I'm desperate for help wit troubleshooting a PT-80 Delay

[solderman]

Hi all

I'm desperate for help wit  troubleshooting a PT-80 Delay effect from generalguitargadgets.com I have emptyed out all my own ides how to get it to work. What I definitely know is:

- I'm 100% sure that there are no soldering bridges or bad solders or such errors.
- I'm 100% sure that all components are the right one on the right place and polarity /pinnout is double checked.
- The dry signal comes out nice an clean but the delaysignal is so week that it is hardly audible.
- I have back traced the circuitry with a signal feed to the effect and then taped the circuitry for signal trough a "cap on a cord" to an amp.
- I have a good delay sound on pin 14 on the PT2399 and the delay time pot works witch gets me to believe that its OK so far.
- There is a VERY faint signal on pin 6/7 on the SA571 witch leads me to belove that the problem is here. But I am not sure what this thing Reilly is soppose to do. I get a bit confused when I read the datasheet for the SA571 I don't understand how it suppose to work in conjunction with the PT2399.

I suspect that the SA571 is the problem but I only bought one from Smallbear so I can't test a different one.


Any suggestions, please how I should  proceed to be shore I have drawn the right conclusion or how to fix it???


Schematics

http://www.generalguitargadgets.com/diagrams/pt80schem.pdf

Thanks
//Solderman

[Auke Haarsma]

I happen to have a PT80 on my desk at the moment. If you could post some voltages I can compare.

Are you using the new version? (with the charge pump onboard)?

[solderman]

Hi
Yes The MAX 1044 is on board

Some readings SA 571

Pin 12= 1,77

Pin 13 11,87

Pin 14/15  strong sound 1,77 V 
pin 12 No sound 1,77V

Pin 2/3 week but delayed sound 1,77 V
pin 6/7 Very week sound 6,53 V

Pin 2 an3 3 on TL o72 No sound 5,92 V


Gratefol for help

//Solderman

[Auke Haarsma]

I have the 'old' PT80, so no MAX1044 on board. I do feed it with 18V DC, so the voltages should be the same.

Input voltage: 17,58V
Output of 78L12: 12.04V
Output of 78L05:  5.02V

Here are my voltages on the SA571
1: 0.95V
2: 1.84V
3: 1.84V
4: gnd
5: 1.84V
6: 3.36V
7: 3.36V
8: 1.84V
9: 1.84V
10: 5.78V
11: 1.84V
12: 1.84V
13: 12.03V
14: 1.84V
15: 1.84V
16: oscilliating between to 1.8V

The only difference I see is the voltage on pin 6/7. Mine is half yours.

Now back to what you wrote.

Good delay out of pin 14: that's good. The PT2399 is giving the delayed signal.
But, at pin 2/3 of the SA571 the signal is already weak. That means the signal gets weak even before going into the SA571.

What to do: Follow the signal from pin 14 of the PT2399 to the 2N5088. How is the signal at the base of the 5088? And at the Emittor?

[solderman]

Hi thanks a lot for the info. Auke
I'll dig in to this to night after work. I'll post the results later


//Solderman

[solderman]

Jippeii, It works

Thanks a mil Auke for the voltage readings. They got me on the right track. It was a cupper trace that touched a pad on the PCB, not a solder joint but it gave the same result. I etch all my PCB:s my self with the copper lami with fotoresist and UV light method. . When I print the transfer on a transparent paper it won´t get any better than the original. In this case that was not good enough. Sins the original picture resolution was bad. Se the pic. Below.




It has cost me 5 hours of trouble shooting but I learned not to trust the PCB and check this as with solder bridges. Now its sounds very nice. I haven't compared it to my Rebot delay 2.5 but Im going to an Im going to post sound clips of both on my site.
 

//Solderman

[Auke Haarsma]

glad I could be of help.

Have fun!