PT80 won't echo. Bad SA571?

[morcey2]

I (finally) finished my PT-80.  I got it all together and it sounds great.  If you want it to sound like nothing is there.  No echo at all.  So I start searching and find several other people have had the same problem.  One was a bad cap, another thread ended without a resolution.  I pulled out the handy-dandy audio probe and signal generator (15-year old strumming a guitar) and found that I get delayed signal all the way to pins 2&3 on the SA571, but not on pins 7 & 8, which are the output on the expander portion.

All the voltages I measure match the ones in this post almost exactly:

http://www.diystompboxes.com/smfforum/index.php?topic=66619.msg530558#msg530558

Exceptions are, no max1044, PT2399 pin 7 = 0.22V, PT2399 pin 8 = 0.57V, and SA571 pin 16 = 0.88V.

I know that the PT2399's are really static sensitive and I was very careful when handling it.  I have a static-safe workstation for stuff like this.  Same with the SA571, but I thought it was a much tougher customer.  On pins 6, 7, and 8 of the SA571, I'm measuring about 25k resistance to ground, so it doesn't seem to be grounding out.  Can anyone think of anything I'm missing?  I don't have a spare at the moment, otherwise I'd just swap it in. 

Matt.

[morcey2]

Give me a bump, Vasili. One bump only, please.   (with apologies to Tom Clancy).

[slacker]

If you're getting delayed sound on pins 2 and 3 of the SA571 but not on pins 6 and 7 then it could mean it's damaged. That would mean only half the chip as damaged though and the other half must be Ok otherwise you wouldn't be getting any delay. That makes me think it could be something else, I'd double check the connections round pins 6 and 7 and check the pots are wired correctly.

[morcey2]

Thanks Slacker. 

I found this post:
http://www.diystompboxes.com/smfforum/index.php?topic=158.msg1670#msg1670
and followed it and determined that the 571 was working just fine.  At that point I noticed that the wet compressed signal coming from the 2399 was much lower than I expected.  I think what was happening is that the signal was low enough that it was being expanded downward, just like noise.  I started checking the components servicing the 2399; lo and behold, the 0.1u cap connecting pins 9 and 10 was only 0.001.  Not sure how that happened.  I'm sure one of my kids distracted me and swapped it when I wasn't looking.   

Swapped that out and it sounds great now!  The only problem with it now is that if the repeats knob is maxed, I get a really wierd high pitched growing echo.  I probably have something else wrong, but if I keep the repeats down, it sounds really good. 

Matt