Half dead MXR EVH phase 90, help??

[DanD1985]

Hi folks, I was wondering if anyone has come across a problem in the MXR EVH phase 90 whereby the pedal will turn on and the LED will light but no effect is heard. It shuts the signal down completely and I just get a low level noise coming out my amp.

I had read on t'interweb that this may be to do with the Zener 15v diode having failed Diode CR1 IIRC on the supplied schematic but I'd rather ask some folk directly before I go about de-soldering components of the pedal.

Could the problem I describe be related to anything else?

Why would this happen? I use a t-rex fuel tank to supply 9V centre neg as shown on the pedal. I took the pedal cable out as i never use 9v blocks for pedals. If I can understand the source of the fault, I can try and make sure I don't do it again.

Is there anyone out there who has fixed one of these or its brother models with a fault similar to this?

Thanks and regards,

Dan.

[ICBM]

I can't read the schematic (too small resolution), but if the Zener is an overall reverse-polarity and voltage-protection diode, it isn't the cause of the problem because if it was shorted it would stop the LED from lighting as well.

It's more likely to be either a broken solder joint somewhere, or a failed IC.

[lasermonkey]

I think the Zener is a 5v1 and is used to bias the FETs. This is from memory. I can't read that schematic either, but I have built a few clones before.
But yeah, check for dry joints first of all.

[DanD1985]

I can't read the schematic (too small resolution), but if the Zener is an overall reverse-polarity and voltage-protection diode, it isn't the cause of the problem because if it was shorted it would stop the LED from lighting as well.

It's more likely to be either a broken solder joint somewhere, or a failed IC.

Thanks guys, I'd have seen this sooner but I forget to set so I get notifications

I'll have a bash at the dry joints first.

There are a number of test points on the board as well. If I take a multimeter to them and going tp1-tp2, tp2-tp3 etc help me locate the region of the fault. Presumably the test points allow for analysis of the section of circuit between the points?

Cheers again for your help guys.

EDIT: Here's a link to a bigger version of the schematic:
http://farm8.staticflickr.com/7051/6...a4148157_b.jpg