Identify delay + repair

[stefcuypers]

Hello,

I got this delay from a friend. He bought it on evilbay and it was his precious toy since then.
Last week he fried it by putting 24volt through it and asked if i can repair it.

My first question, who knows which delay it is? It is digital for sure, it has a PT2399 chip.
Also and feedback loop with a VTL optocoupler.

Second, where do you start. What can be fried by 24 volt? Probably not the caps, resistors?

Thanks for looking,








Stef

[Mark Hammer]

It is a Scott Swartz PT-80:  http://www.generalguitargadgets.com/content/view/125/26/

Technically, if it has regulators, it should have been able to withstand a 24v adaptor.  But that presumes the correct adaptor.  Gotta say, I hope he got it for a good price because that solder job, in fact the whole board, is a sound argument for a) tinning your board immediately, and b) removing excess flux when you have a chance.

The other thing that is of concern is the large amount of exposed wire inside a very cramped chassis.  I won't snicker, because I've built much worse.  But then I didn't attempt to sell my wares on-line either.

One thing you may want to take a closer look at is whether that piece of masking tape over the pot is actually preventing any of the jack lugs from shorting out against it.

[Dan N]

Looks like a little modulation add-on there too.

[Thomeeque]

..and b) removing excess flux when you have a chance..

May I ask what is wrong with excess flux (concerning functionality and longevity of the circuit)?

I would definitely advice some protective varnish over the copper side of the PCB..

T.

[Thomeeque]

Second, where do you start.

I would probably start by checking supply current (should be up to let's say 100-200mA?) - If it's significantly bigger, I'd pull all socketed ICs and check again. If still, then I'd check protective diode and voltage regulators..

If supply current is OK, I'd continue by checking  supply voltages at all ICs, if they match with what each given IC expects (if they don't, I'd check voltage regulators), then I'd use some sort of audio probe to check where signal gets lost..

Good luck T.

[Mark Hammer]

May I ask what is wrong with excess flux (concerning functionality and longevity of the circuit)?
I would definitely advice some protective varnish over the copper side of the PCB..

Protective varnish is wonderful for things that are assured to be working.  For things that stand a chance of needing to be debugged, excess flux makes it VERY difficult to spot trouble visually.  In this case, as well, the large clumps of flux also seem to be a byproduct of having a board that tarnished due to exposure, prior to being populated, and needed "strong application" of solder to install parts.

In particular, in this case, the user has a pedal with a bunch of parts soldered in a rather "ad hoc" manner.  The flux makes it very difficult to tell whether the nonfunctionality is the result of a solder bridge or something else.

[Thomeeque]

May I ask what is wrong with excess flux (concerning functionality and longevity of the circuit)?
I would definitely advice some protective varnish over the copper side of the PCB..

Protective varnish is wonderful for things that are assured to be working.

Well, I have meant after it's fixed of course, as I see PCB corrodes a lot (or he can use solder-friendly varnish immediately)..

 For things that stand a chance of needing to be debugged, excess flux makes it VERY difficult to spot trouble visually.  In this case, as well, the large clumps of flux also seem to be a byproduct of having a board that tarnished due to exposure, prior to being populated, and needed "strong application" of solder to install parts.

In particular, in this case, the user has a pedal with a bunch of parts soldered in a rather "ad hoc" manner.  The flux makes it very difficult to tell whether the nonfunctionality is the result of a solder bridge or something else.

Yes, but I don't think that there is any trouble of this kind in this particual case.. it all worked fine until it was feeded by 24V PSU..

Btw. were not those 24V AC by any chance? In that case it's almost sure, that protective diode is burned (and there's a chance, that it now conducts in both dirrections and shorts PSU)..

T.

[Thomeeque]

But if I see it correctly now, there's a small resistor in series with PSU, it would probably burn first (most probably to non-conductive state).. check it first maybe.. T.

EDIT: It looks like this resistor is only one branch (for that small daughter board), there are (red) wires connected dirrectly to the PSU jack.. anyway, just start here and we'll see

[stefcuypers]

Thanks a lot Mark and Thomeeque for the help!
Will try the suggestions tomorrow.

But that presumes the correct adaptor.  Gotta say, I hope he got it for a good price because that solder job, in fact the whole board, is a sound argument for a) tinning your board immediately, and b) removing excess flux when you have a chance. The other thing that is of concern is the large amount of exposed wire inside a very cramped chassis.  I won't snicker, because I've built much worse.  But then I didn't attempt to sell my wares on-line either.

The guy who build it has died, his brother sold it on evilbay. So he probably didn't wanted to sell it. There is an protection plastic case over the board. It's not an amazing build but it worked till now!

Will debug and thanks a lot!