PT 80 Problems

[Ponchus]

Hi there
I've just finished putting together a PT 80, but I'm not having much success with it. I'm getting signal when bypassed, but nothing when engaged. I've tried audio probing it, but Im not sure where signal is supposed to be heard. I'm able to follow the signal at the input, and through the .047uf cap. The signal then "splits"- one direction goes into pin 5 of the TL072 chip, and the other direction goes into a 1M resistor. I hear the signal at the resistor "input", but not on its "output". I also hear the signal at pin 5 of the TL072, but not at any of the other pins.

The voltage readings from the TL072 chip are as follows. Also, from someone else's post, I've read that pins 1,2,3,5,6,7 should be 6v
1   1.46 (should be 6)
2   6.36 (should be 6)
3   6.03 (should be 6)
4   0
5   5.5 (should be 6)
6   1.5 (should be 6)
7   11.27 (should be 6)
8   12

Any ideas what I should look for as the culprit here?

[RDV]

Direction of opamp?

RDV

[Ponchus]

no, I'm definitely following the layout at General Guitar Gadgets...

[geertjacobs]

Are your 7812 and 7805 still putting out the right voltages?
They may have been damaged during soldering.

[RDV]

If you're 100% sure of your values and orientation of your parts, you should perhaps get a magnifying glass and check for any defects or solder bridges in your PCB.

RDV

[Ponchus]

yeah, i was kinda burnt last night, I'm going to go over everything again. The 12 and 5 volt regulators are putting out correct voltages (5 and 12 volts) so  i doubt they're at fault. The Vref line looks good too, I think...

[Roobin]

This happened to me as well (but not on a PT 80 admittedly).

Check ALL of the solder joints. Print out a copy of the layout/schem and go over each joint with a continuity check on a DDM if you have one + magnifying glass. Once you are sure its 100% good, highlight/cross off on the layout. This may be slow, but it will solve all solder problems.

Also check wires on pots/board connection are not hanging by a thread or strand, or even broken completely.

Also check pots. Use an ohmmeter setting on a DDM to make sure resistance is between 0 and whatever it should be. If it is off the scale or doesnt read properly, then it is probably broken.

Good luck

[Ponchus]

SUCCESS!!!! 

I started touching up all the solder joints when I came across a bad trace on the PCB (hey, this was my first etch job). I wasn't getting a continuity signal from my DMM across this one trace, so I soldered a lead across the trace (an excess piece of lead, cut off from a component at one point or another)...I then tested the pedal and immediately got sweet, sweet echo, echo, echo...awesome!

This has been a good week for me. I've gotten 2 projects troubleshooted (troubleshot?) with help from this forum. Thank you guys so much. I just started with this whole DIY building pedals thing. I ordered parts for my first two projects, a Tube Screamer and this PT80. But I probably made a major mistake in that I did both of them at the same time. Well, first I etched the boards for both projects together (just seems to make most sense) and drilled the PCBs and all that. Then I started on the TS, but I had forgotten to buy one cap (well, really I accidentally got a "surface mount" one and had to order a normal one), and Radioshack didn't have it, so I got as far as I could before I had to put it down and wait for my Mouser order (15cent cap, plus $5 shipping, equals frustration). So while I waited, I started in on the PT80. Finished it, no echo. TS capacitor arrives. Put down PT80, work on TS. No distortion. Hit the DIYSTOMPBOXES.COM forums, and get all the help I need from knowledgable, cool dudes who are willing to help out for no personal gain (thanks a million!!). Finally, distortion arrives, pushing the tubes of my...errr...battery powered little Pignose amp. I start in on the PT80. Still no echo. Again, turn to you guys. My eyes are bloodshot and I'm high off solder fumes, but I'm determined. Like Rocky fighting the Russian dude. And finally, the payoff!!! Stick in there fellow newbies, it's worth it when it finally works. Thanks for all the help!

[Roobin]

So now they're both working, hows the PT? I'm thinking of building an echo pedal and came across this one. Does it give a lot of flexability? Also is it noisy or not?

Have fun playing around with it.

[Ponchus]

Roobin: I haven't really gotten to play with it yet. I tested it on a little battery powered, Pignose sized Fender amp. I heard echo, I played with self oscillation a bit, I then screamed in joy and ran around the house for a bit. But I was running it on 2 9v batteries. I need to buy an 18v adaptor. At this point, I'm in the process of putting it in an enclosure. When I get the adaptor (hopefully this week), I'll test it and repost.

[RDV]

http://www.musiciansfriend.com/srs7/g=home/search/detail/base_pid/333104/

About $18.00 with the shipping.

RDV