Leaking Capacitors inside PowerBook 500 Series Power Supply

[Ferrix97]

Hello!

I recently scored a couple of PowerBook 540c, together with three power bricks!

When I plugged the first one, I heard a loud POP! noise coming from the power supply.

I decided to open it using the vise and and after desoldering the bottom shield, I quickly found out what happened:



It looks like one of the capacitors leaked its electrolyte, which found it's way between the shield and the PCB, shorting two tracks together.

The capacitor that leaked was a 100uf 25V, there are only two of them on the board and they are very easy to replace



Currently the Fuse (3.15A 250V F) is blown, and I don't have a replacement on hand, but it looks like the rest of the circuitry is fine.

I'll report back once I get a new Fuse, which can be replaced without removing the bottom shield, it is in a holder soldered to the PCB, to remove it you only need to desolder one of the connections, the holder can be reused.

 

[Paralel]

Out of something like 5 blackbird power supplies, I've only found on that was still any good, the rest were goners

 

[Ferrix97]

Quick Update:

I installed a 2A fuse, powered it up and it didn't blow!, But I have no output.

once I get some free time, I will see if some other component or track failed

 

[MikeatOSX]

Interesting thread!

Did you destroy the casing by using a vise or is there a way to open it without damage?

BTW: I have a power supply which powers the PB but doesn't load the battery (vBatt is 0,7 V).

 

[Ferrix97]

The tho halves of the case are welded, so brute force is required to open it.

The vise seems to be the best way to open power bricks, just clamp the brick near the junction point and apply pressure.

once you are inside, you need to desolder a little "tab" holding the bottom shield, then you can lift one side of shield and replace the two capacitors (one on the left and one on the right).

The interesting fact about this power brick is that inside there are two separate and independent power supplies, so it's possible that one is failed and the other one still works fine. The input protection, filtering and rectification (essentially the "primary" side) is in common between the two supplies, the rest is separate.

Maybe (haven't looked at the circuit in detail) the two (100uF) leaking capacitors are used for "bootstrapping" the supply when it's turned on. If that capacitor is bad, your power supply won't start and you will get nothing on the output.

 

[MikeatOSX]

Very useful infos! Thanks!