1300W PSU - Help with replacement mosfet

[sdinelli]

Re: 1300W PSU - Help with replacement mosfet

the 10k resisters are good. i took them out of circuit along with one of the fets in yellow ( the one on the end because it was easy to get out)
it turned on and off as it should.
so it looks like i can get away with replacing the one main fet ( ill probably replace both), diode and the through hole resistors.

hopefully i remember where all the stuff i took out goes haha
jk

ill order parts and report back when its installed.

i still have to make the light bulb current limiter thingymambob

[sdinelli]

Re: 1300W PSU - Help with replacement mosfet

Actually can someone help me identify the specs of these resistors?
I really suck at this for some reason
they seem like metal film 2watt
2x 5.8ohm.05%
1x 65.9ohm.05%

What do you all think?

[tbgaming]

Re: 1300W PSU - Help with replacement mosfet

You technically already did. The specs are as such indicated by it's color bands.

[sdinelli]

Re: 1300W PSU - Help with replacement mosfet

You technically already did. The specs are as such indicated by it's color bands.

Well what if im color blind?? :P

I guess im just looking for reassurance before i order. im just guessing on the 2 watts too does that sound about right?

[R_J]

Re: 1300W PSU - Help with replacement mosfet

The resistors are likely ok based on your first post?

[sdinelli]

Re: 1300W PSU - Help with replacement mosfet

The resistors are likely ok based on your first post?

But they measure very low about .03-.04ohms

[R_J]

Re: 1300W PSU - Help with replacement mosfet

But they measure very low about .03-.04ohms

They are very low values, resistors very rarely go down in value. When I first looked up the values they came to 0.05Ω
Using the 4 band color code, they read 0.05Ω 5%

[sdinelli]

Re: 1300W PSU - Help with replacement mosfet

They are very low values, resistors very rarely go down in value. When I first looked up the values they came to 0.05Ω
Using the 4 band color code, they read 0.05Ω 5%

well why do they have 5 bands then? its confusing which is why i asked in the first place.
Whats the point in having such a low resistor there? does it act as a fuse?

If you did measure them as 4 band they would still measure lower then spec
which leads to ask do i replace them with 4 band spec or 5 band spec resistors?
:/

[sam_sam_sam]

Re: 1300W PSU - Help with replacement mosfet

well why do they have 5 bands then? its confusing which is why i asked in the first place.
Whats the point in having such a low resistor there? does it act as a fuse?

If you did measure them as 4 band they would still measure lower then spec
which leads to ask do i replace them with 4 band spec or 5 band spec resistors?
:/

Here is the answer to your question

https://www.digikey.com/en/resources...tor-color-code

Use the calculator for 5 and 6 band selection and you see what each band is for

[momaka]

Re: 1300W PSU - Help with replacement mosfet

well why do they have 5 bands then? its confusing which is why i asked in the first place.

Sometimes there are 4-band resistors with a 5th band that stands for "reliability", IIRC. This is different than regular 5-band resistors, where the first 3 bands are the value of the resistor, the 4th is the multiplier, and the 5th being the tolerance. In this case here, I think we are dealing with the former.

Whats the point in having such a low resistor there? does it act as a fuse?

Current sensing + fuse.
Despite its low resistance, a significant voltage rise can appear across that resistor when a very high current is passed through it momentarily, thus allowing ICs in the PSU to gauge how much current is passing through a given circuit.
These resistors are also typically metal-oxide flame-proof and fusible - that is, if overloaded severely, they will open like a fuse and will not burn down (something that regular carbon composition resistors may actually have trouble with.)

If you did measure them as 4 band they would still measure lower then spec
which leads to ask do i replace them with 4 band spec or 5 band spec resistors?

I suggest not to replace them, like R_J said. Indeed when resistors go bad, they don't go lower in resistance but always higher. The fact that they did not go open-circuit means they survived whatever fault there was in the PSU, again, since they are fusible type. I'm also a bit confused on their color band rating as well. The two with Black, Green, Silver, Gold, Green bands don't seem to fit any standard ratings, as black can't be a first color band (unless it's brown that has turned very dark - in which case, these should be 0.15 Ohm resistor, I think) and if rad the other way, Gold doesn't make sense as a 2nd color band either. The 3rd resistor also doesn't make sense to have a value starting with Blue (6) and Green (5) color bands, and the other way around has same issue as above with Gold as the 2nd band.

*EDIT*
According to the Digikey resistor calculator that Sam posted above, the resistors with color bands Black, Green, Silver, Gold, Green show up as 5.8 Ohms, 0.5%... and that's assuming the 3rd (middle) band is NOT actually Silver but rather Gray (calculator has no selection for Silver.)
And the other one (Blue, Green, Gray, Gold, Green) comes up as 65.8 Ohms.
...
Now that appears to be a match with your measurements in post #22, so I think they are OK indeed.

[sdinelli]

Re: 1300W PSU - Help with replacement mosfet

Thank you for your time and detailed explanation.
Ill order the stuff and see what happens.

[momaka]

Re: 1300W PSU - Help with replacement mosfet

Ill order the stuff and see what happens.

Sounds like a plan.

Oh and when you get to the part with testing with the series incandescent bulb, you may have to try a few things there. Namely, since this PSU has APFC, the APFC circuit may not function properly with the series bulb.

Thus, my suggestion is to first start with a 60-100 Watt bulb and see if the 5VSB comes up and also if the bulb stays off (after turning on for a moment on two when the PSU is first plugged in.) If 5VSB comes up, you can try to tun on the PSU by connecting PS-ON on the 24-pin ATX connector to ground. If the incandescent bulb blinks on and off for more than 2-3 seconds, you may have to use a bigger bulb (or two or three more bulbs in parallel with the first bulb.) This will increase the power the PSU can draw through the bulb(s) and thus may now allow the APFC to function properly and make the PSU run. However, if the bulb(s) stay fully lit after trying to turn on the PSU, there may still be a fault in the PSU. Do report back if you run into either of these two cases.

The series bulb tester is a very useful tool, but can also sometimes get tricky to use on PSUs with APFC and may make you think the PSU still has a fault when it hasn't. But in any case, it is still a good idea to use it, as without it you do run the risk of blowing your new MOSFETs again.

[sdinelli]

Re: 1300W PSU - Help with replacement mosfet

Well parts came in. PSU is all back together!
i really wish i had a solder sucker! getting solder out of the holes with just solder wick can be a pain.

Anyways
I just need to find a bulb socket.
basically i took an old power cord. cut the end and attached it to a typical electrical socket and wall box.
I removed a foot or so of shielding from the cord exposing the wires.
cut the black one, and plan is to attach them to the bulb socket and bam.

Sound about right??

[stj]

Re: 1300W PSU - Help with replacement mosfet

and bam.

the lamp is to prevent that!

[sdinelli]

Re: 1300W PSU - Help with replacement mosfet

Welp here it is, i guess im going to see if i get 5VSB

I if you all dont hear back then im probably in heaven or hell

[sdinelli]

Re: 1300W PSU - Help with replacement mosfet

i have 5VSB!

[stj]

Re: 1300W PSU - Help with replacement mosfet

that lamp looks surprisingly white, is it a real glass filament lamp??

[sdinelli]

Re: 1300W PSU - Help with replacement mosfet

welp. i guess its a failure.
i get the 5vSB but psu doesnt turn on.
testing a spare 350W psu with the limiter i get all my voltages.

Do you think the 1300W is too much for the limiter or something?
im using a 72W bulb and bulb turns on and fades quickly when switching psu on.

Any thoughts?

[sdinelli]

Re: 1300W PSU - Help with replacement mosfet

that lamp looks surprisingly white, is it a real glass filament lamp??

yes i believe it is a standard incandescent bulb. its just frosted glass i suppose

[sdinelli]

Re: 1300W PSU - Help with replacement mosfet

OK i did some testing with the supply switch on but pins not shorted.
my results are
150V across main filter caps.
150V on both source and gate on the two fets i replaced but nothing on the drain. I imaging the drain will only be present when PSU = on?

the two other fets i had highlighted in yellow in that picture:
Fet on right=
S & G = 150V
D= .45V or .55V depending on which side of main cap you use as ref

Fet on left:
S & G= .39V
D= 150V

Im not sure if these sound ok or not?
I'm not sure which part of the circuit switches it on i guess i can trace the psu -on pin and see where it goes....