Broken delay

[Organtis]

So I made a OfferUp purchase and found out the delay I bought was broken.  It works fine in bypass and then gives out some faint noises and then stops. 

This sounds like a capacitor to me.  Is there a way for me to test them on the board.  I don't see any bulging.

This is a joyo digital delay.  I figure even if it's a bust at least I got an enclosure and some parts.

[deadastronaut]

from what ive read its a pt2399 delay..

if its fried , stick a tonepad rebote 2.5 in it...

or if you want tails too put merlins 'small time delay in it..

both are cool and  will go in it.

[Organtis]

Do you think that could be the issue.  I haven't removed anything from the board yet but I can't see any visual signs of damage.  I'm thinking of pulling components off the board and testing them individually.

When I engaged the pedal it made some shrill oscillating sounds and then quickly faded.

[garcho]

I'm thinking of pulling components off the board and testing them individually

don't do that. use an audio probe to find where the audio signal is good vs bad (or missing). keep in mind, just because it "seems" like audio should be at a particular junction doesn't necessarily mean you'll get audio via probe, but it can be a big help for troubleshooting.

if the caps were bad you'd most likely have DC on the jacks, or 60/50Hz hum from the mains. i doubt it's the caps. caps need replacing on old gear, usually not on new stuff (unless the part is faulty, which is rare).

do you have a DMM? if there's a PT2399 in there, there will also be a 78L05 5V regulator. voltage regulators have a way of going bad, especially low-voltage regulators (compared to the PS voltage)

[Organtis]

Thanks for the tips.  I know the resistors test good and none of the caps look bad.  I tested the switch as well as the wires from the switch to the board....  So you think the ICs are the logical step? Maybe there is a way to test the regulator.

[blackieNYC]

If there's a problem with the pt2399, it should still pass dry audio, no?  Check voltages.
Surface mount?

[garcho]

it's all through-hole, crazy. and is that NOS philips NE571? why? companding the janky PT2399, i guess, but it seems odd Joyo wouldn't make this SMT doesn't it?

take voltages and post them. do you have a voltmeter/multimeter/DMM? how about an audio probe?

it should still pass dry audio, no?

good point.

[Organtis]

Thank you all for the help thus far. I am a beginner and this is very helpful.

So I still cant get any sound out of it besides shrill oscillation with all pots on full. I have had this pedal before and I know it self oscillates on full.

Well I got some numbers but I don't know what they mean. I don't have a audio probe but I want one after reading about it.

Op Amp RC4558 (Which is extremely hot)

1. Output 1   8.5v
2. Inverting input 1   8.5v
3. Non inverting input 1   4.5v
4. Negative Supply   0v
5. Non inverting input 2   4.4v
6. inverting input 2   8.4v
7. output 2   8.4v
8. Positive supply   9v

Compander SA571

1. Rect cap 1   .85v
2. Rect in 1   1.8v
3. Delta G cell in 1   1.8v
4. Ground   0
5. Inv in 1   1.8v
6. Res r3 1   6.8v
7. Output 1   6.8v
8. THD Trim 1   1.8v
9. THD Trim 2   1.8v
10. Output 2   6v
11. Res R3 2   1.8v
12. Inv in 2   1.8v
13. Vcc   9v
14. Delta G cell in 2   1.8v
15. Rect In 2   1.8v
16 Rect Cap 2   1v

PT2399

1. Vcc   5v
2. Ref   2.5v
3. AGND   0
4. DGND   0
5. CLK_O   3v
6. VCO   2.5v
7. CC1   4v
8. CC0   4v
9. OP1-out   2.5v
10. OP1-in   2.5v
11. OP2-in   2.5v
12. OP2-out   2.5v
13. LPF2-in   2.5v
14. LPF2-out   2.5v
15. LPF1-out   2.5v
16. LPF1-in   2.5v

Im kinda thinking its weird that the whole right side of the PT2399 was 2.5v? but the pots were all maxed... does that mean my inputs would equal my outputs or is this toast?

[mth5044]

Looks like GGG's PT80.

[garcho]

the op amp voltages are screwy, check there

[Organtis]

Yeah it does look very similar to the PT80.....and I found this https://www.muffwiggler.com/forum/viewtopic.php?t=67076&sid=161c8d27812c5caedfa017ccd75e4539

by looking at this I am thinking there is something weird with the Op Amp as you said Garcho..... plus it is extremely hot like you can hold your finger on it not more than a second.

So based upon that do you think the answer is that it needs to be replaced or since the voltages look too high am I looking for a bad resistor?

while I was at it tonight I remelted all the solder points.

[bluebunny]

Op amps will do whatever they can to make the inputs the same.  These are 4V apart.  Your op amp may be toast and some culprit may have killed it.  Seek him out!    (What are the readings with the op amp removed?)

[anotherjim]

I can't see any diodes on that board, so it may not have any protection against reverse power supply. As already seen, the 4558 op-amp looks bad - it's got 1/2 supply ok on the + inputs but the outputs are stuck up near the + supply. PT2399 looks ok and it has some protection from it's 5v regulator so may well still be good. The 571, we can hope is ok, I don't know that chip well enough - everytime I look at it's datasheet, I fall asleep.

[Organtis]

Well at a cost of .40 each I bought two and we will see what happens when I replace it.

Thanks for all the help I will report back in a week.

[Organtis]

I said I'd report back and it was an udder failure. Pun intended. 

I think my tip was too large or the board is cheap because trying to braid the solder up and getting the old chip out I think I burned the pads up and some of the board peeled up then I was just chasing my tail to figure things out. 

Decided it was toast and I am going to use it for parts.  I got a good enclosure and a good 3pdt switch though. 

[cloudscapes]

I've seen more companders/571s die than pt2399s in commercial pedals. small sample size, but still..

[nosamiam]

I said I'd report back and it was an udder failure. Pun intended. 

I think my tip was too large or the board is cheap because trying to braid the solder up and getting the old chip out I think I burned the pads up and some of the board peeled up then I was just chasing my tail to figure things out. 

Decided it was toast and I am going to use it for parts.  I got a good enclosure and a good 3pdt switch though.

For future reference if you didn't already know: did you cut the legs of the IC before you tried to get it out? If it's something cheap like a common opamp, try using some side cutter/wire cutters or a Dremel cutoff wheel to cut off all the legs and remove the body. Then you can attach each leg individually. It's much easier on your sanity and on the PCB. If you have an irreplaceable IC of course you can't do this.

Be careful if you're using wire cutters. If your PCB is really delicate, you can do some damage to the pads due to the mangling of the legs while you're clipping them. They really aren't the right tool for the job but they work.

And if you already know this, disregard. But maybe someone else doesn't. I learned this one the hard way and have become really good at desoldering due to so many screwups.

[garcho]

I think my tip was too large or the board is cheap because trying to braid the solder up and getting the old chip out I think I burned the pads up and some of the board peeled up

i don't like desolder braid, have you tried one of these? they're cheap and work better than braid in my opinion.


it sounds like you applied the soldering iron for too long, as opposed to having a tip that's too big. it's not a conical tip?

i socket all ICs and transistors, since if something does go wrong with the pedal, they're often first in line to get fried. you can hot-glue them if you're afraid they're not secured in place well enough.