only 4V on standby - EVGA 850 B2 SuperNova

[luvtrumpsh8]

Re: only 4V on standby - EVGA 850 B2 SuperNova

Gimme a break. you know an end user isn't going to have a fancy meter. the manual that comes with a $10 meter is a 2 page piece of crap printed in chinglish

[budm]

Re: only 4V on standby - EVGA 850 B2 SuperNova

Yep, $10 meter with poor safety to boot.
And if you do a little research:
https://electronics.stackexchange.co...for-resistance

[PeteS in CA]

Re: only 4V on standby - EVGA 850 B2 SuperNova

An N-channel MOSFET should measure extremely high resistance, regardless of which two terminals you choose. With a diode checker, putting the + lead on the source and the - lead on the drain should show a diode junction; in a resistance setting, those two MOSFET leads and polarity may read 100s of K-ohms.

[tom66]

Re: only 4V on standby - EVGA 850 B2 SuperNova

A single "1" on the cheap chinese meters means "overload", which is to say the resistance is >200 ohms.
It is also very uncommon for a primary FET to blow without taking the fuse out.
Have you tested the power supply by grounding PS ON and seeing if the outputs turn on?
It could be a fault with the motherboard, or something else.

[luvtrumpsh8]

Re: only 4V on standby - EVGA 850 B2 SuperNova

The "1" is on there with no leads touching anything so I don't think that can be overload, and when I tested a resistor it will go up to 4.7 or 100 or whatever so I think the meter is OK. Just holding the probes in the air causes a "1" ..

Basically there is no change from the "1" when I'm on the 200ohm setting no matter which sequence of pins I probe using any polarity yet under the same setting as soon as I touch something else the numbers move

It has no diode function , just ac / dc / bat / ohms

I'm going to change the part anyway since its out and has like 10,000 hrs on it but there seems to be no cross reference for it and I hate ordering online.

I might just wing it and buy a n channel mosfet by spec.

A single "1" on the cheap chinese meters means "overload", which is to say the resistance is >200 ohms.
It is also very uncommon for a primary FET to blow without taking the fuse out.
Have you tested the power supply by grounding PS ON and seeing if the outputs turn on?
It could be a fault with the motherboard, or something else.

[tom66]

Re: only 4V on standby - EVGA 850 B2 SuperNova

The "1" is on there with no leads touching anything so I don't think that can be overload, and when I tested a resistor it will go up to 4.7 or 100 or whatever so I think the meter is OK. Just holding the probes in the air causes a "1" ..

Yes this is normal. "1" means overload, i.e. >200 ohms. It is telling you the resistance of the air is more than 200 ohms. Which is good. Because if the air is conductive you're going to have a very bad day.

Basically there is no change from the "1" when I'm on the 200ohm setting no matter which sequence of pins I probe using any polarity yet under the same setting as soon as I touch something else the numbers move

This indicates that the MOSFET does not have a short, it could still be bad but the most common failure mode is short circuit, especially for high voltage devices.

I would look elsewhere at the moment unless you have other reasons to believe the MOSFET is bad.

I'm going to change the part anyway since its out and has like 10,000 hrs on it but there seems to be no cross reference for it and I hate ordering online.

I might just wing it and buy a n channel mosfet by spec.

Make sure you match: Vds (same or greater), Ids (same +/-10% or greater), Rds(on) (same +/-10% or lesser) and Qg (same or less). Those are the most important parameters to match. You should be able to find a direct replacement for the Infineon part from Digikey.

However, I would note that I am not convinced that this MOSFET has failed and you might be replacing a perfectly functional device. 10,000 hours is nothing for a good quality MOSFET. 100 million hours is a typical MTBF for a MOSFET that has not exceeded thermal or voltage margins.

[luvtrumpsh8]

Re: only 4V on standby - EVGA 850 B2 SuperNova

Thanks for the help. I'm starting to think more and more that it isn't the mosfet either because it still doesn't explain the loud pop and how I still have 5v. Because I have the second one I will desolder the related parts tonight while drinking and see what I find.

[R_J]

Re: only 4V on standby - EVGA 850 B2 SuperNova

Think of it as 2 power supplies, there is one small low current power supply that supplies the +5 volt standby to the motherboard, when the power button is pushed the motherboard tells the main power supply that supplies all the high current +12 + 5 etc to turn on.
there is some basic information here: http://www.smpspowersupply.com/atx-power-supply.html

[PeteS in CA]

Re: only 4V on standby - EVGA 850 B2 SuperNova

Over a couple of decades, MBs have used the 5VSB and (in servers) 12VSB for more functions than just power on control.

R_J has it right, one of the first things you need to do in troubleshooting is figure out what died - the main inverter, the Standby regulator, or the whole thing. I did just that a couple of days ago and my troubleshooting lead to finding that the primary Vcc created by the Standby regulator was shorted to primary return. Yesterday, in another unit, I found that the main 5V wasn't coming up and I discovered there was a shorted synchronous rectifier MOSFET. Your starting point tells you where to start looking and your understanding of the circuit and what you find lead you toward the solution.

[luvtrumpsh8]

Re: only 4V on standby - EVGA 850 B2 SuperNova

FAIL.

ended up scrapping it for copper. too many surface mount parts and tight areas and it looks like a waste of time to order parts when used ones are $50. this is truly a garbage power supply and I don't recommend it to anyone.

Thanks for everyone's help

[momaka]

Re: only 4V on standby - EVGA 850 B2 SuperNova

FAIL.

ended up scrapping it for copper.

Lol, what copper? Perhaps in the wires only. The rest is solder and aluminum mostly. Hardly anything on the PCB.

That said, you should sell it on eBay "For Parts or Repair". You will likely get at least around $10-20 for it, as there are people out there who can troubleshoot it and fix it easily.

And yes, it IS worth getting parts and fixing it, but only if you have the time and patience to find what is wrong. If you have neither, I can understand your situation.

But like I said, sell it online for parts. You will get a lot more money that you ever would when you scrap it for copper.

That said, I never understood the copper and gold scrappers on eBay, particularly the ones that do it with PC parts. Sometimes, they have rare PC components that they can sell for 10x the amount if only they did a bit of research before completely trashing the said component(s).