my ibanez CP-9 passes effect but no dry signal....

[jerms]

hey newb here with a first post..... i have a well used CP-9 pedal that passes effected signal but no dry signal..... i'm assuming it's the flip flop network but have no idea how to suss this out..... i poked around a little but made no headway today..... are the 2SK445's the culprit??? i'm at a loss here and any help would be greatly appreciated... thanks in advance!

[armdnrdy]

If it's well used....poke around the tact switch. Do you have a meter?

Here's a link to the schematic:

http://www.cruachan-audio.pwp.blueyonder.co.uk/schems/Ibanez_CP9.gif

Also, look to the 2SK44 behind U1 for the bypass JFET.

[PRR]

(Thanks, Larry.)

There's only a few parts in the UN-effected path.

LM13600 buffer, a cap, the FET.

See diagram below.



You already know the first '2458 buffer works, it is common to wet and dry.

Feed a signal in. Use a Signal Tracer to see if it appears at these points.

For this use, a sig-tracer can be a guitar cord with an end cut off, any capacitor similar to 0.05uFd at >25V, and a clip-lead. Cliplead from circuit to cap, cap to cord, cord to any handy guitar amp, low-medium volume.

If signal gets to the 100nFd cap and FET, but does not come out the other end of the FET (both ways of the Effect switch/LED), then use a DC meter. First check for 4.5V at both ends of FET, then for 3V-6V at LM13600 pins 7 and 8 (expect 1.1V difference). Then probe the ByPass control path, 1Meg resistor, diode. In Bypass the resistor must be over +8V both ends. You can't really measure the diode to FET Gate path because both will be high-high-impedance. Tack-solder about 10K across the diode. If that makes it pass signal, the FET is OK and the diode is bad. (With the diode shunted this way, loud notes may distort, so replace the diode and remove the shunt resistor.) If FET still won't pass signal, shunt your 10K across the FET Source-Drain, that should pass signal. If all else is OK, replace FET.

Diode can be almost anything. For hasty repair, FET can be nearly any N-type JFET. For a factory-perfect repair you should find a FET of a very similar type; I think that number is available from pedal supply dealers (check SmallBear).

If signal won't get through the LM13600 dry-side.... that would be super-odd. You have to wonder why one side is sick and the other side is fine. However they didn't really need to use that extra buffer. Scratch-cut the traces to '13600 pins 7 and 8. Jumper the non-chip ends of the traces together so signal flows from input buffer to cap and FET. There's already two buffers (input and output); I don't see why they thought they needed two more (the 2-Q buffer inside '13600).

[armdnrdy]

Great instructions Paul!

I can almost hear that clean signal already!

This kind of problem is kind of unusual.....Usually it's.....It only passes clean signal!!! No effect what so ever!!!

Here's a few links to help you find teh JFET if that's what it turns out to be.

http://ceitron.com/shop/advanced_search_result.php?keywords=2sk44&search_in_description=1&osCsid=276a2fb194f26fa8203f67afd3707ac5&x=6&y=6

http://www.hbelects.com/Semiconductor/2S/2SK/FET-Semiconductor-2SK44-2SK44

There will be minimums and shipping so shop around and find some things you might need for future builds.

[jerms]

hey guys, thanks so so much!!!..... success!!!!...... it had no signal thru the jfet... so i went to tack on a 10K across the diode, per your suggestion, and right as i touched the iron to one end, bang there was the dry signal!!! so i reflowed both ends of that diode and she's back in action!...... this is my fave compressor.... i have two of them just in case of a breakdown, but this one sounds much better for some reason..... the cool ones a black label and the other is a silver label, not sure if that's why but......  anyway thanks again to both of you!!!

[armdnrdy]

Good news!!

All thanks go to Paul!!

[jerms]

you get props too man! i needed that schematic!!!