FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

[sententia]

Hello,

I have this mini 250w PSU that comes from a MSI Hetis G31 barebone.

The problem started with lockups during windows login until the computer would not start at all. The PSU started but the power led from the motherboard was blinking.

I removed the psu and tested it. It switched on whith eratic voltages and shuted down after a bit. Upon inspecting the PSU all of the secondary capacitors were buldged so i replaced them all. All of them tested with zero capacity. Two of them where reported as diodes by the tester.

Now the computers switch on and seem to have good voltages however without load. If i connected a hard disk the PSU starts power cycling again. With out a hard disk i can boot windows from a a usb hard drive without problems. Also the is a small tickling sound coming from the psu. It was much louder before replacing the caps.

Any ideas what to look next?

[sententia]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

The removed teapo 4x 3300uf 10v , 1x 4700uf 16v. Replacements Hitano for the 16v and Sanyo wx for the 10v.

[c_hegge]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

I think that Sanyo WX you've got there is a fake. It should have a K-shaped vent, not a Y.

It's probably not causing your problem at this point, though. I would try replacing all of the other caps, except for the primaries. Replace even the small ones with no vent stamps.

[sententia]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

I think that Sanyo WX you've got there is a fake. It should have a K-shaped vent, not a Y.

It's probably not causing your problem at this point, though. I would try replacing all of the other caps, except for the primaries. Replace even the small ones with no vent stamps.

No actually it doesn't work! As soon as i add one hard drive the computer does the same thing. PSU and cpu fan on, but power led blinking...

I know about the sanyo capacitors.... Also the thermal plastic on them looks sluggish as well.... Anyway they measure OK! Thanks for the tip..

[sententia]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

I have tested the marked capacitors.

All tested ok. The one on the right blue circle , is 1000uf and had about 940uf but is still within the +- 20%. Also it doesn't connect to 5v or 12v rails which i think are the suspect....

The ones on the primary side red mark are 2.2uf 50v and had about 8ohms esr, however some other 2.2uf 100v i have give me about 5ohms...

The 2.2uf are OST RLS capacitors. According to datasheet they should have 0.34ohms at 100khz but i don't know at what frequency my tester works....

[ben7]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

I have tested the marked capacitors.

All tested ok. The one on the right blue circle , is 1000uf and had about 940uf but is still within the +- 20%. Also it doesn't connect to 5v or 12v rails which i think are the suspect....

The ones on the primary side red mark are 2.2uf 50v and had about 8ohms esr, however some other 2.2uf 100v i have give me about 5ohms...

The 2.2uf are OST RLS capacitors. According to datasheet they should have 0.34ohms at 100khz but i don't know at what frequency my tester works....

I'd say the OST capacitors are bad.
Hitano and OST capacitors are of dubious quality :S

[sententia]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

I'd say the OST capacitors are bad.
Hitano and OST capacitors are of dubious quality :S

I replaced the OST 2.2uf with some Lelon i had but no change...
Power cycling and tickling sound mathcing the blinking of power led...

However the OST are low ESR caps compared to Lelon which are standard. From my tester i get about 9ohms from OST and 4-5ohms from Lelons...

I don't understand their purpose there... I tested them because they are near the MOSFETs so their were getting a lot of heat.

Do you think they could be the suspect for the problem?

[ben7]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

I replaced the OST 2.2uf with some Lelon i had but no change...
Power cycling and tickling sound mathcing the blinking of power led...

However the OST are low ESR caps compared to Lelon which are standard. From my tester i get about 9ohms from OST and 4-5ohms from Lelons...

I don't understand their purpose there... I tested them because they are near the MOSFETs so their were getting a lot of heat.

Do you think they could be the suspect for the problem?

Yeah those OST are bad.

But, really, have you check ALL electrolytic capacitors, the little ones on the daughterboards, etc...?

[sententia]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

Ben it will be very time consuming to test all the electrolytics as some of the daugherboards have about 20 pins and will be a pain to remove. I am trying to pinpoint the problem rather that randomly testing components. I have tested some capacitors around the PSU and all look ok except those 2.2uf on the primary. They connect to the small transformers if that helps...


Also i don't know where the tickling crimping sound comes from..

Also i noticed that not many brands offer 2.2uf low ESR and are a bit difficult to find.

I have some more pics of the fake looking SANYO WG compared to other WX which have the K on top...

P.S. Some more input on the daugherboards.

1. Has the fan and temperature sensor on it and i suppose it is that fan control cirtuit

2. Has the WT7518D which is a "Power supply supervisor" with OVP and output monitoring

3. I can not make the IC... just the 3528 that is shown in the photo

[sententia]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

I tested the PWR_OK cable ( i should have done this earlier) and when the power cycling happens the PWR_OK voltage fluctuates from 0.5v to 2.5v.

If i remove the fans for example the and pc switches on the PWR_OK goes to 5V

[sententia]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

Yeah those OST are bad.

But, really, have you check ALL electrolytic capacitors, the little ones on the daughterboards, etc...?

I checked where PWR_OK cable and it connects to the big daugherboard with the 3528 ic. I had to remove the pcb to check the parts. On the main board it says PWM circuit. I tested all parts and i decided to replace two little capacitors. the 2.2uf had 18ohms esr and the 1uf had about 0.91uf capacitance and good esr.

I also installed the original OST on the primary side.

The PSU now works without any problems! I have been stress testing the computer for couple of hours and everything looks good until now.

Thanks ben for suggesting to check all little capacitors....

[Th3_uN1Qu3]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

Good job. It can be a huge pain in the behind to narrow down the problem to a couple little electrolytics, so i usually replace them on sight when they're around control circuits. Saves time.

[ben7]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

Good job. It can be a huge pain in the behind to narrow down the problem to a couple little electrolytics, so i usually replace them on sight when they're around control circuits. Saves time.

I totally agree with that one!

I checked where PWR_OK cable and it connects to the big daugherboard with the 3528 ic. I had to remove the pcb to check the parts. On the main board it says PWM circuit. I tested all parts and i decided to replace two little capacitors. the 2.2uf had 18ohms esr and the 1uf had about 0.91uf capacitance and good esr.

I also installed the original OST on the primary side.

The PSU now works without any problems! I have been stress testing the computer for couple of hours and everything looks good until now.

Thanks ben for suggesting to check all little capacitors....

Glad you got it fixed!
Honestly, you should take the OST on the primary side back out. Their ESR readings seem a bit high...

[sententia]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

I know i should replace the OST ones in the primary side however i still cannot find any capacitors matching the ESR of OST RLS (0.34Ω !?)! It almost looks like a typo as all other brands (so far i have checked Nichicon, Rubycon and Panasonic) offer low esr caps at 1.8ohms to 4ohms (for 2.2uf).... Do you think i should replace them with just any low esr cap?

To be honest at the start i didn't think a small cap would be the problem (i am talking for the ones replaced) but i had to check the daughterboard because of PWR_OK signal. I will be more thorough next time

Thanks for the help

[Th3_uN1Qu3]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

They're likely lying. 2.2uF caps have an ESR of at least 1 ohm.

[tmiha71]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

standard caps ESR values...

http://elektrotanya.com/?q=hu/conten...kek-esr-values

If those OST-s were in circuit to drive base of switching transistors, you can use 4.7uF, or even 10uF (same voltage), a lot of PSU-s use 10uF...

[ben7]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

Yeah, use some 4.7uF or 10uF capacitors instead.

The thing is, even a good low-ESR capacitor of 2.2uF has an ESR of a few ohms. Those OST caps, which are supposedly low ESR, measure about 8 ohms ESR from you measurments. Either way, they are bad, and being in that hot location means they will go bad quicker.

[sententia]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

I understand that their ESR is bad as i got 4 to 5 ohms from the standard Lelon 2.2uf 100v RGA that i had...

I don't have the knowledge to find their purpose there but i thought if they were there to create some kind of oscillation it would change by altering their capacitance...

Anyway i have marked the location of them on the PCB if that helps anyone if its safe to replace with bigger ones ... They are definitely between the MOSFETS and the two small transformers..

[Th3_uN1Qu3]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

Those are no MOSFETs. It's the classic half-bridge with BJTs. Those caps serve the purpose of "acceleration" of turn-on, they create a current spike in the BJTs' bases on every switching cycle. Along with the (usually 1N4148) diode and resistor, they form a waveshaping circuit.

Anywhere between 2.2uF and 22uF is acceptable there, efficiency of the PSU mays slightly vary depending on their exact value, but it's by no means critical. They rarely fail in that position unless the switching devices fail, so you can keep them there.

[sententia]

Re: FSP250-50MSP PSU from MSI Hetis G31 Barebone 250W

Those are no MOSFETs. It's the classic half-bridge with BJTs. Those caps serve the purpose of "acceleration" of turn-on, they create a current spike in the BJTs' bases on every switching cycle. Along with the (usually 1N4148) diode and resistor, they form a waveshaping circuit.

Anywhere between 2.2uF and 22uF is acceptable there, efficiency of the PSU mays slightly vary depending on their exact value, but it's by no means critical. They rarely fail in that position unless the switching devices fail, so you can keep them there.

Thanks for the detailed info! I might as well leave as it is... it has been running ok from yesterday, and i have everything in the box. Anyway i have access to the pc so i can replace them anytime.