Broken Improved Hum-Free ABY - Help!

Started by zpyder, July 25, 2007, 09:03:28 PM

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zpyder

Hey guys, I posted a while back (http://www.diystompboxes.com/smfforum/index.php?topic=58567.0) that my hum free ABY wasn't working, then reposted that it was fixed as I opened it up, pulled out IC's, blew on them, and put them back in - resulting in a working pedal.  Wellllll... now it's not working again.  same symptoms.  Here's the lowdown, please help:

When my ABY is connected into the my pedal board's signal chain, I get NO output on either channel, whether in A mode, B mode, or Y mode.  Bypassing the ABY solves this (in other words the rest of the board works fine).  The LED lights DO turn on.  Occasionally when pressing one of the stomp switches to change channels, the ABY causes a short and since most of my pedal board runs off the same supply, I get an intermittent shut off of all pedals that last about 2 seconds until shit turns back on (ouch).

Details:

1.Name of the project: Improved Hum-Free ABY
2.layout: http://aronnelson.com/gallery/humfreeaby/Improved_Hum_Free_ABY_PCB
3.I perfboarded it... here is the best pic I have of it: http://aronnelson.com/gallery/zpyders-build-pics/Hum_Free_ABY_008
4. No parts substitutions
5. No regrounding ... this circuit uses a MAX1044 to get both +9v and -9v
6. This pedal is intended to split my guitar signal into two signals with the same output.  I can either select one or the other output, or both, via stomp switches.  It include two 42TM018 xformers to isolate the different outputs, thus preventing any grounding issues with the two separate chains/amps that the two outs go to.
7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? => I'm using an adapter than reads 14.73 volts
Now insert the battery into the clip. If your effect is wired so that a plug must be in the input or output jack to turn the battery power on, insert one end of a cord into that jack. Connect the negative/black meter lead to signal ground by clipping the negative/black lead to the outer sleeve of the input or output jack, whichever does not have a plug in it. With the negative lead on signal ground, measure the following:
Voltage at the circuit board end of the red battery lead = +12.0v
Voltage at the circuit board end of the black battery lead = 0v

Now, using the original schematic as a reference for which part is which (that is, which transistor is Q1, Q2, etc. and which IC is IC1, IC2, C1, and so on) measure and list the voltage on each pin of every transistor and IC. Just keep the black lead on ground, and touch the pointed end of the red probe to each one in turn. Report the voltages as follows:

IC1: TL071 #1
P1: 7.68
P2: 7.85
P3: 1.37
P4: .71
P5: .24
P6: 7.95
P7: 7.97
P8: 12.08

IC1: TL071 #2
P1: 1.1
P2: 1.1
P3: .2
P4: .71
P5: 0
P6: 1.27
P7: 1.27
P8: 12.1

IC1: MAX1044
P1: 12.11
P2: 11.22
P3: 0
P4: .77
P5: .7 (!? - should be ~-12v)
P6: 9.97
P7: 9.2
P8: 12.1



The most obvious thing to me here is that my MAX1044 is not outputing a proper negative voltage.  Pin 5 should be the negative output of the MAX1044, but I'm instead getting a slight positive voltage.  Also the #2 TL071 seems to be behaving oddly...  I see problems but don't know what to make of them.  What's going on?

thanks!!!!
zpyder
www.mattrabe.com/ultraterrestrial Ultraterrestrial - Just doing our little part to make new rock go where it should have gone in the late-90's, instead of the bullshit you hear on the radio today.

zpyder

Also, it may be of note that both C3 and C8 are showing 0 at anode and .71 at cathode, though I believe this to be a result of the MAX1044's improper outputs.  Will it be of concern once I get this thing working again that some juice has been applied in the wrong way over these things?

thanks again,
zpyder
www.mattrabe.com/ultraterrestrial Ultraterrestrial - Just doing our little part to make new rock go where it should have gone in the late-90's, instead of the bullshit you hear on the radio today.

zpyder

www.mattrabe.com/ultraterrestrial Ultraterrestrial - Just doing our little part to make new rock go where it should have gone in the late-90's, instead of the bullshit you hear on the radio today.