Help with Power Acoustik A3000db Repair

[wccoug21]

Hello, I'm trying to repair my PA A3000db. The power supply transistors were all destroyed so I will replace those 16. I checked the resistors in parallel and they are all within tolerance. The output transistors checked out fine except for 2, so I will replace those. Resistors checked out fine.

Two out of the five larger capacitors are bulging at the top, so should I replace all 5?

Also it looks like the black stuff from the outside of all the capacitors melted and got everywhere. Is there any way to remove this?

In general how do you figure out which are the driver transistors? I want to replace them.

Is there anything else I should check before ordering parts?

Thanks for the help.

[Perry Babin]

Hello, I'm trying to repair my PA A3000db. The power supply transistors were all destroyed so I will replace those 16. I checked the resistors in parallel and they are all within tolerance. The output transistors checked out fine except for 2, so I will replace those. Resistors checked out fine.

**** You need to replace all 10.

Two out of the five larger capacitors are bulging at the top, so should I replace all 5?

**** Does the bulging top go down then pop back up if you push on it?

Also it looks like the black stuff from the outside of all the capacitors melted and got everywhere. Is there any way to remove this?

**** That's fixative. It's there to prevent the caps from breaking their solder connections.

In general how do you figure out which are the driver transistors? I want to replace them.

**** Driver transistors for which transistors?

Is there anything else I should check before ordering parts?

**** Does the fan turn freely?

**** Does it operate with zero vibration?

**** If you stop it repeatedly, does it restart?

**** Q124 and Q125 need to be replaced. Replace them with MPSW42s.

**** Do you see any powdery substance where the windings overlap on the output filter inductors (see attached)? You may need to use a lighted magnifying glass to see it.

[wccoug21]

**** Does the bulging top go down then pop back up if you push on it?
No, it doesnt really push down, and one of them feels really loose and is able to turn.

**** Driver transistors for which transistors?
How do you know which ones need to be replaced in a situation like this. (Q124 and Q125 in this example)

And the fan looks fine.

**** Do you see any powdery substance where the windings overlap on the output filter inductors (see attached)? You may need to use a lighted magnifying glass to see it.
Not really powdery. But there is a yellow substance that looks like flux under the windings.

[Perry Babin]

If the plastic tops don't go down then pop back up, the cap may be swollen. You'd need to remove the plastic disc on top of the cap to see if it has vented or is bulging. Don't remove any more of the shrink-wrap from the cap than necessary to get the plastic disc out (see attached).

If you see something like the powder shown in the photo, the enamel is wearing through. This is often the reason the outputs fail. You need to get an insulator in-between the windings. I use 80lb test dacron fishing line. Get it around the winding (1 or 2 strands) and pull it up into the tightest place between the windings.

I believe that Q124 and Q125 need to be replaced because they virtually always need to be replaced when the outputs fail. Even when the outputs haven't failed, they often need to be replaced.