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 QuadraFuzz Troubleshooting 
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Joined: Fri Jan 27, 2012 8:48 am
Posts: 5
Post QuadraFuzz Troubleshooting
Hi, Sorry if this is the wrong avenue to post my issue, but I wasn't really sure where else to submit this problem.

After assembling my quadrafuzz kit c/w 12VAC transformer, I've found that upon power up their is a loud low frequency hum coming from the unit regardless of whether it engaged or operating in by pass mode. No instrument signal gets through at all. I'm fairly confident that connections are correct and their are no shorts evident via test by multimeter or inspection.

I am wondering if my next step should be to replace the cmos switching chip to see if i've accidentally discharged some static into it. I am noticing that the output from the filter caps is about +/- 3.8VDC where it should be more like +/- 5VDC, so I'm not sure if this is an overload condition or a power supply issue.

I've bridged GS and G with jumper as indicated in the manual and the output from the 12VAC transformer is within tolerance.

Any tips from the guru's would be greatly appreciated on this one. As well as tips on handling CMOS chips during installation process.

Thanks,
Dave


Tue Jan 31, 2012 3:21 pm
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Joined: Sun Nov 09, 2008 2:49 pm
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Post Re: QuadraFuzz Troubleshooting
Hello Dave.

It's OK posting here, or, email direct to scott@paia.com.

As long as you were careful with the CMOS IC it is likely not the trouble. Usually it is just an accidental short-circuit to it or reaching down to touch it and a spark from static discharge passing through it that would take it out.

There are some extras including trouble-shooting tips and suggestions over in this section of PAiA Talk:

viewforum.php?f=23

But also, check to be sure the four ICs 1-4 are in the proper spots with respect to 4016 and 4136, and, to polarity. Sometimes die flashing can be confused as indicator for pin 1, but in almost all instances, the markings across the part will be lengthwise between the rows of pins and when the board is positioned for reading left to right, pin 1 will be the leftmost on the lower row of pins. For the two Voltage Regulators, go back and check again to be sure the 7805 and 7905 parts are not in each others places.

If an IC is out of place or backwards, use a bulb or springloaded pump to vacuum melted solder from each pin so the part can be pryed off and re-installed or replaced.

Here's to success!

--Scott

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Scott Lee
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Wed Feb 01, 2012 11:23 am
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Joined: Fri Jan 27, 2012 8:48 am
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Post Re: QuadraFuzz Troubleshooting
Scott,
Thank you for the tips. I re-tested the v+/- on each of the ic's. I end up with +2.85v and -3.81v on the supply pins for each chip. I should also moention that with the unit on and no input or output connected d1 d7 d5 and d3 are faintly illuminated.

I will test the opamp outputs as well once ive tested them.

Do these symptoms indicate where the short or faulty component could be?

The only thing that comes to my mind as a next step is to dismantle the ps components and bread board them and test what the output is under no load.

Thanks in advance for any help you can give.

-Dave


Wed Feb 01, 2012 9:05 pm
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Joined: Fri Jan 27, 2012 8:48 am
Posts: 5
Post Re: QuadraFuzz Troubleshooting
The output from the op amp sections are between .2 and 2v


Wed Feb 01, 2012 9:09 pm
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Post Re: QuadraFuzz Troubleshooting
Since the power supply voltages to the ICs are low, there must be something wrong with them or a connection between them (solder bridge) or within one of the ICs. Do any of the four DIP ICs feel hot or warm?

Check again to be sure IC5 is the 7805 and IC6, the 7905. Oh, and in case we've overlooked the dc polarities (not looking at your reported readings right now), Diodes D10 and D11 must be installed with their banded ends matching the banded (bar) marking on the printed-circuit-board. The rectify the ac voltage from the transformer to the negative and positive dc voltages going into ICs 6 and 5.

It might be revealing to connect the Individual Outputs (Js 6, 7, 8, and 9) in turn to an amp/speaker and comparing any hiss/noise or guitar signal or lack thereof between each of them.

Sometimes a desoldering pump or bulb can clear melted solder from a joint enough that there is a space around it in the hole through the solder pad and doing this at the regulator output pins, then, on the other ICs in turn, will isolate things so you test voltages, narrowing down the possibilities (instead of taking things off the board and rebuilding them). It might be necessary to nudge the pin gently to bend it away from contact with the pad, centering it in its hole.

If you can email a not-so-lo res and in-focus image of the top and bottom sides of the board, I might be able to spot something and reply.\

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Scott Lee
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Thu Feb 02, 2012 2:02 pm
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Joined: Fri Jan 27, 2012 8:48 am
Posts: 5
Post Re: QuadraFuzz Troubleshooting
Scott,
Each output yeilds the same noise and no signal output.

I measured the signal pins on ic1b and found the following with a guitar plugged in to lo.
4: .7VDC
6: .5VDC
8: .69VDC

I will send photos of the board along later tonight. Thank you.

Dave


Fri Feb 03, 2012 5:57 pm
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Joined: Fri Jan 27, 2012 8:48 am
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Post Re: QuadraFuzz Troubleshooting
So I finally brought this one out of the box of unfinished projects and got it working :) It turns out, that the on board filter caps that were supplied were 10uF, so it was poor filtering causing the supply issues...I popped in some 470uF I had kicking around and it works as it should...

It's still pretty noisy though, so i think the next step will be to use some sheilded cable on the inputs and build an off board power supply to keep the AC out of the unit itself...

Then I just need to decide how i want to house it....It's my first piece of rack gear, so i am considering building a pedal board that houses it...but part of me want's to remove it from the faceplate and re-house it in a more pedal board friendly enclosure. I can probably do without the effects loop and individual filter outputs to save some real-estate as well.

Cheers! Dave


Sun Mar 12, 2017 10:55 am
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