Dell laptop LA90PE0-01 charger repair

[islam_asker]

Re: Dell laptop LA90PE0-01 charger repair

thank you

[eccerr0r]

Re: Dell laptop LA90PE0-01 charger repair

Yay some one (probably some cheap chinese company) doesn't know how to reliably make a wire!

Come to think of it, I've rarely if ever come across a through hole resistor that came up infinite ohms except if it has been mistreated, but for SMT of the few I've worked with... seems more prevalent. Why...

[clearchris]

Re: Dell laptop LA90PE0-01 charger repair

Thanks so much for this thread. My charger was intermittent and then it wouldn't supply hardly any current to charge the battery and would switch off.
It must have taken a good three hours to get the case off and dig out all the white plastic but the good bit was finding the 0 Ohm resistor open circuit. I didn't have an 0603 in stock so an 0805 went in and all was well. I also changed the 47uF 35v cap as it was showing a high ESR (approx 1.5 Ohms) which got a lot worse with a touch of freezer.

I was wondering how long it took you to dig that all out. I took one apart for fun, saw the glue and said nope! If we were lucky, it might be thermoplastic, maybe warming could soften it, but probably not.

[midibob]

Re: Dell laptop LA90PE0-01 charger repair

Thanks so much for this thread. My charger was intermittent and then it wouldn't supply hardly any current to charge the battery and would switch off.
It must have taken a good three hours to get the case off and dig out all the white plastic but the good bit was finding the 0 Ohm resistor open circuit. I didn't have an 0603 in stock so an 0805 went in and all was well. I also changed the 47uF 35v cap as it was showing a high ESR (approx 1.5 Ohms) which got a lot worse with a touch of freezer.

[sam_sam_sam]

Re: Dell laptop LA90PE0-01 charger repair

Or they are very poor quality devices

[tuletula]

Re: Dell laptop LA90PE0-01 charger repair

Hello, sorry for my bad English, I just faced a repair of this same charger, and the damaged component turned out to be the capacitor that goes to pin 3 of the LTA804, the capacitor was short-circuited, and therefore the charger was turned off on the blue tip LED, and voltage at 0 volts. I hope it helps, and by the way I measured all the things that you attach here and I reviewed some somewhat cloudy welds.

[djidji77]

Re: Dell laptop LA90PE0-01 charger repair

first of all, I want to thank you Dannyx for posting schematic diagram of this very poor builded SPS!! you save me a lot of time!!
I had a simillar problem like you i.e. thera was no any power at the output but at the same time on first look there was not anything burned inside. like you, I spend some couple of hours for removing this nonsense foam from PCB and upon partial cleaning I start to measure some voltages. so there was the stable 325V across the C051 and also there was stable 21.7V on pin1 of LTA804N so the next thing what I did was checking capacity of all electrolitic capacitors on PCB using the Tonghui LCR meter and without removing capacitors from PCB. all of them were fine so I decided to check all 3 MOSFet and they were fine too. then I decided to search on internet to see if sombode else experienced similar problem and I find this thread. I saw that couple of you had eggzactly the same problem like me and that in yours cases the problem were in bad soldering of 0R resistors so had done checking it and they all were soldered OK. upon that failed atempt, I took osciloscope and checked if there is any waveforme at Q050 gate and I find out that LTA804N was giving some signal which was immediately shuted down so at that point I knowed that some bad soldering is a problem. after checking all components in Q050 circuit I discover that end of 511R resistor which goes to pin 10 of LTA804N was bad soldered and its resoldering resolve my problem.
once more, thank you all!!!

[MPFI]

Re: Dell laptop LA90PE0-01 charger repair

Well, I know I 'm not that lucky. Second of charger in the batch same symptom. Found the same 0 ohm resistor opened ... but nothing on this one. Chip has HV, VCC is 20V and drops to 15V. every second or so. Like it is trying to start ?. But I cant see ANYTHING in the gates .... nothing. Here is where I got lost. The PFC section is not supposed to work because of the chip ?. I mean, I got 300V on the main cap. But the PFC mosfet is doing nothing ..., at least no activity on its gate. I will re-read above for tips in case I missed something.

[MPFI]

Re: Dell laptop LA90PE0-01 charger repair

those resistors are used to pass over other tracks, it's possible the person who designed that forgot to take into account how much current was flowing when they chose the resistors.

Could be, but in this case are related to the optocoupler cricuitry (output side) I dont tink that the current could be that high.

[stj]

Re: Dell laptop LA90PE0-01 charger repair

those resistors are used to pass over other tracks, it's possible the person who designed that forgot to take into account how much current was flowing when they chose the resistors.

[MPFI]

Re: Dell laptop LA90PE0-01 charger repair

I just registered to thank you for the solution. It helped with my DELL charger as well. Done some measurement. I concluded that the chip was good since the PFC was OK, I got 300V no problems. but measuring arund the optocouples ... got lost. I found a 0 jumper opened. Wondering if the boar design, that has two major holes to fit the low profile transformers (on coil and one transformer) just weakened the board and could crack SMD components. Could be the reason for the silastic flood (YES ... I spent a lot of time cleianing this LOL).

Many thanks !!!!

[eckibear]

Re: Dell laptop LA90PE0-01 charger repair

Hi all,

I found this blog very helpfull, thank you guys!
I've encountered yet another zero-Ohm "fuse" in my power supply of this type. This 0R resistor does not appear in the schematic. It is placed between the upper winding of Transformer T050 and the anode side of diode "JSW" & R-52k3, on the very top of the schematic. It is marked up by the yellow circle below (the red circle shows the zero Ohm Resistor/"fuse" discussed above).
BTW.: My supply was way more filled up with the white silicon putty, hardly any area was left open. I guess it had been very cheap on that day of manufacture.

Cheers,
eckibear

[Dannyx]

Re: Dell laptop LA90PE0-01 charger repair

Did you reflow the broken solder joint I circled on the back of the board?

Yes I have. I've actually reflown MANY other joints for good measure

[delaware74b]

Re: Dell laptop LA90PE0-01 charger repair

Did you reflow the broken solder joint I circled on the back of the board?

[sam_sam_sam]

Re: Dell laptop LA90PE0-01 charger repair

I would put in one those resettable fuses
I will post a photo of one later

This is the kind of fuse that I was taking about
Polyswitch Resettable Fuse 170mA 120V 2 Pin bel0017RM PTC | eBay

For some reason the link doesn't work

[budm]

Re: Dell laptop LA90PE0-01 charger repair

OK, I see that now.

[Dannyx]

Re: Dell laptop LA90PE0-01 charger repair

https://www.badcaps.net/forum/attach...1&d=1485884098
Can you show us where that '0' Ohms resistor on the is?

Above the top-right corner of the PFC inductor (that's the yellow square at the bottom in the picture you linked), there's a hole - you can see a "0" right above that hole, placed vertically in the picture. Sorry, I didn't feel like downloading the pic again and marking it in MS Paint

[budm]

Re: Dell laptop LA90PE0-01 charger repair

https://www.badcaps.net/forum/attach...1&d=1485884098
Can you show us where that '0' Ohms resistor on the is?

[Dannyx]

Re: Dell laptop LA90PE0-01 charger repair

Yeah... I had another look at the schematic. If that 0 ohm resistor went open or high in value, it will sour your day quickly. As sam_sam_sam stated, they used that 0 ohm resistor as a fuse.

Ok, but (so far at least), nothing's really complaining...it might fail again sooner or later though. What exactly is that "fuse" protecting and what was its cause of failure ? I see it's in series with the AUX winding, but I couldn't find any shorts - none at all...

[CapLeaker]

Re: Dell laptop LA90PE0-01 charger repair

Yeah... I had another look at the schematic. If that 0 ohm resistor went open or high in value, it will sour your day quickly. As sam_sam_sam stated, they used that 0 ohm resistor as a fuse.