EVGA NEX650G power supply detecting a fault on startup.

[snipersquad100]

EVGA NEX650G power supply detecting a fault on startup.

Hello guys and girls, I bought this power supply about 5 years ago, l had it 2nd hand. it's been a good little unit up until yesterday when my pc turned off unexpectedly.

I took it apart today thinking bad caps are to blame however it all looks ok in there, not even much dust, I guess that filter is worth it after all.

I plugged it into the mains as you do while its guts are exposed all over the table and shorted the green wire to the ground potential and noticed the fun briefly spin.

I think I'm correct in assuming the microcontroller is detecting a malfunction on the secondary side hence stopping the secondary side from powering up.

I can't see any obvious problems, no magic smoke was released when it stopped working, there wasn't even a bang or a pop, it was like someone just cut the power.

I don't suppose Evga has released a schematic on this power supply?

Only stdby voltage present due to its fault state.

[stj]

Re: EVGA NEX650G power supply detecting a fault on startup.

check the output diodes and main transisters for shorts

[ChaosLegionnaire]

Re: EVGA NEX650G power supply detecting a fault on startup.

i think i see an apfc circuit with a 400v primary cap again! but need the TS to confirm whats the voltage printed on the primary cap as it isnt very legible from the pics posted.

well... im like the control tower air boss in topgun now... "godammit! thats twice!" in a week now!

[snipersquad100]

Re: EVGA NEX650G power supply detecting a fault on startup.

The main cap is 420v 330 uf.
What is a apfc circuit? and TS?

[snipersquad100]

Re: EVGA NEX650G power supply detecting a fault on startup.

A bit of an update, I found a shorted resistor R76 but I have no idea what value it is. Do you think EVGA will give me a schematic?

[stj]

Re: EVGA NEX650G power supply detecting a fault on startup.

resistors dont short - check the nearby stuff - specially the ceramic caps

[snipersquad100]

Re: EVGA NEX650G power supply detecting a fault on startup.

The resistor is toast then, did you see the pic?

[stj]

Re: EVGA NEX650G power supply detecting a fault on startup.

yes, i saw the pic, but it was murder - not suicide.
check for Hillary Clinton or shorted capacitors nearby.

[snipersquad100]

Re: EVGA NEX650G power supply detecting a fault on startup.

Shall I inform the old bill.

[stj]

Re: EVGA NEX650G power supply detecting a fault on startup.

i wouldnt - they are all masons!

[snipersquad100]

Re: EVGA NEX650G power supply detecting a fault on startup.

The murder took place in between one of the control ic's on the other side of the board. maybe that ic has also been killed, I want be able to buy that ic.
Dam murderer, if I get my hands on him I'll give him a good thrashing.

[stj]

Re: EVGA NEX650G power supply detecting a fault on startup.

you can get most i.c.'s from china for peanuts.
i would remove the carcase of the resistor and then meter each pad to ground and other places to look for a possible short.

[momaka]

Re: EVGA NEX650G power supply detecting a fault on startup.

you can get most i.c.'s from china for peanuts.

True... but did you actually try seeing if you can find a datasheet for that IC? I tried looking up the numbers and I can't get anything meaningful. The "6601" in the name suggested HIP6601 at first, but that's an 8-pin IC, so that's no good.

i would remove the carcase of the resistor and then meter each pad to ground and other places to look for a possible short.

+1

Do you think EVGA will give me a schematic?

No, but it doesn't hurt to ask, I suppose (though I'm 101% sure they won't give you a schematic... heck, I'd be surprised if they even reply to you.... or any of us for that matter )

On the other hand, perhaps ask them if they can at least give you the correct part number for IC2 (the IC that has the burned resistor under it), as I think that could help us in determining what's wrong.

Otherwise, based on the symptoms and what I see in terms of topology in this unit... it looks like a modern single 12V rail unit with 3.3V and/or 5V derived from 12V via. buck converter(s). Therefore, it's possible that the upper MOSFET on one of these buck converter(s) may be shorted, thus trying to dump 12V into the 3.3V or 5V rail and the supervisor chip stopping it when it sees that. Given the proximity of the SMD MOSFETs to IC2 and that burned resistor, it could be that one of these is burned out. Thus, I suggest checking those MOSFETs (Q26, Q27, and Q28.) In addition to that, check for short-circuit / very low resistance between the 12V rail and the 5V rail, as well as the 12V rail and 3.3V rail. But when you do that test, make sure to give your multimeter at least 3-5 seconds to measure the resistance so that the output caps in the PSU have time to charge up from the meter. Otherwise, you might erroneously assume a short-circuit exists somewhere when it doesn't. Once you do these checks above, report what results you get back.

[snipersquad100]

Re: EVGA NEX650G power supply detecting a fault on startup.

Hello Momaka,
Q26,27 and Q28 seem ok but I did find a short on Q29.
Pin 1 is shorted to the tab as seen in the pic.
I cut pins 1 and 3 on Q29 to take it out of service as I don't have a soldering iron with enough thermal mass to remove the chip completely. Q29 then tested ok but the pads on the PCB where pin 1 sits are still shorted to the tab of Q29.
D18 is fine, R65 is a 2r resister going off to the via which I cant follow as it's in between that big inductor and heat sink? maybe it goes to those caps.

So the resistance between 12v and 5v rail is 13K ish
12v to 3.3v is in the megaohms, don't know what's going on there.

[kasfamily]

Re: EVGA NEX650G power supply detecting a fault on startup.

Ic2

[kasfamily]

Re: EVGA NEX650G power supply detecting a fault on startup.

https://www.fsp-group.com/en/knowledge-tec-13.html

[momaka]

Re: EVGA NEX650G power supply detecting a fault on startup.

Ic2
...
https://www.fsp-group.com/en/knowledge-tec-13.html

I guess my online searching skills are no match. Thanks!

Now the question is if there's actually a published datasheet with the pinouts of that chip.

Q26,27 and Q28 seem ok but I did find a short on Q29.
Pin 1 is shorted to the tab as seen in the pic.
I cut pins 1 and 3 on Q29 to take it out of service as I don't have a soldering iron with enough thermal mass to remove the chip completely. Q29 then tested ok but the pads on the PCB where pin 1 sits are still shorted to the tab of Q29.

Well, have a look at the circuit again. In particular, pin 1 - Gate - is connected to two 2R0 (2-Ohm) SMD resistors - R60 and R65... so that could well be why it was showing "shorted".

Before anything else, what I suggest doing is to use your multimeter on the lowest resistance scale (if Auto-ranging, then just use Ohms/resistance mode). Do NOT use diode test or "continuity" when checking for short-circuits, because these modes may not always give intuitive results. With the resistance setting, first touch both of your multimeter probes together and note the resistance. Depending on the multimeter you have, you should see as close to 0 Ohms resistance as possible (cheap meters can read up to 2-3 Ohms resistance with probes shorted together because of cheap wire used for the probes.) Now note this resistance down, because that would be your "short-circuit" resistance when you find something truly shorted on the board. And any resistance reading you do will probably be offset by that number (e.g. if your meter shows 1.2 Ohms with probes shorted together, then measuring something like a 2-Ohm resistor could show up as 3.2 Ohms instead of 2 Ohms.)

Now with that out of the way, do the following test if possible:
For each MOSFET (Q26, Q27, Q28, & Q29), measure the resistance from each of their pins (Gate, Drain, and Source) to PSU ground. Then repeat the result, but measure to the 3.3V rail. Then continue this way for the 5V and 12V rails.
Tabulate your results as follows:
MOSFET----PIN----GND----3V3----5V----12V
Q26-------Gate---Ohms---Ohms---Ohms---Ohms
Q26-------Drain---Ohms---Ohms---Ohms---Ohms
Q26-----Source---Ohms---Ohms---Ohms---Ohms

... then do the same for the other MOSFETs (Q27, Q28, and etc.) This should help us determine how these MOSFETs are connected in the circuit. I can already tell you that Q27 and Q28 are probably for the 3.3V rail DC-DC circuit, so most likely the Source of Q27 and Drain of Q28 will read very low resistance to the 3.3V rail.

All in all, your circuit design is probably very similar to Figure 1 in the link that kasfamily posted above. You can tell, because the big output toroid on your PSU has two different windings (two different wires), so it's probably the common toroid inductor for the 12V and 5V rails, and the 3.3V rail is DC-DC generated and has its own output inductor (the smaller one.)

So the resistance between 12v and 5v rail is 13K ish
12v to 3.3v is in the megaohms, don't know what's going on there.

Ok, that's good.

[kasfamily]

Re: EVGA NEX650G power supply detecting a fault on startup.

To easily unsolder lead-free solder, you need to add a low-melting alloy to it -for example - wood's alloy (metal) or rose’s metal

[snipersquad100]

Re: EVGA NEX650G power supply detecting a fault on startup.

Thank you everyone for your help.

momaka
I've made a chart with you measurements you asked for.

[momaka]

Re: EVGA NEX650G power supply detecting a fault on startup.

momaka
I've made a chart with you measurements you asked for.

Thanks.
However, are those really resistance measurements? Looks more like mV scale of diode test / continuity test to me. Most multimeters I know / have seen only do resistance accuracy down to 0.1 Ohms. So if you didn't do these measurements with the resistance test, please re-do them and post back. I'm still able to make sense of them for the most part (see below), but a true resistance measurement would reveal more. Otherwise, if you're 100% sure those are resistance values, could you please tell me what brand and model of multimeter you're using?

That aside, from the above table, I'm assuming that pin1 = Gate, pin2 = Drain (the tab / middle pin), and pin3 = Source. Is that correct? If yes, it seems things are connected as follows:

Q26 might be either a free-wheeling or forward rectifying device for the 5V rail (thus equivalent in function to either Q3 or Q4 in Figure 1 on the FPS article linked above.)

Q27 appears to be the upper MOSFET for the 3.3V rail DC-DC buck regulator circuit (i.e. equivalent in function to Q5 in Figure 1 on the FPS article.)

Q28 appears to be the lower MOSFET for the 3.3V rail DC-DC buck regulator circuit (i.e. equivalent in function to Q6 in Figure 1 on the FPS article.) However, there appears to be a mistake in your measurements, because you indicated that pin 2 (which should be the Drain) is OL to everything. But in fact we can see from the pictures in your PSU above that Q28 Drain (tab) is connected to the Source (pin 3) of Q27. Therefore, Q28 pin2 (Drain) should have shown the same measurement to the 3.3V rail as that of Q27 pin3 (Source) to the 3.3V rail. As such, I suggest you re-check the measurements in your table above, just to confirm what I'm stating here so that we can really understand Q28's function.

Finally, Q29... it also appears to be either a free-wheeling or forward rectifying device for the 5V rail (thus equivalent in function to either Q3 or Q4 in Figure 1 on the FPS article linked above.) Obviously if Q26 is one, then Q29 will be the other and vice versa. But again, I see a minor error here in the table - pin1 (Gate?) of Q29 shows as reading "1.92" to the 5V rail. I'm pretty darn sure this measurement is not in Ohms. If it really is, that may be a problem. But I really think you're using the continuity/diode test mode here and not resistance as I asked... so I can't actually tell if the reading is problematic or not. Also, when stating the resistances, please state the units too. I don't mean to make this into a high school science class all over again . But clearly "1.92" doesn't really mean much without units. If it's Ohms, that's no good for sure. If it's KiloOhms or MegaOhms, then it's a completely different story.