DELL Laptop Charger Repair

[abuhafss]

Hi

My laptop charger stopped working.
I opened the casing and found the big capacitor 120µF 400V (mfg TAICON) to be damaged.

I have a new 100µ 400V (mfg SAMXON) lying in my capacitor box.
Will it do the job or I should buy 120µF?
And replacing the faulty cap with a new one is enough or first I need to check for the cause, why the cap had gone bad?

 

[duke37]

I do not think that 100μF will be much worse than 120μF. They are not made to high cacacitance accuracy. Of more concern is that the picture shows a 420V capacitor, not 400V. You do not say what your mains voltage is.
If you try the new capacitor, start it up through a lamp limiter.

Get a 105deg cap, not 80deg.

 

[abuhafss]

I do not think that 100μF will be much worse than 120μF. They are not made to high cacacitance accuracy. Of more concern is that the picture shows a 420V capacitor, not 400V. You do not say what your mains voltage is.
If you try the new capacitor, start it up through a lamp limiter.

Get a 105deg cap, not 80deg.

It was a typing mistake.
My mains voltage is 220V.

Would you please kind enough to elaborate "start it up through a lamp limiter".

 

[davenn]

It was a typing mistake.
My mains voltage is 220V.

Would you please kind enough to elaborate "start it up through a lamp limiter".

use the correct 120uF and 420V

 

[duke37]

A lamp limiter is a filament bulb placed in series with the mains supply. The maximum current which can be drawn is that of the lamp so things start up gently. If the lamp stays bright with no load on the power supply, then something is wrong but you are unlikely to blow fuses.

I use a lamp limiter to start up old valve radios which contain high voltage electrolytic capacitors. When things look reasonable, the lamp is by-passed and the radio gets full mains voltage.

220V sine wave rectified will give a voltage of 310 so there should be plenty of spare capability. However, the mains may not be sine, the voltage may be much higher than nominal and there will be spikes of unknown voltage and duration.

 

[abuhafss]

I replaced the cap with 120µF 450V 105°C and of course the fuse T3.15A which was blown.

The charger worked perfectly for 3-4 days but last night suddenly the fuse banged again. What could be the reason? Please suggest me some tip to move ahead. Here is the schematic of the charger, I found on net.

 

[davenn]

The charger worked perfectly for 3-4 days but last night suddenly the fuse banged again. What could be the reason? Please suggest me some tip to move ahead.

possibly the bridge rectifier or the MOSFET Q1, intermittently failing
if the fuse is blowing harshly, I would suspect the bridge rectifier, otherwise Q1

 

[pharaon]

Here is the schematic of the charger, I found on net

what did you search for to get the schematic
i have same problem with my adapter and need to find the schematic to repair it

 

[abuhafss]

what did you search for to get the schematic
i have same problem with my adapter and need to find the schematic to repair it

"Dell Laptop Charger PA-12 circuit"
I found all the parts tallying with the schematic.

 

[abuhafss]

if the fuse is blowing harshly, I would suspect the bridge rectifier, otherwise Q1

Here is a snap of the fuse with blow stain. I can't judge if it is harsh or not. But its body is not damaged.

 

[kagen]

If i worked for 3 or so days the check the three prog transisters they are failing to clump the voltage so they are shorted from inside

 

[abuhafss]

If i worked for 3 or so days the check the three prog transisters they are failing to clump the voltage so they are shorted from inside

What do you mean by three "prog transistors"?
There are only two of them --- Q1 mosfet K3569 and Q3 BJT 2N3904.