Liteon pa-3271-06mx help!!!!

[NConstantinou]

Dear all,


i have the above power supply from Microsoft desktop surface.
fuse was blown and changed.
On input lines L & N i get a very little ac reading.
i checked fuse, filter capacitors, coils, main mosfet and main capacitor and nothing is shown as short except the RV001 which i assume is a NTC varistor.
i removed varistor and applied heat and is decreasing which means works ok.
i remove bridge rectifier and i measured in diode mode and it looks fine.

Is the problem on rectifier, it is not suppling ac!

Thanks

[CapLeaker]

Re: Liteon pa-3271-06mx help!!!!

If you don’t have any AC coming to the bridge rectifier, the problem lies before it. You should have like 230V AC on the input of the rectifier and about 325VDC on the main filter capacitor. Probably something is open like filter inductor or something. Wouldn’t be the first time. Post a clear, high resolution picture from both sides.
Do some continuity checks from the plug to the AC input of the bridge rectifier (line and neutral) and see which side is affected and where you loose it.

[CapLeaker]

Re: Liteon pa-3271-06mx help!!!!

The AC part of the power supply is simple. I marked up a generic schematic for you. If you do find an open filter inductor, unwind one turn and resolder it to the leg. You need to get full AC power mains to the bridge rectifier. Other than that there is no DC from the bridge rectifier into the main filter capacitor.

[momaka]

Re: Liteon pa-3271-06mx help!!!!

If you get no AC, check or re-solder the input connector. Not uncommon to get cracked joints on those and then get nothing to the PCB. If that's not it, check the solder joints of any common-mode chokes on the input. If these two check out, measure voltage on the primary 400V electrolytic cap. Should get close to 340V DC with 230-240V AC input going to the adapter.

[NConstantinou]

Re: Liteon pa-3271-06mx help!!!!

Dear CapLeaker,

Thanks for your reply.
the L & N lines on board show very little resistance. After the first inductor there is a green part label RV which is NTC SCK018 and is a varistor. that measures a small resistance.
Now since at the input wires i do not have 220v AC and all solder points seem to be ok
how i will find the defective part!
i removed from board filter capacitor, first inductor and are not shown as open or short

NOTE:
If i remove RV green varistor then on LN i get 8 MOHMS resistance and increases

[harp]

Re: Liteon pa-3271-06mx help!!!!

On input lines L & N i get a very little ac reading. <===> ... it is not suppling ac!
Is the problem on rectifier, <===> i remove bridge rectifier and i measured in diode mode and it looks fine.

I dont understand what you mean...

Maybe cable or wall socket is defective, try another to replace. From mains to bridge rectifier must be continuity on both wires, that is marked blue and green on Capleaker photo. There is no need to test this under voltage, just use continuity mode to confirm connections between checkpoint.
And one tip: when you do a measurement to inform us, put readings what you actualy have, rather one that you do not have.

[stj]

Re: Liteon pa-3271-06mx help!!!!

no pictures yet?
" first inductor and are not shown as open or short"
????
inductors are supposed to look like a short - they are usually a coil

[harp]

Re: Liteon pa-3271-06mx help!!!!

Something like this

[stj]

Re: Liteon pa-3271-06mx help!!!!

shit pcb layout - plenty of coils to break too.
it probably even has active pfc to break shit

[CapLeaker]

Re: Liteon pa-3271-06mx help!!!!

Dear CapLeaker,

Thanks for your reply.
the L & N lines on board show very little resistance. After the first inductor there is a green part label RV which is NTC SCK018 and is a varistor. that measures a small resistance.
Now since at the input wires i do not have 220v AC and all solder points seem to be ok
how i will find the defective part!
i removed from board filter capacitor, first inductor and are not shown as open or short

NOTE:
If i remove RV green varistor then on LN i get 8 MOHMS resistance and increases

Maybe show us where you measured with the probes on a picture. Just upload the pictures individually in jpg using the same attachment function. Problem is my lil IPAD isn’t having any .rar.
Probably you are having an open, before it goes to the bridge rectifier. Maybe start with the power cable itself. Once that is ruled out, put your DMM in beep mode, hold one end at one pin of the power socket, then go with the other end to the bridge rectifiers two AC inputs. Make sure that L and N make it to there (small resistance). You find for example, the line has continuity from the socked to the bridge rectifier and neutral does not, you just have to trace it back.

[NConstantinou]

Re: Liteon pa-3271-06mx help!!!!

Thanks to harp and the other people for the help BUT specially harp because he had a picture of a power supply and i noticed that i replaced 2 parts in a wrong place RV001 and HS3 green part varistor and black part near main capacitor.
i switched them according to harp schematic and now i do have 320vdc on main
capacitor.
i there any way to test power supply without desktop!
if i short green and black cable it should start! Green cable is label 11vsb!


Thanks everyone

[NConstantinou]

Re: Liteon pa-3271-06mx help!!!!

Dear harp,

the fuse was blown while i was testing power supply BUT the MOSFET on heatsink was burned. and i can not see the number.
is it possible to tell me the number!

Thanks

[harp]

Re: Liteon pa-3271-06mx help!!!!

No I cant check... the picture was found on internet. BUT you can locate a driver IC and according to declarated PSU power choose a some similar mosfet who meet IC datasheet specifications.
Maybe to search for similar schematics or components like


Always use a some kind of bulb current limiter when testing and make note of place and orientation of any desoldered component.