MXR Carbon Copy: no signal in wet mode

[fga]

Hello!

My MXR Carbon Copy (guitar analog delay effect) does not generate any output, if effect is switched on.
In bypass-mode it gives a signal.

I had a look inside, but nothing obvious to me was visible.
Then I tried to measure all capacitators, nothing seems wrong with that.

I am no technical expert: could you help me to find out, what else
could be wrong?

Are there schematics avalaible?

Are there typical errors with this box or type of effects?

This is my first try to repair such a box so please forgive me
the many and very basic questions.

Thanks for your advice and help!

[52 Bill]

Welcome to the place.

My MXR Carbon Copy (guitar analog delay effect) does not generate any output, if effect is switched on.
In bypass-mode it gives a signal.

A fairly common problem with these is that the switching fet transistors will short and stop the signal from getting through.

Unfortunately the fets are surface mount parts and are difficult for a beginner to replace. What sort of experience do you have in repairing electronics?

[fga]

Not much.
I now, how to solder, and how to use a digital multimeter,
as well as a meter for capacity. I would be able
to find out (with help of the multimeter), if the switch knob is damaged,
if I would could take a look at the schematics (I can't, I don't have it).
And I now basically, what a fet does and do understand, that they
are difficult to replace (I do not know, how to find out,
which of the 19 fets could be faulty).

Should I measure the resistance of the (two) visible pins?

[52 Bill]

(I do not know, how to find out,
which of the 19 fets could be faulty).

A quick internet search tells me that the 4 fets that control the switching are Q10, Q11, Q12 and Q13. Dunlop suggests replacing these with J176 or J177 fets.

[fga]

A quick internet search tells me that the 4 fets that control the switching are Q10, Q11, Q12 and Q13. Dunlop suggests replacing these with J176 or J177 fets.

I will try this.

How can I change them? They have little black sockets.
And no solder-joints (is this the correct english word??? sorry...)
are visible from the other side of the circuit board.
Do you know the name of the original fets?

[52 Bill]

How can I change them? They have little black sockets.
And no solder-joints (is this the correct english word??? sorry...)
are visible from the other side of the circuit board.

These are surface mount components. They do not have wire leads that insert through the circuit board. This is part of the reason that they are so difficult to repair without the correct tools and experience.

Each fet is a small rectangular black plastic block that is about 2mm x 5mm. There are three solder points, two on one side and one on the other. All three solder points must be melted at the same time in order to remove the part.

If you have a soldering iron with a small enough tip, then I would suggest that you purchase a small package of ChipQwik to help you to remove the parts without damaging the pc board. You might also try looking for videos that instruct how to remove surface mount components before you start to see if you feel confident in trying this repair.

As for the original part numbers, I assume that they are J177s. Look at the ones mounted in your pedal. What number is printed on them?

[fga]

Sorry, it took some more time to answer this question,
cause I first of all had to buy a better loupe to find this out.
Q11-Q13: 6Y F
the F is rotated 90° counterclockwise
Q14: IR4
(or maybe also: 1R4).

I tried to find a distributor (in Germany) for J177,
but could not find one on first attempt.
Maybe I can find another designation.