Small Time Delay voltages?

[MrStab]

hi guys,

it's hard to pull the right results when searching for these terms, so apologies if this has been covered before. as the latest in my string of failed-pedals (hey, it's therapeutic just putting them together), i was wondering if anyone could write out their IC voltages (& maybe tranny voltages etc) from a working Small Time Delay?
i used this schematic: http://www.sabrotone.com/?p=2785 .

at first i got some weird (awesome) feedback, which i was able to control with the pots, but had forgotten a jumper near the opamp. so i put that in, now i just get the bypassed signal. tried removing C17 and jumping D & S on the J201 i used - no dice. so i don't think it's a switching problem.  i was getting the infamous lockup when the delay "section" did work, fixed by cycling the power.

i think my PT2399 might be screwed (sucks as i have no replacement ), but the same thing happens without it in the socket at all so worth trying other stuff i suppose. i managed to diagnose the aforementioned missing jumper with an audio probe, but i have difficulty with more complex stuff because i'm a bit of a simpleton. lol

cheers!

[ECistheBest]

pin 1 5v
pin 2 2.5v
pin 3 0v
pin 4 0v

and pin 10~18 should all be 2.5v

my initial try only had the bypass sound with NO delay at any setting. my problem was pin 4 (digital ground) had some high voltage (around 3.5v i believe?) and also the chip was warm. i jumpered pin 3 and 4 (analog ground and digital ground) and it fixed the problem.

[MrStab]

thanks EC! you mean 16 pins, right? or are you counting the TL072 & PT2399 together?

in any case, here're my results from the PT2399:

Pin 1 = 5
pin 2 = 2.5
pin 3 = 0
pin 4 = 0.14
pin 5 = 5v
pin 6 = 2.5
pin 7 = 4.66
Pin 8 = 0
pin 9 = 2.5
pin 10 = 2.5
pin 11 = 0.5
pin 12 = 4.86
pin 13 = 2.5
pin 14 = 0.2
pin 15 = 2.5
pin 16 = 2.5

clearly something's not right there. i'll have a look around to try & see if i can narrow it down a bit. any suggestions? tried jumpering 3 & 4 already, no luck

[ECistheBest]

i meant pins 9~16. the whole right side should all be at 2.5v if you're using it right.

did you get the trace cuts under R21 and R23? pin 11, 12, 14 seem wrong.

[MrStab]

just double-checked for the cuts you mentioned - they're all there, no obvious shorts but i'll check continuity.

yeah, just a handful were wrong on my failed Little Angel chorus build too so it's like reliving a bad dream lol. should Pin 4 be showing 0.14 or just straight 0?

i guess i could have another go with the audio probe. it's like a maze, i always wind up just trying to compare it with the layout best i can and try to rule out faulty parts. i think we can rule out opamp A at least... on the plus side, at least i'm not too bad at building buffers/boosts (by accident)! lol

[MrStab]

probably no help, but i can't think of anything beyond a damaged chip. either way, here're some pics of my amazingly-bad efforts, if anyone wants to have a look and correct anything. tidiness is not my strong-point and i'm still a beginner, so bear with me!
(also, i'm aware of poor practises eg. how i've secured some wires, but they were temporary fixes anyway)

C22 and C19 are propped up by extended legs and R8 is 3 resistors stuck together, in case it looks weird, but nothing touching as far as i can tell. voltages, schematic used etc. mentioned in previous posts. C17 removed in attempt to fix, apparently not crucial, though. i took pics from a few angles. thanks in advance if anyone wants to waste their time on this abomination!

[MrStab]

bump?

i'm starting to get a basic understanding of the PT2399 pins, enjoying learning here even if i have jumped into the deep end. repeatedly. i think i get most of it except the integrator pins.
assuming it might not be a dead IC, can someone approximate where in the signal path there might be a fault (from the voltages i listed earlier)?  otherwise i'm just gonna leave it until i can afford to order new one (clearly a highly-successful musician here!! lol).

cheers & sorry for the bump!

[slacker]

Look around pin 11 for something shorting it to ground, could be a solder bridge or a wrong connection. If you find this and fix it you will probably find the voltage on pin 12 fixes itself, pins 11 and 12 are the in and out of an inverting opamp so if something is pulling the input down the output goes up.
Do the same thing for pin 14, looks like it's shorted to ground, could be only a partial cut in the vero between pins 14 and 3.

If you have an audio probe you can check to see if you're getting signal to the PT2399, you should get sound on pin 15 and a loud noisy signal on pin 10.

[MrStab]

thanks for the tips, slacker.

checked continuity between 3 and 14, doesn't seem to be a short there. audio probe shows signal on pin 15, but no noise as you describe on pin 10. tried re-soldering C13 and double-checked all the components in that path (leading until Repeats lug 3, i think). damnit, the 3/14 cut thing was a really good idea, i was hoping that would be it! lol

well, the possibilities are getting narrower i suppose... do the latest clues affect the diagnosis any?

[MrStab]

looks like all i can do is poke around for a day or so and see if it's worth the ~£5 GBP to get another PT2399 sent out (it was at least good to begin with, so i trust the seller). thought maybe the jumper under it might be shorting something, but doesn't look like it. it'll be at least a coupla days before i get round to it, maybe longer, so if someone thinks of something in the meantime, let me know! totally stumped. DIYStumpedBox!

cheers!

[gcme93]

All i could imagine is one of R9 R10 or R11 being the wrong value? I guess you've checked them all over. I'm a little worried as this was one of my next projects (from Sabro's layout too)

Let us know if you get any further please!

[samhay]

If I understand your first post, the PT2399 probably did work but got fried because you missed a jumper somewhere - which one? - then locked up and now doesn't work? Does it pass clean signal whether bypassed or not? (it should with the mixpot set dry).
If so, I am struggling to see how a healthy PT2399 will give you the voltages you posted, so I susspect you might be best of with a new chip. I buy mine by the 10 from ebay. Not for the faint of heart, but definitely a lot cheaper than £5 each.  Having a few spares is probably a good idea.

[MrStab]

although my eyesight totally sucks for reading colour codes (slight colourblindness), i'm paranoid when it comes to quadruple-checking resistors with a multimeter, so i'm doubtful tbh, gcme. but i get where you're coming from. other people on the comments section of that Sabro page have had success with the layout, with some switching or lockup issues but i think the were resolved with minor tweaks. give the comments under the layout a read if you haven't already.

it was the jumper to the left of the opamp, samhay. 5 b & c on the grid. i get a clean sound on or off, the LED/switch seems to work okay as does jumping Q1. yeah it's a bit pricy going by single units i'd imagine - it's actually more like £3, but there'd be postage as well. no harm in a new chip, at least if that's not the problem i'll have a spare.

cheers!

[MrStab]

3 for a £5er on ebay, sweet! buying more in bulk from abroad would be overkill for me, as my success ratio is 1.5 out of 5 builds now lol. fingers crossed! hope i don't kill these chips, too...

[MrStab]

tried a new PT2399... and it works! wtf! something's wrong if it works! lol

it's quite noisy (i hear that's just the nature of the PT2399 beast), i'm not sure the volume pot is working yet, and everything usually breaks when i try to put it into an enclosure, but i'm sure it shouldn't be too hard to sort all that out. given that i started all this barely 2 months ago and couldn't figure out how to make an A/B switch, i'm kinda stoked.

thanks again for the help in diagnosing this, mofos!