Enermax Naxn ENP500AWT

[sebr]

Hello guys,

the PSU of my parents computer suddenly stopped working. Fuse is OK, no 5VSB and so also no other voltages appear if i force it to start. It's totally dead.
I know since its populated with Samxon and Teapo crap, a full recap would first choice but I just wanna get it fixed as the whole computer will be replaced soon.
So what would you recommend as a good guess for starting troubleshooting here? Maybe someone around here also has such a board and got some hint.

[cheapie]

Re: Enermax Naxn ENP500AWT

Nothing obviously bad/blown? Check if high voltage DC is reaching the primary filter cap. Check or change the startup cap(s) (little tiny 30v+ caps).

[ben7]

Re: Enermax Naxn ENP500AWT

Yeah check to see if the main cap is getting power. Check the pfc coil, and the pfc diode. Check the bridge rectifier.

Are you getting 5vsb when not forcing the psu on?

[sebr]

Re: Enermax Naxn ENP500AWT

Unfortunately nothing blown or obvious. On the primary side i found 3 smaller caps and checked their capacity which is in spec. I guess ESR doesnt play an important role here.
The main cap does not get any power. Like I said fuse tested OK and so do rectifier, pfc diode and coil. Also there are a few 0ohm resistors used as jumper/fuse which are good too.

[ben7]

Re: Enermax Naxn ENP500AWT

Unfortunately nothing blown or obvious. On the primary side i found 3 smaller caps and checked their capacity which is in spec. I guess ESR doesnt play an important role here.
The main cap does not get any power. Like I said fuse tested OK and so do rectifier, pfc diode and coil. Also there are a few 0ohm resistors used as jumper/fuse which are good too.

One last thing to check: the NTC inrush limiter. It is usually green or black, shaped like a big ceramic disc capacitor. You will find it on the primary side somewhere around the bridge rectifier.

[370forlife]

Re: Enermax Naxn ENP500AWT

Just a thought, but are you using the same plug to bench test it as well as when it was in the computer? If so, check and see that the cord is getting power when plugged in, if so, you can also check the soldering on the socket in the PSU itself.

[sebr]

Re: Enermax Naxn ENP500AWT

Across the NTC (or varistor?!) i can measure around 500k in circuit. The power cord is not faulty either.
No 5VSB present, not matter if i try to start it or not. I just checked with my scope , it's totally dead.

[ben7]

Re: Enermax Naxn ENP500AWT

Across the NTC (or varistor?!) i can measure around 500k in circuit. The power cord is not faulty either.
No 5VSB present, not matter if i try to start it or not. I just checked with my scope , it's totally dead.

Across the NTC. more than 10 ohms means it is bad (open circuit)

[Behemot]

Re: Enermax Naxn ENP500AWT

I'll re-open this thread. First I've noticed, there is some serious sparking going on in the main switch when I turn it on but that is not really the problem. Problem is it squeezes (frequency changes when I turn it on), I have been told it was having problems starting up and finaly gave up.

However, no bad caps anywhere, at least from what I've measured. Couldnť reach a few small ones but it's unlikely they are bad. Everything on +5 V SB is OK, either PWMs cap or output caps. I got voltage all right at +5 V SB, just PWR On is somewhat low at 2 volts or so. But it turns on with no load. Any suggestion? Time to bring up O-scope?

[kc8adu]

Re: Enermax Naxn ENP500AWT

the sparking may be the problem.bad contacts causing the sparking and too much drop for it to run under load?
this unit does not appear to have an ntc so the o.p can skip that step.
something is open though if nothing at main filter cap.
iirc i saw one of these with a lead eaten off the pfc coil by brown glue.this unit in the pic seems to be using rtv.

[Behemot]

Re: Enermax Naxn ENP500AWT

The spark only apears once when I switch it to "1" position thus powering it on, it's nothing continuous. Strange thing is that there IS NTC, just in front of the input capacitor, that's why I even mentioned it.

I am not able to determine where the whistling comes from, it sounds almost same from primary through stand-by rail to secondary.

[kc8adu]

Re: Enermax Naxn ENP500AWT

only thing i see is a mov.
must be on the input board if there is one.
the spark tells me there probably isnt one.unless you only get a spark on the second turn on after the ntc is hot.

[Behemot]

Re: Enermax Naxn ENP500AWT

You can barely see it under the yellow glue right next to input cap. It's quite common these days to place it right after PFC output, in front of bulk capacitor to make it initially charge more slowly.

[Escort Eagle]

Re: Enermax Naxn ENP500AWT

What is your problem ? Is it whistling or not running totally or running normally but not running with load - what ??

[Behemot]

Re: Enermax Naxn ENP500AWT

Problem is it squeezes (frequency changes when I turn it on), I have been told it was having problems starting up and finaly gave up.

I assume it was having problems starting up with load as it turns on with no load.

[Escort Eagle]

Re: Enermax Naxn ENP500AWT

When it is turning on without Load, then is it producing isisisisisisisishhh.... sound and at that time is PG coming out ??

[Th3_uN1Qu3]

Re: Enermax Naxn ENP500AWT

When it is turning on without Load, then is it producing isisisisisisisishhh.... sound

That is normal. It's not designed to work without load.

[Behemot]

Re: Enermax Naxn ENP500AWT

Power good is present.

[Escort Eagle]

Re: Enermax Naxn ENP500AWT

At first you should check your Output Diode brackets . Sometimes One side of one Diode bracket goes open . This is why it can not deliver adequate current to the load and keeps PSU off . Check output diodes by removing from the PCB .

[Behemot]

Re: Enermax Naxn ENP500AWT

I can see this at O-scope now can I? The output wave would be distorted if some rail worked as single-way rectifier. Removing these things is not really that easy and it may very well be waste of time…