PT2399 based Faux echo delay chip won't start up.

[TK2]

HI,, wondering if there is anyone here that has built the Wampler Faux Echo/Delay Circuit.. I've finished the board a couple of days ago and have been feverishly trying to get the circuit to work... The TL-072 chip is amplifying Signal in,, Signal out but there is absolutely no effect PT2399 chip wise..
Any one else have this problem.. ? Thank you.

[patrick398]

Welcome 

A link to schematic, and pictures of both sides of the boards will help. Voltage readings on IC and transistor pins are also useful. Have a read of the debugging guide: https://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[anotherjim]

+1
We have to know what layout you built it to. Usual error is the orientation of the 5v regulator which is backwards about between 7805 or 78L05 versions.

[TK2]

Hi the board was made from this Schematic.

[TK2]

http://guitar-fx-layouts.42897.x6.nabble.com/Wampler-Faux-Tape-Echo-td36083.html Hi here is the link to a schematic that is very close.. This forum won't let me post the original schematic..

So,, 2 problems.. No signal to the Volume control and no signal going to pin 16 input on the 2399.. Also  the signal won't pass through the 511 k resistor but there is audio output at Pin 7 of the 072.

There is some type of output(Wave form) at pins 9 10 12 14 and 15 of the 2399. Not sure if those are the Modulation signals or actual input from the 072,

The Dc pin voltages on the 2399 are
1-5.08vdc
2-2.54
3-0
4-0
5-2.93
6-2.54
7-.28
8-0

9-16 are2.54 vdc  on all pins

tl072 vdc

1-4.74 vdc
2-4.34
3-3.73
4-0
5-4.51
6-4.74
7-4.74
8-9.0 vdc

[patrick398]

Also  the signal won't pass through the 511 k resistor but there is audio output at Pin 7 of the 072.

If you've got output at pin 7 there's no way R2 (511k) Is not passing signal.

[TK2]

Hi Pat Thank you for responding.. I get input From my signal Generator on the input side of the 511k resistor and no reading on the other(Pin 2 of the 072) side of the 511K resistor,, I'm not sure what's happening there..My reference is from Ground. If there is a signal going through,, It must be in the Micro volt range. When I take the 2399 chip out I get a strong input signal reading..  I have discovered another problem as well.. No continuity between the 1uF capacitor and the Top side or pin 3 of the Vol/level control,, I'll add a jumper wire to correct this problem tomorrow and take it from there...

[anotherjim]

You won't see or hear any signal on the -input of the op-amp. This is not a fault. The action of its output fed back (by R6 & C3) keeps the -input as a "virtual" ground (actually same voltage as the vref on the +input pin). As long as signal leaves the output pin, you're good.
The input pin16 of the PT2399 is also an op-amp -input, so same applies with input signal audible on its output pin15.

The output of the delay is pin14 (pin13 is another -input). If you can hear signal there, the chip is half working! Then if you turn the delay control you should hear the pitch bend.

All your test voltages look good. However, since many are meant to be close or identical readings anyway, it don't prove there isn't a fault, such as a short circuit between them.

[TK2]

Hi AnotherJim,,,Thank you for your Help,,, I must have checked to see if there was input the 072 pins initially with the Chip out just to check for continuity.. I've Found 4 disconnected traces and repaired those. I now have Volume control at the Center pin of the level pot but still no output level control outside the board.. I will check Pin 14 as per your instructions later on tonight...and let you know how that goes.. I'm wondering if it's not a bad ground somewhere,, Oh yes and still no effect into the 072... Brain and eyes are Fried.. will get back to it again.. Thank you for your Help,, really appreciate it.

[TK2]

PT2399 START UP PROBLEM SOLVED