Imac 24 PSU Liteon PA-3241-02A

[darjness]

Hello,

My imac died, wont turn on, only 3 leds on, first i tough that motherboard died, but after some search on internet i found that psu tend to fail on those imac aswell. Mofset 060n03lg was shorted, i replaced it, also i replaced all 2200uF 16v caps, but mac still wont power on, fans twitch when i plug the power cord and also when i press the power button. Hdd spins, but if i have many thing running in house like heaters very quickly shuts off, if not it keeps on for long.
Any tips what it cloud be ?

Thx

[darjness]

Re: Imac 24 PSU Liteon PA-3241-02A

New mofset 060n03lg has drain and source shorted, is that normal ?

[budm]

Re: Imac 24 PSU Liteon PA-3241-02A

New mofset 060n03lg has drain and source shorted, is that normal ?

No, you need to remove it off the board and test it off the board again.

[darjness]

Re: Imac 24 PSU Liteon PA-3241-02A

No, you need to remove it off the board and test it off the board again.

I just removed it. pin 2 and 3 are shorted both ways

[budm]

Re: Imac 24 PSU Liteon PA-3241-02A

Shorted power MOSFET should have caused the fuse to blow also, plus the IC that drive the Gate of the MOSFET may be damaged also.

[darjness]

Re: Imac 24 PSU Liteon PA-3241-02A

Shorted power MOSFET should have caused the fuse to blow also, plus the IC that drive the Gate of the MOSFET may be damaged also.

I tested voltage without the mosfet. With mac off i get 12v on drain, 0v on source and gate, with mac on i get 12v on drain, 21.8v on gate and 2.8v on source

[budm]

Re: Imac 24 PSU Liteon PA-3241-02A

Right now I have no idea what the function of that shorted out MOSFET is yet, it is may be part of the SMPS, the PFC, or it may be using as a switch. The connections on the board will have to be traced out to find out.

[darjness]

Re: Imac 24 PSU Liteon PA-3241-02A

Right now I have no idea what the function of that shorted out MOSFET is yet, it is may be part of the SMPS, the PFC, or it may be using as a switch. The connections on the board will have to be traced out to find out.

Source goes to 3 pins that go to the motherboard, Gate comes from somewhere psu and only have voltage when mac is on, drain comes from +12v that also goes to motherboard and its always on. on mofset schematics its says Fast switching MOSFET for SMPS

[budm]

Re: Imac 24 PSU Liteon PA-3241-02A

It sounds like it is being used as a switch to provide Voltage to pin 3 of the connector.
You may want to check pin 3 and Ground to see if there is very low resistance treading that may have caused current over load and took out the MOSFET.

[darjness]

Re: Imac 24 PSU Liteon PA-3241-02A

I tested it, multimeter beeps for half a second than goes to 1 , theres a 470uf 16v capacitor on ground and those 3 pins, pins number are 8 9 10 ,

[darjness]

Re: Imac 24 PSU Liteon PA-3241-02A

Could it be that i bought a bad mosfet ? When i got it i was so excited that i would have my imac up and running that i did not test it before install, since new one is bad also now, i ordered more 5,

[budm]

Re: Imac 24 PSU Liteon PA-3241-02A

So the original one was shorted and now the new one is also shorted out?

[darjness]

Re: Imac 24 PSU Liteon PA-3241-02A

So the original one was shorted and now the new one is also shorted out?

Yes, the original is shorted on all 3 fets, the new one source and drain are shorted and 59 ohm's on drain and gate

[budm]

Re: Imac 24 PSU Liteon PA-3241-02A

That is strange to have Drain to Gate damaged also.

[darjness]

Re: Imac 24 PSU Liteon PA-3241-02A

I think the best thing to do now is to wait till monday, when i receive those new mosfets, and than i will test it before install. I found that the problem is this mosfet after searching the net and bad caps forums, they fail very often and most of times psu runs after replacement, also chinese replacement psu´s looks on pictures like they replace this mosfet only and sell them.

[darjness]

Re: Imac 24 PSU Liteon PA-3241-02A

That is strange to have Drain to Gate damaged also.

I found now the old one and tested it again and it has 20 ohm's on drain and gate

[darjness]

Re: Imac 24 PSU Liteon PA-3241-02A

That is strange to have Drain to Gate damaged also.

Hey,

Mosfet arrived, tested first good values, soldered to pcb,tested mosfet again and all good, power in,voltages are good, power mac on, fans twitch and 3 leds, I power the mac off test mosfet again and its shorted.

Any tips what could be the issue ?

Thx

[domas]

Re: Imac 24 PSU Liteon PA-3241-02A

something on the output partially shorted/leaky?

[darjness]

Re: Imac 24 PSU Liteon PA-3241-02A

something on the output partially shorted/leaky?

I cant find anything shorted and nothing is leaky , Maybe something shorting on motherboard when turned on ?

[domas]

Re: Imac 24 PSU Liteon PA-3241-02A

i wouldn't say so.

It would trip the OC protection IMHO.

You mentioned that it does work fine for few minutes. So turn it on without the mb and check all the rails for out of tolerance voltage. Including low power -12 and the like (not sure what imac voltages are)

if they all are fine, try plugging it to mb starting the computer and check which ones are out of tolerance. But limit the time for that as it will bur again.

I had a psu where i shorted -12 rectifier and was unable to spot it as it was under a big choke. It did not have oc protection and it would burn the primaries upon the start up.