MXR Carbon Copy Repair

N

nate_noise

New member
Hi Folks,
Recently picked up a broken Carbon Copy for $20. Original owner says "all of a sudden one day, the output became extremely quiet."
I get a clean signal in bypass mode, but when the pedal is engaged it's extremely quiet but I am able to hear delays (if I crank my amp way up). With Regen cranked it won't self-oscillate though. (A hint as to where in the signal the gain drop is happening?) I've tried with both battery and adapter.

I've attached a photo of the PCB and also the only source I could find online claiming to be a Carbon Copy schematic (low res, kinda hard to read).
Any tips on troubleshooting what the problem might be? (I'm still a novice pedal builder.)

Thanks!

-Nathan
 

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Hey, havent had much time to dig in deep w mine. I tried reflowing the solder on a bunch of the larger connections, but it didn't help. I tried tweaking some of the trim pots but that didn't help either, and the guy who sold it to me told me it just stopped working one day without explanation (he had nothing to gain by lying about fiddling w the trim pots, so I certainly believe him).
I might order replacements for Q10-13 and try swapping those at some point. But realistically- I might just build a new delay from one of the PCBs here instead and just harvest parts from this pedal.
Keep me posted if you find a solution to your problem. Good luck!
 
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Here is a schematic and some good information about troubleshooting the Carbon Copy:

可燃ごみ箱 MXR M169 CARBON COPY ANALOG DELAY 修理・解析

自作エフェクターやギター改造等を紹介しています。※自作や改造は自己責任で行ってください！
drugscore.blog.fc2.com drugscore.blog.fc2.com

How to distinguish between MXR Carbon Copy versions 1 and 2 and the difference in sound
gear-otaku.blogspot.com

コラム：MXR Carbon Copy バージョン1・2の見分け方とサウンドの違い

2008年の発売以降、プロ・アマ問わず多くの愛用者がいるアナログディレイの名機 MXR Carbon Copy。そのカーボンコピーには、超初期モデルのバージョン1と発売直後にアップデートされたバージョン2の2種類が存在し、サウンドも異なります。見分け方は続きへどうぞ。
gear-otaku.blogspot.com gear-otaku.blogspot.com
 
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FYI - there are similar discussions on the Carbon Copy failures and possible repair guidance on the other forums, e.g.,
https://www.freestompboxes.org/viewtopic.php?t=6559 where they suggest replacing SMD JFET Q10, and provide photos of the board.
I can't say which repairs might work, however I also own a dead one that I barely used so it sure seems that MXR has a bad design failure here. I just haven't decided yet whether to try my luck replacing SMDs vs brutally torturing it...
 
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Hi, newbie here. Got a mini CC that died on me 2 months after the warranty expired. I hadn't touched the guitar or pedal board in a while, and when I finally did. the delay wasn't outputting any guitar signal, but rather a repeated disturbance. I've checked all the electrolytic capacitors, the SMD type, with my bench LCR meter. They all suck!!! Sub-par pieces of crap! Phase angle at around 60 degrees, capacitance way lower than a 20% tolerance calls for, not to mention varying high ESR. I've replaced them all, but that didn't fix the problem. I'm guessing these crap caps had taken out an IC upstream. This is extremely difficult to debug w/o schematics, but I've managed to verify the 4 coolaudio IC's are fine, and so is the SA571 compander. I've shorted one of the FET's (one of the Q10...13) with a small screw driver, and some analog signal became audible through my amp. Just ordered a bunch of MMBFJ177 (SMD FET), with the intention of replacing the suspects. This really sucks! I'm very disappointed with MXR, albeit I loved that carbon copy. Will keep updating.
 
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I had my CC repaired by MXR. It cost me $75 which is just short of buying a new one. I don’t know what the problem was (they wouldn’t tell me) but I also didn’t want to troubleshoot myself, so…
 
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Just to chime in, a common problem in amps that displays this same symptom is when the input/output jacks become corroded or just covered with muck. You might try cleaning them.
 
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Hello everyone, I just found out about this thread because I have a problem with my carbon copy pedal since there are no repeats (the REGEN control does not work).

Any suggestions on the possible error?

greetings from Ecuador..
 
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Mine is broken too. Engaging the pedal increases the volume slightly but no delay. Messing up with the multimeter I managed to get some delay noises which leads me to think that the issue is within the bypass circuit

I found that the bypass uses some FETs and about the ESD issues being caused but had no success
My issue looks to be something like this; hope it might help others too.

Delay pedal Repair, MXR Carbon Copy Repair Newark - Ampworks

This MXR delay pedal repair, is one of many I've fixed so it was a nice quick job. I keep the repairparts in stock in my Newark (East midlands, UK) worshop.
www.ampworks.co.uk www.ampworks.co.uk
 
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Does anybody knows how could I bypass the bypass circuit? I mean, connecting the IN directly to the delay circuit itself? I took a look to the schematics as seem here https://drugscore.blog.fc2.com/blog-entry-324.html#gsc.tab=0 but couldn't figure it out on my own.

At least, that would make the pedal usable for recordings while I have the chance to verify if I'm right about the problem. Also builds me time until I have the chance to import the needed components.
 
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felipesareas said:
Does anybody knows how could I bypass the bypass circuit? I mean, connecting the IN directly to the delay circuit itself? I took a look to the schematics as seem here https://drugscore.blog.fc2.com/blog-entry-324.html#gsc.tab=0 but couldn't figure it out on my own.

At least, that would make the pedal usable for recordings while I have the chance to verify if I'm right about the problem. Also builds me time until I have the chance to import the needed components.
Click to expand...
There are a number of test points on the schematic. Those would be ideal points to test with an audio probe to see where things go sideways.
There's a fet buffer for bypass and a npn buffer before the first opamp on the top right of the schem.
Bypassing the in circuit but buffer won't fix it.
I would probe the test points, or the outputs of each gain stage.
If that seems too complicated, I would recommend not going further with any fix attempt, to be honest.
 
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