Phase 90 - Bypass OK, but no sound when effect on...

[seekup1982]

I just got a Block Logo MXR Phase 90 that I was susposed to add a small filter to get rid of noise.  I always plug them up before I mod them to see if they work.  And this one didn't.  The client tells me that he had it working last week (I believe him) but that he used a different +9V wall wart to power his board (using a Boss tuner and daisy chain).  Now, the signal bypasses just fine, but when I turn on the effect, there is no sound whatsoever.  Also the LED doesn't come on.  I metered the power out of my wall wart at 8.9v but when I put my DMM on metering the positive off the board (connected) it showed .24v.  I did have to cable ends plugged into the in/out to let the no connects to be triggered so that it should come on.  I don't think the power is susposed to sag that much, even if it is still connected.  Shouldn't I be metering something higher?  He bought it used and I can see that the 4 phasing transistors were replaced and R22 was replaced with a 2.2M (instead of a 3.9M I think).  Does anyone know what might be causing this system not to work?  I don't have the pinout values yet, but still any help would be great.  How do I get the pinout values?  Just clip (-) to ground and touch (+) to the pins?  Thanks.

Ben

[petemoore]

yupp try touching R and B in Beep mode,,,you should hear a beep...
 Clip black to known ground, then check all grounds.
 Switch to 20v range on the meter, start at OA 1 Pin 1, write down the voltage and repeat for all the other opamp pins.
 Check out the debugging page, and: "What do I do when it doesn't work?' [a 'sticky' at top of forum listing]...try audio probing...I usually probe after I sort out the pin voltages...but I just use my 'thumbuzz Technique'...starting from output, working my way through the signal path toward input...you should hear a buzz sound when your thumb is connected to points in the signal path...if the noise is 'broken' at some point in the SP, that's where I'd look for a problem.
 You'll need to connect to a live amp and use a probe to connect your thumb to circuit points...but if you're reading a big voltage drop...you alluded to sag...I'd figure that out first using pin voltages as a guide.

[seekup1982]

What does "R and B" stand for?  Thanks for your whole post and tonight I'm going to find the pinout values.  

Ben

[petemoore]

Vague there...sorry
 The Red and black multimeter leads..

[seekup1982]

I just got an email from Dunlop's tech guy and he said that my friend probably used the wrong adapter (I didn't even tell him that!) and that I should replace the power diode (1N4148) and if that didn't work, replace the ICs.  He was very surprisingly helpful.  Anyway, I'll keep you updated.

Ben

[seekup1982]

Fixed it last night!  The problem was that he did use the wrong adapter.  The diode fried and luckily that was it.  I figured it out last night when I had hooked up a fresh 9.24v battery to it and after 10 minutes it got really hot and was only 7.81v.  Obviously it was like I was just shorting the battery.  Found out quick one 1N4148 diode was bad, put a 1N914 in its place.  Is this the right replacement?  Or should I use a 1N4001?

[MartyMart]

1N4001's are more commonly used as "power protection" diodes, it will "protect" a bit more than a 1N914 ! ( which conversely will "blow" easier )
Cheers,
Marty.