Laptop adapter LED flashing

[hercooles]

Hello!

I got a Shin 20V ~4.5A. Problem is on load laptop adapter's LED starts flashing. Without load 20V is measurable.
I tested it with 19V light bulb, laptop is working wine with another charger, so 100% it is a charger problem.

I already opened the laptop adapters case. Any ideas where should I look for the problem?

Thanks

[tom66]

Re: Laptop adapter LED flashing

Check the startup cap - primary side around 10uF to 47uF.

[hercooles]

Re: Laptop adapter LED flashing

Thanks for your reply. Startup caps looks OK, but I just noticed that the 450V/100uF worned out. Can I use 400 or 420V /100-150uF instead of 450V?
Thanks

[budm]

Re: Laptop adapter LED flashing

It depends on if this power supply has PFC Voltage booster or not since typical power supply with PFC will be running B+ at around 400VDC. Also if the Power supply is made for 230~270VAC and without PFC, the voltage on the cap can still get very high, @270V DC on cap will be a shigh as 382V (1.414 x line voltage).

[tom66]

Re: Laptop adapter LED flashing

The startup cap can fail with no bulging or obvious visible signs.

Are you in a country with 115V AC or 230V AC?

[hercooles]

Re: Laptop adapter LED flashing

Local electricity "is" 230 AC. I will check the startup caps too, but this 450V is definetly bad. In 19V 4.74A adapters i found 400V/120-150uF caps. This one is 20V/4.5A.

Thanks for your replies Guys!

[budm]

Re: Laptop adapter LED flashing

The cap voltage is depended on the circuits design, the topology, and the requirement of the end user such as operating Voltage range.

[aaronmarsh632]

Re: Laptop adapter LED flashing

Hi,

I have seen a few laptops with this fault description, I have one at the moment which is doing this exact thing. Where can the 'startup cap' be found usually and does it just look like a standard cylinder shape? can anyone offer any example images of a laptop motherboard displaying this component please?

thanks