Ultra Xfinity 600w 5vsb mod

[c_hegge]

Re: Ultra Xfinity 600w 5vsb mod

Cool. Now you owe me the power supply. After all I did help you fix it Just kidding

Try it with some load. I had the same issue with those Widetech/Great Wall power supplies. They had a slight squeal with no load, but they were fine as long as I loaded the 5vsb and 12V rails, it was fine.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

Either it doesn't agree with one of the capacitors, you shorted two traces, or you have a cold joint. I had this when I was re-building the rexpower and it took me a few days to spot the solder bridge, as it was only very small.

DING DING DING!

found some solder bridges on the primary side. fixed, and aside from the screeching (me thinks its a no load issue?), it works.



then again, i was rushing thgere, as the superglue used on the loose traces was vaporizing from the heat, and i did't want to pass out or the like. that, and it made my nose burn.

chegge,

I owe you...

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

Either it doesn't agree with one of the capacitors, you shorted two traces, or you have a cold joint. I had this when I was re-building the rexpower and it took me a few days to spot the solder bridge, as it was only very small.

noted- I'll check.

only values chaned is the 2 5vsb caps are 10v 1000uf, as opposed to the stock 16v 680uf.

[c_hegge]

Re: Ultra Xfinity 600w 5vsb mod

Either it doesn't agree with one of the capacitors, you shorted two traces, or you have a cold joint. I had this when I was re-building the rexpower and it took me a few days to spot the solder bridge, as it was only very small.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

any ideas on what could have killed it?

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

Wait, wasn't this PSU working before??

minus some bad screeching, yes

i know that the guts were squished a bit after the recap... the new caps were physically larger than the stock caps.



i don't know what to say here...

[momaka]

Re: Ultra Xfinity 600w 5vsb mod

Wait, wasn't this PSU working before??

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod





she's dead.

recapped it, was a very tight fit,

still makes the dreaded acing like noise it made before. 5vsb is in spec.

gave it the power on signal (green to gnd), no change. 0v on everythign but 5vsb.



now to find a 400W+ psu for the project box this was for... (my biggest is a 300W delta)

[c_hegge]

Re: Ultra Xfinity 600w 5vsb mod

If the PSU has had a few years of use, then my general rule of thumb is that if they are discolouring the PCB, then replace them, otherwise, they are fine.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

there were no obvious signs of heat damage... not that i could see anyway. it is a black pcb, but all the silkscreening was pearly white.

will check when I get a chance

[momaka]

Re: Ultra Xfinity 600w 5vsb mod

uhh the order is already on it's way to my house... all i grabbed was a 1W 100 ohm resistor...

That's fine. Just check what they are anyways. Some are just better off removed completely rather than replaced. Older Deer and Allied PSUs, for example, like to put 100 Ohm 2W resistors on the 12v rail - that's 1.44W of heat, which is quite considerable (enough to darken the PCB board and cook caps). I remove those on sight and just replace them with whatever I find in my junk box - usually 2x 1000 Ohm 1/2W in parallel.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

Not exactly.
This is a half-bridge design - PWM controller is on the secondary side, not the primary, so there are no start-up capacitors for the main PSU section.

What these caps do is they filter the pulses from the driving transformer that turn on the BJTs. They aren't exactly super-critical or anything, so technically they don't *need* to be replaced, but it's a good idea since if the old ones are going bad, the efficiency of the PSU will also become worse. And worse efficiency = more heat inside the PSU.

As for the 100 Ohm resistor, the 1/2W rating wouldn't have been so bad if it was a little further from the 5vsb filter caps. But because it isn't, a 1W resistor would be better since it is bigger and will run cooler. You don't need any heatsinks or anything like that. A 100 Ohm resistor on the 5vsb is only dissipating V*V/R or (5*5)/100 = 0.25 watts, which is not that much at all. It's only half of what your current resistor is rated for.

Which reminds me... check if there are any large loading resistors on the 3.3v, 5v, and 12v rails.

uhh the order is already on it's way to my house... all i grabbed was a 1W 100 ohm resistor...

I am less concerned about the other rails, as this PSU is a twin fan setup and those railsare only active when the fan is on... unlike the 5vsb, those rails always are being activly cooled when activated.

[momaka]

Re: Ultra Xfinity 600w 5vsb mod

I believe those two caps are the start caps for the switching transistors.

Not exactly.
This is a half-bridge design - PWM controller is on the secondary side, not the primary, so there are no start-up capacitors for the main PSU section.

What these caps do is they filter the pulses from the driving transformer that turn on the BJTs. They aren't exactly super-critical or anything, so technically they don't *need* to be replaced, but it's a good idea since if the old ones are going bad, the efficiency of the PSU will also become worse. And worse efficiency = more heat inside the PSU.

As for the 100 Ohm resistor, the 1/2W rating wouldn't have been so bad if it was a little further from the 5vsb filter caps. But because it isn't, a 1W resistor would be better since it is bigger and will run cooler. You don't need any heatsinks or anything like that. A 100 Ohm resistor on the 5vsb is only dissipating V*V/R or (5*5)/100 = 0.25 watts, which is not that much at all. It's only half of what your current resistor is rated for.

Which reminds me... check if there are any large loading resistors on the 3.3v, 5v, and 12v rails.

[Rulycat]

Re: Ultra Xfinity 600w 5vsb mod

parts ordered.

Great. Let us know how you get on with it.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

parts ordered.

[mockingbird]

Re: Ultra Xfinity 600w 5vsb mod

Yea, I'm going with Newark this time around because I need some other stuff that only they have. I'm also about to order very soon, probably tomorrow.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

mouser.

(technically, not ordered yet, but will be very soon).

[mockingbird]

Re: Ultra Xfinity 600w 5vsb mod

Where did you order from?

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

order placed.

hope this all works out...

[c_hegge]

Re: Ultra Xfinity 600w 5vsb mod

I am correct that I should replace the tiny 1/2W 100 ohm load resistor with a 1W equivlant? (I included it in the order). I am also wondering if there is a way to place a heat sink on the resistor?

Yes. If you can find a heat sink that won't interfere with anything else, then you can use some thermal epoxy to attach it to the resistor (although be careful not to get it on the legs as it is conductive). Another thing I have done before is solder it onto some wires and attach it to the secondary heat sink with thermal epoxy.