Sansun SN-W450 ATX - buzzing & burn marks

[quattro alex]

Model:Sunsung "make your life beautiful" SN-W450 ATX
Sticker: 0604 005 263

Fault: Buzzing heard with the psu powered on without load. Probably still buzzing with load but intake fan too noisy to hear.

Background: Work colleague asked me to take a look at this psu which he has had for a few years, he mentioned the buzzing and the fact it looked quite dusty - this was an understatement.

Testing / observations:

PSU (cheap tester) showed the following rail voltages:
+3.3 = 3.3v
+5 = 5.2v
+12v1 = 12.1v
+12v2 = 12.1v
-12v = 11.6v
5vsb = 5.1
PSG=280ms (not sure what this means)

Once I'd removed a lot of the dust I saw that caps C19 & C20 were bulging. These are JEE caps with a value of 2200UF and 10 volts. Tested values were ESR of 2.2 & 2.3, no capacitance value available - I am assuming it was too low. I still have to measure a few of the other caps (Canicon and Su'Scon)

At this stage I had a sniff and I could smell that burnt plastic smell. I unscrewed the secondary board which sat upside down above the 2 large black caps. This didn't look so good - the pcb was very discoloured around 2 resisters. I need some help trying to work out the values of these resisters as the colour bands are badly burnt. There is also no continuity on either of the resisters.

I will carry on testing the remaining resisters that I can work the values out on. The general layout on this psu seems quite poor and everything seems very tightly squeezed in. Add copious amounts of dust and this can't make for a long service life.

Photo's to follow shortly.

[quattro alex]

Re: Sansun SN-W450 ATX - buzzing & burn marks

photo's now attached

[everell]

Re: Sansun SN-W450 ATX - buzzing & burn marks

Does the fan blade spin freely? If not, a good place to start would be to take the fan apart, clean and oil the bushing, then reassemble. Without a freely spinning fan, I would expect lots of continuing heat problems.

[c_hegge]

Re: Sansun SN-W450 ATX - buzzing & burn marks

Those resistors won't get much airflow, even with a working fan. I think that the best solution would be to disable the APFC and remove the PBC (although I don't know if that's legal in the UK, since PFC is mandatory there). As for the buzzing, it's probably the two big caps going bad. JEE are a notoriously unreliable brand and APFC puts more stress on them than usual.

[Th3_uN1Qu3]

Re: Sansun SN-W450 ATX - buzzing & burn marks

Those resistors won't get much airflow, even with a working fan. I think that the best solution would be to disable the APFC

Or use resistors with proper power rating.

[b700029]

Re: Sansun SN-W450 ATX - buzzing & burn marks

280ms is the time from power-on to when the Power Good signal comes up.

It looks a lot better than some "500W" gutless wonder, and some of the newer high-wattage PSUs are just as cramped inside. Poor choice of caps though.

For figuring out the value of the resistors you can pull the endcaps off and try measuring the resistance across the carbon spiral directly. They might not be directly responsible, but something else failed in the APFC circuit may have caused them to overheat.

[tom66]

Re: Sansun SN-W450 ATX - buzzing & burn marks

The buzzing could be bad primary caps. I had a PSU that did that when the primary caps were bad - then again, they were only fake 330uF ones (actually 220uF.)

[quattro alex]

Re: Sansun SN-W450 ATX - buzzing & burn marks

The fan spins, but could definitely be smoother, so I will take it apart and use something like lubricating oil for a shredder.

Big JEE 85c (CE.W IM0610) caps are rated at 820uf and 200v - tested at no1. 840uf & 0.17 esr. No2.770uf & 0.20 esr - I haven't got these, what would be a good replacement and what level of ripple should I be aiming for?

I got a reading for both resisters using the 200K scale on my DMM. 1.374 & 1.376 - can you recommend which value I should replace these with?

APFC - does this stand for automatic power filtering control? I don't know about the regulations regarding this, and I am not sure I'd feel comfortable removing it - especially as this is not my equipment.

Thank you for all the advice / suggestions so far.

[mcdaydavies]

Re: Sansun SN-W450 ATX - buzzing & burn marks

I think APFC means active power factor correction.

[PeteS in CA]

Re: Sansun SN-W450 ATX - buzzing & burn marks

That's what it is, mcday. Without power factor correction (PFC) the voltage charge on big input lytics mean that the P/S only draws current from the AC line during the very brief parts of the 50Hz or 60Hz sine when the voltage at the input is higher than the voltage across the caps. If you saw the input current on an oscilloscope you would see alternating, brief, high amplitude, positive- and negative-going spikes with relatively long periods between during which little or no current flows. Ideally, PFC allows current to flow throughout the sine wave cycle, in phase with the voltage, with sinusoidal amplitude.

Active PFC comes close to achieving that ideal, but requires and extra controller (or a dual controller), an extra switch device, an extra rectifier, and an extra inductor. Passive PFC doesn't come as close to the ideal, but is much simpler - a large, heavy, steel laminations core inductor between the bridge rectifier and the input lytics. Active PFC is usually wide range, capable of operating from 120VAC (nominal) or 240VAC (nominal) without setting a voltage range switch. A P/S with Passive PFC requires a range switch.

[b700029]

Re: Sansun SN-W450 ATX - buzzing & burn marks

The primary caps are within tolerance. They're usually +/- 20% so 820uF could mean anywhere from 656 to 984uF. They are probably JEE LM series ( http://www.jee-jee.com/huizhou/digit...id=1437&bb=eng ) although their catalog indicates they should be violet and not black.

The resistors might be 137K.

[c_hegge]

Re: Sansun SN-W450 ATX - buzzing & burn marks

^
The capacitance is probably OK, but the ESR seems a bit high

Or use resistors with proper power rating.

The burned resistors look to be fairly beefy, so unless you go with larger power resistors, higher wattage ones may not be available.

[quattro alex]

Re: Sansun SN-W450 ATX - buzzing & burn marks

My colleague is looking to keep the cost down so I'll hold fire on replacing the primary caps for the moment. With regard to the resistors is it likely that their resistance has decreased or increased over time?

I am concerning about getting the correct wattage. When I look online the 137k 0.25w resistors don't look beefy enough. The measurements of the resistors are 11.1mm long by 3.5mm diameter, lead wire of 0.74mm. Is it likely that these would be 2w or higher in rating?

Is something like this suitable? http://uk.rs-online.com/web/p/throug...fixed/2142235/

[Th3_uN1Qu3]

Re: Sansun SN-W450 ATX - buzzing & burn marks

They are likely to be over 1W, i think 3W ones will fit.

[quattro alex]

Re: Sansun SN-W450 ATX - buzzing & burn marks

What are the risks of going with a higher wattage?

[Th3_uN1Qu3]

Re: Sansun SN-W450 ATX - buzzing & burn marks

Risk of going with higher wattage: Might not fit due to larger physical dimensions.
Risk of going with lower wattage: Suffer the same fate as the original ones (burn out).

[Behemot]

Re: Sansun SN-W450 ATX - buzzing & burn marks

As for the APFC, I got some dealing with our business inspection (basicly tried to get them ban some crappy PSU, it is just fine according to them - they must be corrupted) and learned that no standard defines use of PFC in EU. There are only restriction for backward harmonic emissions, but I think that could be mostly get rid of by proper filtration. The PFC is just easy way to do that, and as for higher power-rated PSU's, you have to use APFC to not blow of your breakers all the time (cause you get higher current consumption without PFC).

As for the resistors, what about doing some flymod or attaching them to heatsink? :-)

[c_hegge]

Re: Sansun SN-W450 ATX - buzzing & burn marks

I think 3W ones will fit.

They may fit, but the ones in there look like 3W, so they will just do exactly the same thing.

If I wasn't going to disable APFC, I would use some 10W wire-wound resistors, use some Thermal Epoxy to stick them to a heat sink (assuming the PSU has one which isn't live) and use wires to connect them to the PCB.

[Th3_uN1Qu3]

Re: Sansun SN-W450 ATX - buzzing & burn marks

10W resistors are huge... 5W will do.

[c_hegge]

Re: Sansun SN-W450 ATX - buzzing & burn marks

^ Maybe, but it's still too close to the original 3W rating. If you're attaching them with wires, size is no big deal. There's room for a pair of 10W resistors there on the APFC heat sink. I used a few for the 5vsb and 12V rails on my load tester. I didn't think they were that big.