PSU havoc from hell!

[Artur D'Assumpção]

Hi guys,

I need to pick your brains for a moment!

A friend of mine just had his PSU completely blown up in a chain reaction from hell I must say!

Here are some photos of the incident:





Something really went wrong here as you can see! 

The first impression is that one of the bridged rectifiers went faulty. The AC from the transformer to the bridge rectifier or alternative the DC after the rectifier.

One of the output transistors shorted and therefore the other had to cope with this as also the bridge rectifier. Both causing the overheating of the wiring.

Do you guys have any clues or tips of what could have happen here? This really looks terrifying as also can distort the transformer/PSU and even causing a fire!

Also are there any type of protections/mods you can do to prevent this PSU blow up chain reaction?

Thanks guys o/

Cheers,

Artur

[waltzingbear]

That is by far the absolute worst failure of an SSL psu I have seen.

Without being on hand and testing it would be almost impossible to tell if it has unrecoverable damage.

I do see one item that is a little odd looking in the photo, that is the white wire that is not heated except by the edge of the chassis where the 240V tag is. And what appears to be a corresponding hole in the chassis upper edge. If what I seem to see is true, then that indicates a short that may be involved in the start of the incident. (wire to chassis)

This appears to be an early unit without the fuses on the mains. If they were present they may have prevented the meltdown, hard to say without understanding the cause. I believe that mod is already documented in the forum archives.

There may be damage to the contactor as well.

Time for a call to Xmax!

Alan

[Artur D'Assumpção]

Hi Alan,

Yes the suspicion on this is also those white leads. This is really bad, when I looked to it I already thought "is this even repairable"? The amount damage is impressive.

I was curious of what the opinions of the forum would be regarding to the possible cause, and it seems you also caught eye on the same probable cause.

I was also interested on some sort of mods that could have prevented this. Could you perhaps share the link of that thread you were talking about?

Thanks for the feedback! o/

Artur

[sintech]

Yes, this is the classic Bridge going short, and wires melting, due to lack of Fuses.

It always actually looks worse than it is.

You need to remove the wires from the barrier strips to the rectifiers, and check the AC secondaries, are good.

[Artur D'Assumpção]

Sintech,

It looks nasty like hell!

Is there in the forum a thread that goes through a mod on the old PSUs to add the fuses to prevent this from happening? I was trying to look for it but I couldn't find one...

Cheers,

Artur

[sintech]

If you check the G service manual, you can see the measures SSL took to avoid this kind of meltdown

[sintech]

This thread regarding the fuse installation: http://forum.sslmixed.com/index.php?topic=452.0

[Artur D'Assumpção]

This is perfect!

Thanks Sintech!

Cheers,

Artur

[sintech]

Do note: this looks like a Computer PSU, most likely E series.

Checking the G computer service manual available here, we have a PCB layout, but no block schematics. The +5v regulator diagram shows no fusing.

It would be cool to look under the lid of G series to see what line of protection was added.

[sintech]

Wondering now the correct mains fuse rating for the computer supply? After all this supply is IEC, and relying on the fuse in the plug to go.. maybe this caused more meltdown than normal.

[sintech]

Similar (but not as drastic) issue with James Lugo's Computer Supply from his SSL install series:

https://www.youtube.com/watch?v=8FuzLR0iATo

[marcmozart]

Side by side pictures of Console and Computer PSU. The PSU in this thread is indeed a Computer Power Supply.

http://forum.sslmixed.com/index.php?topic=580.msg3904#msg3904

[marcmozart]

Thinking about putting a smoke detector INSIDE each power supply. When something like this happens, you want to know at the earliest possible moment.

Similar (but not as drastic) issue with James Lugo's Computer Supply from his SSL install series:

https://www.youtube.com/watch?v=8FuzLR0iATo

[Artur D'Assumpção]

Hi guys,

Got some developments.

This was indeed in the Computer power supply...it seems there where never fuses on this power supply? It seems the audio PSU was much more protected than this one, and fuses on Audio PSU would have not prevented this havoc on the Computer PSU.

Even though, what seems is that the type of fuses we're talking about will only protect the DC wiring, and whatever happened here most likely happened in the AC wiring (transform to rectifier).

The protection for preventing this would normally be the current trip in the mains?

Any suggestions? I would love to hear your insights on this.

Cheers,

Artur

[michaeldtech]

I don't have any docs at hand but there would HAVE to be mains fusing.
Think of the current it takes to melt a 21 strand!  Divide by 10 for a DC fuse rating.
This has to be done forensicly by id'ing the voltage involved and removing everything before the melt. All mechanical contacts need to be new, or shiny-old. It is probably a cap that took things down. They should be done every 10 years in those supplies.
Rather than a smoke detector inside it is important for you to inspect them every 2-3 years. Give them a vac with a thin tube(I use an attachment made from multipair jacketing), look at the wire insulation at the butt of each crimp for any sign of heating, remove and clean lugs with isopropyl alcohol then tighten back, same with the bridges. Check the barrier strips and all the connections there. I put foamAC filter over the fan intakes but there is still micro dust on board. The heat, dust, and oils present in there create bad chemistry for mechanical connections. Clean and condition regulator board connectors and sockets. I use a declined credit card with a twill wipe over with alcohol to get in there. Pro gold on the edge contacts conditions both sides of the connection.
It's like maintenance of anything mechanical- here we have to maintain stationary mechanical parts.

I hope the comp is OK
Mike