Antec TruePower 380p failed after intermittent supply, suspect MOV

[rabbituk]

Hello,

I have an Antec TruePower 380p PSU that I had repurposed from a Sonata case. It had been working fine on a server in the loft using the Wake-on-LAN feature regularly until a couple of recent power outages where the power became very unstable - going on/off very quickly. There is now no output whatsoever from the PSU & fan isn't working. There was a pop when I attempted to turn it on.

Upon examination, it appears that voltage isn't getting very far so I believe the immediate issue is within the first stage. There is a green component that I am not familiar with. It has '005 10' written on it. Is it a MOV? Does anybody have an idea of the spec? There is a hairline crack that goes around the side of it and a burn mark on the rear. So I'm guessing this means it is toast. The DMM measures 22Ohm.

Here are some photos...
Front of component
Rear of component

Any help in suggesting a replacement MOV appreciated - assuming I'm correct that it is a MOV!

Daniel

[stj]

Re: Antec TruePower 380p failed after intermittent supply, suspect MOV

not a mov.
mov's are smooth and will meter open-circuit when good.

that rough surface part is an inrush limiting resistor that lowers it's resistance as it heats up.
it's probably fine as it isnt split in half or a pile of ash!

[rabbituk]

Re: Antec TruePower 380p failed after intermittent supply, suspect MOV

Thanks for the pointer. A look at NTC thermistors does indeed show some very similar looking candidates. There is definitely a burnt smell from this NTC so I'm tempted to replace it anyway. There are also some domed caps near the output.

[stj]

Re: Antec TruePower 380p failed after intermittent supply, suspect MOV

burned glue on the back - that's the smell
check the resistance

[PeteS in CA]

Re: Antec TruePower 380p failed after intermittent supply, suspect MOV

Thermistors sometimes crack or blow apart is there is a really high current short further into the circuit, e.g. a shorted bridge rectifier or switch device. So you have a bad thermistor and some probably bad output capacitor. You also probably have one or more shorted PFC or inverter MOSFET.

[rabbituk]

Re: Antec TruePower 380p failed after intermittent supply, suspect MOV

The 22 ohms that I mentioned earlier was measured across this thermistor. Was it correct to measure it whilst in circuit or do I need to take it out? Is 22 ohms correct for this component?

[PeteS in CA]

Re: Antec TruePower 380p failed after intermittent supply, suspect MOV

The 22 ohms that I mentioned earlier was measured across this thermistor. Was it correct to measure it whilst in circuit or do I need to take it out? Is 22 ohms correct for this component?

Yes, it can be measured in circuit. The actual resistance depends on the specific part, but 22 ohms is credible. However, if it is cracked it is damaged and should be replaced. The cause of the cracking would be as I described above, a very large excessive current. Fuses don't blow without a reason. The same is true of thermistors. The cracking indicates there is a problem elsewhere in the power supply.