Need help repairing AC damaged Ibanez PD7

[chung3j]

I have a PD7 that got fried by plugging it in 9VAC. When it's switched off, it is the same as before. When it is turned on, it runs like its supposed to, but much quieter, and with a bit more noise. I took it apart and don't see anything that looks burnt, but I definitely smell it. What parts should I look to replace first? Also, when I started looking for the parts, I ran into a few problems. The IC's are JRC 4558D 3192K, which I can't seem to find exactly, but I find many called 4588 by different companies and schematics that look very similar. Are they interchangeable?

[JKowalski]

According to this schematic, there is a polarity protection diode. (D7)

Replace this diode and try it again. The diode doesn't have to be a specific type, any ol rectifier diode (ex 1n400X) is a good choice, small signal diodes would work well too I suppose since the only point of the polarity diodes is to fail anyways... Just get the correct orientation.

[Projectile]

Any 4558 will do, or an other dual opamp (TL072 etc). Although, only the 4558 sounds like a 4558, but it's a subtle difference. Just make sure you get the right package (not surface mount).

The first thing that's going to fail with reverse polarity are any tantalum caps in the circuit. Definitely replace those first. Also, the polarity protection diode might be damaged as JKowalski already stated.

[chung3j]

Sorry if I'm being ignorant, but is AC damage similar to reverse polarity damage?

[MartyMart]

Sorry if I'm being ignorant, but is AC damage similar to reverse polarity damage?

Yes, as DC is "Direct current" it stays in one "cable" (of your 2 pin power source) with the other to ground whereas AC "alternates" between the connections
so is just like putting the wrong polarity into your pedal.

MM

[R.G.]

Actually, AC damage is much worse than putting reverse polarity into your pedal.

Theoretically, it should not be, because AC is only the wrong polarity half the time, instead of all the time. In practice, putting 9Vac into a pedal first destroys the reverse protection diode, and then either burns the PCB under the protection diode or kills semiconductors and polarized caps, or all of the above.

I personally would "remanufacture" the pedal. I would replace every IC, transistor, and diode, and all polarized caps, as well as any resistor that looked like it had gotten too hot. That sounds like a big job. But so is replacing one thing, having something else fail in a week, fixing that, then having it fail again a week later.

[R.G.]

I forgot to mention a bit of philosophy on parts removal.

When you are removing parts from a board, it is simple to do if you can throw away *either* the parts or the PCB after you've removed them. Making this decision lets you destroy either the parts if you're keeping the PCB or destroy the PCB to get the parts off without damaging them. Both of these are much, much simpler to do than to remove parts without damaging either the parts or the PCB.

In this case, if you're remanufacturing, take good digital pictures of the board before you start so you have the original picture to refer to for part orientation and values. Then clip off the leads of the parts you're removing right at the body of the part. With that done, you can use the tip of your soldering iron to lift out the remaining lead. This works especially well for ICs; much simpler than trying to get the leads free inside the holes one at a time, then remove the part.

For two-lead components like resistors, clip off one lead, then melt the solder side of the remaining lead and lift the part out by the body and the one remaining lead.

A small wooden toothpick can be shaved down so it can be poked into the hole in the center of a pad on a PCB once the solder is melted. This then leaves an open hold for reinserting a lead of a new component.

[chung3j]

While I'm at it, is it possible, or rather practical to modify this pedal to true bypass?

[R.G.]

While I'm at it, is it possible, or rather practical to modify this pedal to true bypass?

It is possible, and practical, but a bad move to do when you don't have a working pedal to start with.

Get it working correctly first, then mess with any bypass mods.

When you get to there, I highly recommend using a true bypass box outside the pedal rather than hacking up the inside of the pedal.

[chung3j]

I went to mouser looking for parts, and found 2, opa2604ap and opa2604apg4. They both have the same specs, but apg4 costs 50 cents less. Why is that?

[R.G.]

I went to mouser looking for parts, and found 2, opa2604ap and opa2604apg4. They both have the same specs, but apg4 costs 50 cents less. Why is that?

I don't know. I did a cursory read in the datasheet and didn't find anything. They're both 8 pin DIPs. Pick your poison.