Thermaltake PurePower 420w W0052

[ipman]

This power supply is entering in protection as soon it's plugged in.
The failure is in stand-by power for sure.
Found one component burnt, marked as a D503 (diode) on PCB, but nothing on it.
I suspect this diode to be a 5V Zener.
I am attaching two pictures, with explanations about the circuit, maybe somebody can confirm my supposition.

[ipman]

Re: Thermaltake PurePower 420w W0052

Here is the schematics. D2 is the unknown diode which had burnt PCB underneath.
D1 is just a switcher, and the rest of the components (inductors, capacitors, etc) are just fine. With D2 removed I get some 7V on stby and the PS goes into protection.
I guess that this +5v goes to power another part of the PS, but can't figure out yet where.

[c_hegge]

Re: Thermaltake PurePower 420w W0052

I don't know for sure, but my guess is it's a 5.1v, 1W. I think it's there to short and either trip the protection or blow up the switching transistor in case of a worstec-style 5vsb overshoot, which will save the motherboard. Before replacing it, replace ALL capacitors associated with the 5vsb (even the tiny ones without vents), since they usually only overvolt if the 'killer 5vsb cap' fails.

EDIT: I think D2 might be around the wrong way in your schematic

[ipman]

Re: Thermaltake PurePower 420w W0052

All tow caps in that rail are 16V and seems to be ok. C2 is a 1000uF/16V and C1 is a 470uF/16V both made by Teapo.
My supposition was also that diode was a Zener 5V, because otherwise there is no component to stabilize the 5V rail. I found it charred and shorted and removed it, but there is no markings on it, just a glass diode.

Sorry, you are right, it's supposed to be the other way around.

[everell]

Re: Thermaltake PurePower 420w W0052

We all seem to agree that the burnt diode is a zener protection diode. But replacing it will NOT solve your problem. This is most likely a two transistor 5vsb circuit. As the circuit goes overvoltage, the zener draws high current until it shorts and burns up. While it is drawing high current, it is damaging the rectifier. Going overvoltage is also damaging the output filter capacitors (which need to be replaced). The problem area is most likely one of the LITTLE capacitors near the 5vsb transformer which is causing the overvoltage problem.

"In my opinion"..............putting a protection zener on the 5vsb circuit is a very poor bandaid for protection. As you can see, it only causes lots of additional problems in the power supply. Build a small adapter board with one of the currently available pwm chips to use in your 5vsb and it will shut down if it detects high current. Easier to troubleshoot and it doesn't cause so much burn damage to the pc board and damage to other parts.

Even if you replace ALL capacitors in that circuit, you might have damaged the rectifier diode, the two transistors, or maybe even the transformer. Some of us have attempted to repair a two transistor 5vsb circuit only to have it blow up a second time (or third time, or fourth time...).

[ipman]

Re: Thermaltake PurePower 420w W0052

This is the complete schematic, no other parts. I've ommited one trace that feeds an integrated circuit SG6105D which does allmost everything on control part, but it's not something active.
Strange, there is no other way to regulate voltage than this zenner diode.
The closest cap to the transformer is C2 1000uF/16, which is way above 5V and seems to be OK measuring ESR.
The rectifier before the Zenner is quite big, seems to handle much more than just 2A as indicated on sticker. I've pulled one leg out of circuit and shows normal behaviour when measured with a multimeter.
@Everell: can you please tell me how a two transistor stand-by is made?

Forgot to tell that PS is in fact made by Sirtec. It's written on the PCB inside.

[goodpsusearch]

Re: Thermaltake PurePower 420w W0052

Even if you replace ALL capacitors in that circuit, you might have damaged the rectifier diode, the two transistors, or maybe even the transformer.

How it can damage the transformer?

[everell]

Re: Thermaltake PurePower 420w W0052

Winding to winding shorts

[Toasty]

Re: Thermaltake PurePower 420w W0052

>>This is the complete schematic, no other parts.<<

I disagree. There must be more components involved. The 5vsb is not a free running circuit, nor is it a "linear" supply, and, as Everell mentioned, is likely controlled by a 2 transistor circuit. The input to the transformer is controlled by the 2 transistor circuit. Feedback is provided via an optocoupler to the 2 transistor circuit for regulation.

The zener is simply a protection device. When 5vsb exceeds the zener's ratings, it essentially "crowbars" the supply. If it shorts (as seems to be the case here) it shuts off the 5vsb and causes other destruction within the PSU. If it fails open, then destruction of the motherboard will probably follow quickly.

>>I've (omitted) one trace that feeds an integrated circuit SG6105D which does (almost) everything on control part, but it's not something active.<<

The 5vsb supplies voltage to the SG105D until the main supply comes on and then it's power is supplied by that side of the circuit. The 5vsb is then "cut-off" by the main side.

[EDIT: The failed cap is usually a small value ~47uF @ 50v in the 2 transistor circuit.]

Toast

[ipman]

Re: Thermaltake PurePower 420w W0052

@Toasty: Do you mean the small failed cap should be on the high-voltage part of the power supply? Before the transformer?
Or to put it in another form, those two transistors are the main transistors on a heatsink on the high-voltage side?
I ask about this because the voltage of this cap is too low to be in the high-voltage side.

Indeed, this diode was shorted, but I need to find out why.

[c_hegge]

Re: Thermaltake PurePower 420w W0052

Yup the two transistors and the 'killer cap' are located before the transformer on the primary side. One of the transistors will be bolted to the heat sink and be about the same size as the switching transistors, and the other one will be a small one.

[dumpystig]

Re: Thermaltake PurePower 420w W0052

Reading the above posts suggests to me that maybe this PSU is of a shoddy design/build - is this a good assumption on my part?

[c_hegge]

Re: Thermaltake PurePower 420w W0052

Not really. I had a PSU just like it (with a similar problem). It actually looked like a good unit, let down only by the 5vsb circuit. On my one, though, rather than the PSU shutting down, the shorted zenner diode blew up the switching transistor, and the PCB in that area was kinda damaged too, so I just scavenged the fans and wires from it.

[ipman]

Re: Thermaltake PurePower 420w W0052

The Thermaltake PurePower are in fact manufactured by Sirtec.
Seems to be a nice clean design and good quality.
Indeed, on the primary side there are a TO220 capsule and two bigger ones TO247 and all seems to be MOSFET's. I will check them and inspect the schematics as soon as I get back home.

[dumpystig]

Re: Thermaltake PurePower 420w W0052

That's what I'm dwelling on - quality. As far as i know Thermaltake (amongst many others) are meant to build quality (and therefore more expensive) components/accessories. Reading a few of the above posts makes me think sometimes it's a case of manufacturers relying on their reputation more than the actual integrity of the design and build quality of their equipment - I've definitely found this to be the case over the years.

[ipman]

Re: Thermaltake PurePower 420w W0052

Not all Thermaltake PS are made by Sirtec, just PurePower series.
The other ones are worse, TR2 series, got several others also, can't figure out what's happening. Will post about them in another thread.

[dumpystig]

Re: Thermaltake PurePower 420w W0052

Do Thermaltake actually manufacture any of their own equipment or simply slap their name on others stuff?

[ipman]

Re: Thermaltake PurePower 420w W0052

Indee, they are not manufacturing any PSU sold under their name. Everything is outsourced to more or less known PS manufacturers.
They only manufacture cooling heatsinks, but not the fans which are also rebadged.

[c_hegge]

Re: Thermaltake PurePower 420w W0052

AFIK they make cases as well.

The OEMs for their PSUs are:

Purepower = Sirtec (now High Power)
Litepower = FSP
TR2, Toughpower = Channel Well/CWT
All others = HEC/Compucase

[dumpystig]

Re: Thermaltake PurePower 420w W0052

No surprise there then. i guess it's a (bad) sign of modern times. It seems these days you never really know what it is you're actually buying.