Repairing Sparkle 235W with bad rails?

Hi guys,

I inherited a PII rig today with a bad PSU. It's a Sparkle 235W, not the meanest thing around, but I could really use it to get my dualie setup running.

At first I thought it was just overheating because there was about 3 inches of black dust and dirt caked in it. I cleaned it out really, really well and while I got it running the rails are totally skewed. +12V is running at 9.84V, and +5V is at 5.83V. Tested this with a digital multimeter so they should be pretty accurate.

I don't have any experience trying to fix these things, and I don't know if it's even remotely practical. Any ideas on whether I can revive this sucker? I don't see any physical damage inside, and aside from the dust it looks pretty new. I know I could probably pick one up for dirt cheap but that's not the point

Thanks

Heh, I just ordered a generic refurb 300W from Newegg for $10 shipped! Still want to fix this one though, as I need two or three to get all my spare rigs running. Gotta fold!

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Originally posted by Tekime
Hi guys,

I inherited a PII rig today with a bad PSU. It's a Sparkle 235W, not the meanest thing around, but I could really use it to get my dualie setup running.

At first I thought it was just overheating because there was about 3 inches of black dust and dirt caked in it. I cleaned it out really, really well and while I got it running the rails are totally skewed. +12V is running at 9.84V, and +5V is at 5.83V. Tested this with a digital multimeter so they should be pretty accurate.

I don't have any experience trying to fix these things, and I don't know if it's even remotely practical. Any ideas on whether I can revive this sucker? I don't see any physical damage inside, and aside from the dust it looks pretty new. I know I could probably pick one up for dirt cheap but that's not the point

Thanks

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how much do you know of electronics?

is the input fuse blown?
if so, and theres no obvious damage, it is likely a diode in the incoming power area, part of a rectifier circuit for the incoming AC..

you can find a replacement in vcr/dvd power supplies or even an old AT will have one..

they mightve even used a bridged-diode asm.

A complete waste of your time as evidenced by your $10 300W supply. Don't bother.

LordOPain: Thanks for the info. I don't know a heck of a lot about electronics, but I want to learn! I learn things by doing them, and I'm willing to research and take my time with it. Am I an idiot for trying to troubleshoot this thing? Can you point me to some links that might help out with some details on what you mentioned? Also do you know how to discharge a PSU? Don't feel like getting fried :) I'll read up on the things you mentioned, I don't have a lot of electronics experience but I think I can catch on fairly quick unless it's really, really complicated.

Adisharr: I was fully expecting that response from someone :) I'm more interested in doing it than just having the PSU I think... so I see where you're coming from but I think it would be fun to try and fix this basterd, and if I actually get it working It'd feel pretty good :)

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Originally posted by Tekime
LordOPain: Thanks for the info. I don't know a heck of a lot about electronics, but I want to learn! I learn things by doing them, and I'm willing to research and take my time with it. Am I an idiot for trying to troubleshoot this thing? Can you point me to some links that might help out with some details on what you mentioned? Also do you know how to discharge a PSU? Don't feel like getting fried :) I'll read up on the things you mentioned, I don't have a lot of electronics experience but I think I can catch on fairly quick unless it's really, really complicated.

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iz gonna take sum splaynin loozy..

but, itll come in handy when someone says"i have this older packard Bell/Aptiva/Gateway/Dell/etc. etc. and it has this 185watt or 200watt power supply that doesnt work and I cant find one that size(physical size)anywhere" or "crap its friday night, i was gonna go to a LAN party but..."

unless theres a black spot they usually arent that bad and if its only $time$ out of pocket, then what the hay..;)

in a switching power supply, the AC power will typically come into the box and go to a fuse..

then itll get some filtering(possibly some capacitors and inductors/chokes)

itll then be turned to high voltage DC(usually 170v or close to it) by means of a rectifier(a diode, set of diodes or a diode asm called a bridge).. ** this is where your failure may be..

that then goes across a large capacitor or 2, this is the stored energy that you were asking about.. the best way is to bleed it off with resistors, but in a pinch an old screwdriver across the pins works..

the high voltage DC then gets routed to the "FET circuit" where its pulsed across the transformer by turning the FET(s) ON the OFF at a high rate of speed..

thats some to chew on.. keep in mind that as of many recent advancements in PSU's, there may be many components added.. things like Powre Factor Correction and whats being called "3 and 4 phase" control..
so keep that in mind when your looking at the parts..

youll need a meter capable of reading ohms up to 100000 or 100K..

good luck

Ahh, good stuff :) I'll digest this when I can get home and crack it open again. The only resistors I have are really small, so I don't know if they'll cut it or not. I'll try the screwdriver thing. If you don't hear back from me, I'm dead :D

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Originally posted by Tekime

Adisharr: I was fully expecting that response from someone :) I'm more interested in doing it than just having the PSU I think... so I see where you're coming from but I think it would be fun to try and fix this basterd, and if I actually get it working It'd feel pretty good :) [/B]

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I commend you for investigating.. It's even better if you can learn something from it and not get killed.. I specialize in absorbing shocks myself :D

Haha :) Hey this could be your claim to fame :)

Adisharr!! Human Resistor!! See him absoooorb!!

LordOPain, I opened it up again last night and tried to follow everything you named off. Everything looks pretty similar to what you said, power goes into the PSU, through a switch, to a fuse, then a bunch of inductors/chokes, and I see a big rectifier right next to the two large capacitors. There's a little black stuff on two of the legs, but its spotty and I think it might just be dust (the thing was caked). Hard to tell since it's pretty crowded and I don't want to touch it until it's discharged.

About discharging the capacitors, I can't get at the the pins on it since the PCB is screwed down and I can't see the bottom side yet. Should I unscrew that and flip it over, then short the two solder points on each capacitor? Will any old screwdriver work? And will I risk damaging the PSU even more this way? I'll try the resistor method if you can tell me what kind of resistor would work and how to go about connecting it without getting fried.

Sorry for all the questions, but I haven't done this before and I don't feel like getting fried. Watched some videos of people blowing things up with capacitors last night and those things pack a punch :eek:

Tekime, you have some cajones to be messing around with a PSU like this. Good luck.

i remember in electronics in high school we would carge Small caps and toss to some idiot a say here catch this :D :eek:

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Originally posted by Tekime
LordOPain, I opened it up again last night and tried to follow everything you named off. Everything looks pretty similar to what you said, power goes into the PSU, through a switch, to a fuse, then a bunch of inductors/chokes, and I see a big rectifier right next to the two large capacitors. There's a little black stuff on two of the legs, but its spotty and I think it might just be dust (the thing was caked). Hard to tell since it's pretty crowded and I don't want to touch it until it's discharged.

About discharging the capacitors, I can't get at the the pins on it since the PCB is screwed down and I can't see the bottom side yet. Should I unscrew that and flip it over, then short the two solder points on each capacitor? Will any old screwdriver work? And will I risk damaging the PSU even more this way? I'll try the resistor method if you can tell me what kind of resistor would work and how to go about connecting it without getting fried.

Sorry for all the questions, but I haven't done this before and I don't feel like getting fried. Watched some videos of people blowing things up with capacitors last night and those things pack a punch :eek:

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it shouldnt be that bad.. considering that youve had it off for a day or so.. it should only be 1 or 2 large capacitors that you need to even be concerned with. if its not plugged in, its certainly not gonna kill you.. might get a bite though..

was the fuse ok? you can measure ohms on it and it should be less than 1 ohm.

there will usually be 4 screws, then lift up enough to get to the pins of the caps.

how many legs on the rectifier? should be 4 for a bridge package..
there will be a + or perhaps a notch on one corner..

if its seperate diodes, there will be 2 or more and theyll usually be black with a silver band..

none of the diodes or diode bridges should read "shorted" or zero ohms.

scout around for an old VCR or DVD player.. anything with a power supply that could be scavenged..

be careful playing with psu's, from what i've read it's pretty dangerous to crack one open if you don't know what you are doing. You can get electricuted.

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Originally posted by LordOPain
it shouldnt be that bad.. considering that youve had it off for a day or so.. it should only be 1 or 2 large capacitors that you need to even be concerned with. if its not plugged in, its certainly not gonna kill you.. might get a bite though..

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Ahh, well it's good to know death isn't a factor then :)

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was the fuse ok? you can measure ohms on it and it should be less than 1 ohm.

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Well, if I did it right it was 0.0 - 0.2 Ohms. I popped out the fuse and put the leads right on each end. It seemed to jump around a lot though, at first it would fly around anywhere from 20-50 Ohms but then gradually drop back down to < 1.0 Ohm.

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there will usually be 4 screws, then lift up enough to get to the pins of the caps.

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Yup, one screw in each corner.

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how many legs on the rectifier? should be 4 for a bridge package..
there will be a + or perhaps a notch on one corner..

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4 legs, it's one big black package itself. No + symbol but one end of it is notched.

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none of the diodes or diode bridges should read "shorted" or zero ohms.

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So just set to ohms and/or continuity test?

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scout around for an old VCR or DVD player.. anything with a power supply that could be scavenged..

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Hrm... well I'll test it out first but I just tossed a bunch of old stuff when I moved :mad: I've got an old AT PSU I can tear apart though. Maybe some other stuff, I'll look around!

Many, many thanks for all your help on this!