require tracing/schematic...

Mark Hammer · June 18, 2021, 11:51:10 AM

Looks VERY Fuzz Face-based.

Marcos - Munky · June 18, 2021, 12:34:28 PM

First of all, welcome.

As pointed out by Idy, it's a positive ground circuit, so the black lead is actually connected to circuit power. I agree with Mark it looks very FF based, or maybe Tone Bender based. More photos of the board will help us to identify the circuit.

Btw, also take some photos of that switch wiring. It seems too strange imo.

crutter · June 18, 2021, 01:57:35 PM

Wow, you guys are fast! Thanks for the replies.
Here are some more pics which I hope help. I managed to get one of the other side of the circuit board.
I do have a multimeter but I have little experience of working with circuits, etc. I can solder ok.
Let me know if there is anything specific you need to see more clearly.

Sparky · June 18, 2021, 03:07:33 PM

Oh,,,,, the red lead is going to the ground. Nevermind!

duck_arse · June 19, 2021, 10:51:35 AM

does that transistor say 2N4061? that would be pnp, and END BASE case. also, W.E.3. - would that be a wem/pep board, possibly?

http://pdf.datasheetcatalog.com/datasheets/newjerseysemiconductor/2N4058-2N4062.pdf

Mark Hammer · June 19, 2021, 12:22:15 PM

effectsdatabase says that CMI was owned by Marshall. Check here http://www.effectsdatabase.com/model/cmi and you'll see that the logo is the same as on Crutter's pedal. The site does not show Crutter's fuzz, only a later 3-knob model. But given the industry connection, is it possible the CMI was some sort of silicon Tone Bender Mk 1.5?

crutter · June 19, 2021, 12:43:52 PM

Thanks - yes, the transistors do say 2N4061, D_A. Well spotted.

The box looks a bit like an early Tone Bender or a Zonk machine. Although laid out differently, I think the components on the circuit look a bit like a Tone Bender, too, although I know nothing about circuits!

Yes, thanks Mark Hammer - CMI were a Marshall owned company set up to get round a restrictive deal they had done with distributer Rose-Morris - I had one of their guitars a long time ago. Some of the stuff was quite good although it wasn't regarded as top quality back in the day.

Thanks for all your help. If you have any clues about where the Black wire goes that would be great!
Chris

Sparky · June 19, 2021, 01:00:15 PM

How about doing a continuity check on all available components to see what's soldered to what ? [Looks Fuzz Face - ish or Tonebender to me, too. ] Finding the right connection for that battery wire should be pretty easy [?] Since I am of the "try anything to see what works" type, I'd put a battery in in and start touching that black wire to the circuit board! Cool pics, too! Thanx!

idy · June 19, 2021, 02:42:37 PM

So those transistor should be ECB. Power (black wire) goes through resistors to the Cs. Most fuzzes or even most amplifier type circuits this is true.

You figure which legs are C. The middle ones. What they are attached to. Is there a spot on the board that feeds the far end of those two Rs? You could read us the color bands ( hard, I know) and we could better fit to a known circuit... Or do like Sparky says. Like I guy they call Sparky would do...

crutter · June 19, 2021, 03:39:12 PM

Thanks for your advice Sparky and Idy. I'll try those ideas out.

Sparky · June 19, 2021, 05:51:22 PM

The worst that could happen is ......nothing........... and the best is the pedal could work! Either way we learn something.

crutter · June 20, 2021, 10:07:27 AM

Well, I soldered the black battery wire to the orange capacitor as Electric Warrior suggested (thanks EW). You could see some old solder from the previous connection. I put in a battery in and it works!
Sounds quite 'rough and ready' and the Fuzz knob doesn't seem to do a lot, although the volume knob changes the nature of the sound quite a lot.
I've been looking at a few circuits on the internet and it seems to resemble the Zonk 2 with the same type of 2n4061 transistors and layout. I wonder if whoever made those made some for CMI as well? What do you think?
Thanks again to you all.

Sparky · June 20, 2021, 10:46:05 AM

Quote from: crutter on June 20, 2021, 10:07:27 AM
Well, I soldered the black battery wire to the orange capacitor as Electric Warrior suggested (thanks EW). You could see some old solder from the previous connection. I put in a battery in and it works!
Sounds quite 'rough and ready' and the Fuzz knob doesn't seem to do a lot, although the volume knob changes the nature of the sound quite a lot.
I've been looking at a few circuits on the internet and it seems to resemble the Zonk 2 with the same type of 2n4061 transistors and layout. I wonder if whoever made those made some for CMI as well? What do you think?
Thanks again to you all.

Glad it worked! Of course you can't be positive the wire went to exactly the original spot and that "correct" voltage is reaching the transistors but it's a good start! I guess more will be revealed.

Marcos - Munky · June 21, 2021, 09:28:08 AM

Nice to know it's working.

Btw, how's the noise when it is bypassed? With yout photos, I figured out this weird switch wiring, and the output of the fuzz is always connected to the output jack. The switch just connects the input jack to output jack or fuzz input. So, since you have the output of the fuzz always connected to the output jack, if the circuit gets some noise, you'll always hear the noises even when it's bypassed.

Since it already have a dpdt switch, you can easily fix this by connect the wires the correct way, and still keep the original switch.

Edited: on your fuzz pot almost doing nothing. Correct me if I wrong, but that 4k7 resistor wired in parallel with the pot seems to be the cause. Try to lift one of it's legs and check if the fuzz pot acts better.

Marcos - Munky · June 21, 2021, 10:00:53 AM

I did a quick trace of the circuit, and this is what I got. Not sure if it's correct, and not really sure on that 68K resistor. Could you check this resistor, and also the missing values?

anotherjim · June 21, 2021, 10:25:19 AM

How do you switch the battery off? Doesn't seem to be a TRS input jack.

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Help repairing old CMI Fuzz box?