Problem with PT80 stompbox

[martinpg]

Hi, I have built a PT80 stompbox using a kit from General Guitar Gadgets. When I power it up, I don't get any delay (though the guitar does sound louder than when it is powered off).

As far as I can tell, the PT2399 is not getting any voltage - at least none of its pins register any voltage. Working backwards I think that the voltage should be coming from pin 3 of the MAX1044. It looks like pins 1 and 8 of the MAX1044 are getting 9v, pin 2 has about 8v, and pin 3 is registering 0v. Do you think that this means I have a bad MAX1044 or is there a more likely explanation? Thanks for any help. Regards, Martin

[head_spaz]

Pin 3 on the MAX1044 is supposed to be connected to battery ground, so 0v is correct.
8v on pin2 is in the neighborhood, what are you reading on the inputs and outputs of the Vregs?
The MAX1044 will not tolerate an input voltage over 10.5v MAX, so be very careful or you'll cook that sucker.

[martinpg]

Hi, thanks for the response. I measured the (approximate) voltage on the pins of the various ICs as follows. Some of them do not match the specs provided by GGG, so I guess something is wrong, though I cannot diagnose what yet. If you can provide any pointers (such as a bad IC or where a short is likely) it would be appreciated! Thanks, Martin

Max1044
1 9.5v
2 8+v
3 0v
4 0+v
5 0+v
6 3v
7 7+v
8 9.5v

TL072
1 3.2v
2 3.2v
3 3.2v
4 0+v
5 0+v
6 3.2v
7 3.2v
8 7.0v

PT2399
1 0v
2 0v
3 0v
4 0v
5 0v
6 0v
7 0v
8 0v
9 5.5v
10 2.8v
11 0v
12 0v
13 0v
14 0v
15 0v
16 0v

PT2399
1 0v
2 0v
3 0v
4 0v
5 0v
6 0v
7 0v
8 0v
9 2v
10 6v
11 1v
12 1.4v
13 6.8v
14 1.6v
15 1.6v
16 0v

[martinpg]

Hi, I have studied the PCB circuit a little more closely and read other posts on the PT80, and I think that I have narrowed down my problem as follows: the "top" (closest to the edge of the PCB) legs of both the 78L12 and 78L05 read 8v (is this correct?), but the "bottom" leg of the 78L12 reads about 7v, and I think this should read 12v. So my question is: does this look like the "top" leg voltage is wrong, or is the 78L12 not outputting 12v as it should?

For the record, I mistranscribed the voltages on my PT2399, so these are the corrected ones. Thanks for any help, Martin

PT2399
1 5.5v
2 2.8v
3 0v
4 0v
5 0v
6 0v
7 0v
8 0v
9 0v
10 0v
11 0v
12 0v
13 0v
14 0v
15 0v
16 0v

[anchovie]

The 12V regulator should have a higher voltage going in to give 12V out - it can only "step down". A problem lies with/around your MAX1044, which should be outputting around 17V.

[mth5044]

Try checking the voltage after the second diode in the charge pump section.

You can see here on geofex, where the 17v should be coming out of.

http://www.geofex.com/circuits/+9_to_33.htm

It should be on the top most trace on the pcb, after the diode (not the one that connects to pin 1 of the MAX1044 if I'm reading it correctly).

If that isn't reading ~17v, then you have found a problem. Maybe you put the diodes or the caps in wrong? Maybe your MAX1044 is shot...

Anyway, if you get it working, could you let me know how it sounds? I've been wondering if the addition of the compander actually helps with the clipping on the repeats. Thanks!

[martinpg]

Thanks - this helped a lot in understanding how the charge pump works. Unfortunately, even after getting a replacement MAX1040 and double-checking this part of the circuit, I still could not the charge pump to work. I decided that the best thing to do was to try the version of the circuit without the charge pump which involves hooking up 16V to the bottom of the 12V regulator.

This gets the right voltage to the TL072, but neither of the other ICs, PT2399 and SA570 are getting the right voltages at most of their pins. I have tried to check for shorts on the PCB, and there don't appear to be any, but I don't have any other voltage check points to look at. Does anyone have a schematic with more annotations as to which voltages should be where?

Thanks for any help, Martin