Mangler issues in testing

[catfud]

This isn't my first build, but while the previous one went swimmingly (rangemaster) the mangler is causing more issues, meaning I'm having to seek the collected wisdom here... thanks for reading...

Project Name: Mangler

General Description of the problem:

No signal being passed through the circuit apparently, and odd biasing readings

Steps I've already taken:

The first thing I tried was to bias the board - my multimeter on the test point shows about 9v which isn't right...
Checked wiring, part values, and orientation (although the positive ground is a tad confusing I think orientation is ok)
Checked my soldering (no bridges or problem joints s far as I can tell)
Tried putting several different pairs of transistors in the sockets, same results
Tested continuity with a multimeter as far as possible using the schematic, no problems there
Done as much testing of on-board components as possible considering they're soldered in place (though my crappy DMM doesn't stretch to capacitor testing)
Replaced all caps and the diode
Tested the test rig, in case that's a problem, using another positive ground effect (rangemaster), and that's working ok.
Tried playing the guitar with everything connected - direct from guitar to amp works fine but no signal with the effect in-between.
Tested Battery (which is fine)

Any substitutions:

None, all component values are as listed in the Mangler PDF

Voltage readings:

    Q1    Q2
E   0     0.01 
B   0.16  0.01
C   0.01  8.98

The 20k trimpot doesn't reduce the voltage much to Q2, I think I'd need a higher value pot for that if there's not some other problem. But I'm guessing the real problem is elsewhere, and with luck not between the keyboard and the chair.

Does anything leap out as being an obvious problem to anyone? I keep coming back to it and drawing a blank - I just can't see what the problem is. Any pointers from you more experienced folks would be much appreciated. I've included some links to pics of the board.

[midwayfair]

Try flipping your transistors and report back.

[catfud]

Try flipping your transistors and report back.

Thanks for your reply, I tried flipping them and I get pretty much the same readings from Q1 and Q2. I'm not sure what to make of that though, as I thought a transistor had only one proper orientation.

[midwayfair]

Verify that your trimpot is actually working ... measure the ohms across the two lugs that aren't connected. This would be a weird case, but hey, weird things happen. Use the continuity setting on your multimeter (beep) and follow the circuit for the power and ground connections. Make sure everything's actually connected -- and also make sure nothing's connected that shouldn't be. Your eyes can lie to you.

[catfud]

Verify that your trimpot is actually working ... measure the ohms across the two lugs that aren't connected. This would be a weird case, but hey, weird things happen. Use the continuity setting on your multimeter (beep) and follow the circuit for the power and ground connections. Make sure everything's actually connected -- and also make sure nothing's connected that shouldn't be. Your eyes can lie to you.

Thanks Jon, I checked the trimpot, and it checked out ok-ish, it's measuring below the advertised 20k (circa 16.8k) when at its max resistance, but with its 10% tolerance and my general mistrust of my DMM's accuracy it probably scrapes a pass. I rechecked continuity and that seems fine.

Following up on the power/ground suggestion I took another look at my (battery only) test 'rig':



Having read the very helpful 'basic testing rig' post pinned at the top of this Tech Help section I put the makeshift one aside, and made a wallwart-driven test rig with an enclosure I hadn't drilled right and a Road Rage board that I had ordered at the same time as the Mangler, to see what improvement a proper +ve ground with -9v supply would make:



Using that I found I got much better results with the Mangler (I could hear some low signal and some fuzz, but still had the biasing problems. I wasn't sure about the transistors I had swapped in as an earlier test (and forgotten to swap out afterwards) so I put back the transistors that I had originally intended to use, that were within the right hfe ranges, retested, and woohoo! it sounded right! I could then bias the voltage to 4.5v - it's sounding great now, like a fuzz should   

I'm still not sure why the rangemaster board tested and worked fine with my original makeshift battery-driven test rig, and the mangler wouldn't, but it could be that there were multiple issues at play with the mangler. In any case, really pleased now that it's working, very many thanks for your helpful suggestions!

Now to figure out how to properly finish an enclosure...

[midwayfair]

Glad you got it working