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fixing power supplies?

post #1 of 4
Thread Starter 
hi guys, I have had a bad time with psu's the past few months? my saber 990fx & FX8120 has blown 3 psu's, the symptoms is always the same motherboard lights on but the 8 pin cpu cable not working,
it always happens when turning off the system & then trying to turn it back on later? ive just sold the saber & fx cause im sick of the damn thing lol, I don't understand why it keeps happening? its plugged into a surge protected extension aswell?

do you guys know whether replacing the internal fuse will make the 2 dead ones I have work again? they are soldered aswell or are they totally borked, no capacitors or anything look burnt either?

thought id ask here & see if anybody knows about fixing psu's?

the fuse is a t6.3 10A 250v as far as I could see, ill have to look again to be certain though.

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post #2 of 4
Get another fuse with the same or lower amp rating and the same voltage rating (probably 250V). It's probably a slow-blow, but it's OK to use a fast-blow, and when in doubt, use a fast-blow.

You should be able to install a fuse holder on the circuit board. If the original fuse sat flat against the circuit board, this one will work:

http://www.tantiaelectronics.com/images/Fuse-Holders-&-Fuses/Mini-Fuse-Holder-PCB-Type-New-(5X20mm)-VKY-624.jpg

For vertically mounted fuses, try this:

http://www.alliedelec.com/images/products/Small/70149527.jpg

You probably need something made for a 15mm long fuse. Be sure the fuse holder is rated for at least 250V because some are made only for 32V or less.

If the replacement fuse blows, there's a short somewhere else, almost always in the high voltage section, meaning either the power factor correction transistor or the inverter transistors. You don't need exactly the same part numbers for replacements, but the characteristics have to be similar, i.e., if the power factor corrector transistor is an insulated gate bipolar, the replacement can't be a MOSFET. Also ratings for amps, power and voltage have to be at least as high, the frequency rating similar, and for MOSFETs the gate capacitance about the same. It's best to get recommendations at a place like sci.electronics.repair or BadCaps.net. Also be careful about the packaging type because that determines how the new transistor has to be electrically insulated from the heatsink. Some packages are completely insulated, others require a silicone rubber insulator sheet, and some also need a nylon shoulder washer for the mounting screw. If you get the insulation wrong, the new transistor will instantly burn out. Some PSUs have thermal paste on their insulators, others have nothing, but if you decide to apply paste, be sure it's dielectric, not anything like Arctic Silver. Radio Shack Transistor Heatsink Grease is fine, as is dielectric grease sold by auto parts supplies. Another thing: access to the transistors is usually tight, meaning you can rarely can you simply remove just the bad transistors. Instead you usually need to unsolder all the parts mounted on the heatsink, including the heatsink's solder lugs, and take out the whole assembly. Transistors can usually be tested with just a multimeter's ohms or diode check function.
Do NOT apply power to the repaired PSU except with everything reinstalled in the PSU case and the case cover screwed back on completely because a big capacitor could explode, and you don't want to get a shock from one of the big heatsinks, which are often connected directly to high voltage. I once failed to do tha with an old Antec, and when I plugged the AC cord into the case, it flexed enough to touch a big heatsink, causing an arc and made the PSU shut down.
Edited by larymoencurly - 8/28/13 at 4:29pm
post #3 of 4
Thread Starter 
hi thx for the reply smile.gif

ive found its a 6.3mm x 35mm 10A 250v slow blow fuse that's needed, also ive been reading around a little & it could be numerous other parts such as the diodes,caps etc before the transformer thing usually? still researching about it tbh

I think im just gonna try the fuse's & see how it goes tbh, I didn't hear any pops/no burnt smell or anything so I think its the fuse, haven't got a multi meter or anything to test so im just taking a long shot with it lol.

got a couple of soldering irons & stuff though so hey might aswell give it a go?

thx for the safety advice aswell, im well aware of the dangers of electricity lol, ive had a fair few shocks in the past, couple of bad ones aswell when I was young! true arc shocks that blew me across the room biggrin.gif

im not that naïve now, when it comes to messing with electronics lol!
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The Hot Minion
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CPUMotherboardGraphicsRAM
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Hard DriveOptical DriveCoolingCooling
2x Corsair force 3 120GB pioneer dvdrw/bdrw XSPC Raystorm EK Coolstream 360  
CoolingCoolingCoolingOS
EK Coolstream 240 Alphacool D5 with HF Top 2x EK 7990 SE alcatel/nickel blocks Win7 ultimate 
MonitorKeyboardPowerCase
24'' AOC 1080p x3 + 42'' LG 3DTV saitek eclipse enermax revolution 1050w nzxt switch 810 
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i7 4790k 4.7ghz MSI Z87 GD65  3x XFX R9 280x GSKILL 16GB DDR3  
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Hard DriveOptical DriveCoolingOS
2x 120gb mushkin chronus SAMSUNG DVDRW EK SUPREME HF+ 360+240 rad win7 ultimate 
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3x aoc's through kvm's CORSAIR TX850M RC1000 COSMOS 
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post #4 of 4
Sometimes old fuses just go, and I hope that's the case here, but I can't be optimistic. You may want to check for shorts caused by bad soldering or wire leads that weren't cut short enough. I once restored a dead PSU by bending up a wire lead that was touching an adjacent copper trace, but no fuse was blown.

The cheapest multimeter is more than good enough to diagnose the components (with the AC cord unplugged), but for the price, digital ones are a lot better than analog ones.

Good luck.
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