Fixing Power Supply - EEs welcome

[metroplex]

The power supply:
Enermax 650W ATX

The problem:
under a heavy load (XP2100+ or AMD 1.4 T-bird), +5V is about 4.5-4.68V
intermittently it goes to 5+V on a lighter load CPU.

What I found:
blown PCB trace
1N5819 Schottky diode, split in half

The PCB trace was connecting this diode to a jumper wire that connects to the +5V output plug. So basically the other end of this diode went directly to the +5V

Here's what i posted on another forum hoping to get a 2nd opinion:

The 1N5819 schotkky diode split its wig in my enermax power supply.

One of the PCB traces was connected to it, and guess what?

It leads right to the +5V "bus" that leads out of the supply.

Coincidence? I think not.

Since I can't really repair the PCB trace, I'm going to just get a new Schottky and jumper that right from its original position to the +5V. The PCB trace that busted led to a jumper wire, which lead to the +5V.

I can bypass the jumper wire and just go straight for the kill (hopefully).

Its a 40V/1A diode, apparently it just rectifies/does something to the +5V to regulate it - whenever a heavy load is placed on the supply, it just starts zonking out (JUST the +5V).

Does it sound like the culprit? It was literally split in half. I could see the inside of the diode. my diode tester showed it was an open circuit.

 

[Mark R]

Careful. It might be part of the over-voltage crowbar circuit.

Essentially, if an abnormally high voltage is detected it shorts out the power-supply. Hopefully, the PSU will shut down, but if it doesn't then the short circuit will eventually cause something important to blow cutting the power.

What else does the diode connect to, and in what orientation is it? This should help give some sort of clue as to what it does.

 

[metroplex]

Well the PSU wasn't working so i had to pull it open.

One of the PCB traces leading to the diode was torn up.

The negative end of the diode (cathode) was on the opposite end of the +5V, meaning the anode was contacting the +5V.

It was cracked in half when I saw it.

 

[metroplex]

the cathode is connected to the two thermal controlled fan connectors on the PCB (enermax uses 2 thermally controlled fans), and it also connects to Base/Drain of a transistor (no idea what it is, BJT/FET or else) but its themiddle connector.

the Anode just leads to the +5V plug (the plug that holds like a gazillion red wires to the PCB).

I don't get how the PCB trace blew. Either the diode wasn't healthy (cracked at the factory) causing an overload, or something was up.

THe diode was an OC according to my meter, and i noticed a split down the plastic cylinder of the diode - i used a screwdriver to inspect but it just split open.

 

[Keego]

Is this the only trace that's burned up? Anything around the burn, or is it burned up right AT the diode? If it's burned up before it, I'd assume it's hosed. Try replacing it and skip the trace like you said, just make sure the trace doesn't also jump to the back of the board in the middle or anything. Make sure to insulate whatever you are skipping with also

 

[KF]

I guess you know trying to fix a PC power supply on your own is not a good idea if you can possibly get it fixed under warrantee. Figuring out how a particular one is supposed to work by just looking at it is difficult.

A diode connected the way you describe will conduct to an amount limited only by something else in the circuit. Considing the circuit trace to it blew out, something in that circuit no longer limited the current, blowing out the diode too. That seems to mean something else is, or was, wrong besides the diode and the circuit trace. If the fault was temporary, fixing as you describe may work. If not, who knows?

I personally would not want to hook that power supply up to something valuable before I knew it was working right.

 

[metroplex]

I'm a senior in EE and have worked on more dangerous stuff than this

Its not hooked up to anything right now, but once i get a new 1n5819 installed I'll try it on one of my older computers first. Like i said, with a light load it will provide adequate +5V voltage.

However the Diode was cracked (doesn't look burnt), and the PCB trace does seem to be blown up (a peice of it is missing, and the copper for that line was lifted up a little)

Its just that diode and PCB trace that appears to be damaged.

the enercrap is no longer under warranty.