Dell laptop LA90PE0-01 charger repair

[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.

[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!!!

[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.

[sam_sam_sam]

Re: Dell laptop LA90PE0-01 charger repair

Or they are very poor quality devices

[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.

[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.

[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...

[islam_asker]

Re: Dell laptop LA90PE0-01 charger repair

thank you