Laptop AC adapter voltage drops

[RotVik]

Hello everyone! first I tried search and find nothing, maybe I didnt search well enough? anyways...

I have this AC adapter, it is an HP 19.5V 3.5A central pin plug, when connected it powers on and delivers the voltage correctly and stable, when I Plug it into the laptop and power it ON it immediately drops to 6v-9v up and down, when I unplug it it takes like 3 seconds and go back up to 19.5v stable
So far I desoldered the main Cap as well as te 2 otput ones, tested and measured them, capacitance is ok and the ESR values seems OK, the big 120uf 400v ESR was .15, I replaced it with another one with .26 ESR and same result

I am not sure if those values are good or bad, any suggestions? Thankyou all!

[stj]

Re: Laptop AC adapter voltage drops

where did you read the voltage from?
and did you test the laptop with a different supply incase it is overloading the supply?

[RotVik]

Re: Laptop AC adapter voltage drops

where did you read the voltage from?
and did you test the laptop with a different supply incase it is overloading the supply?

I read the voltage directly from the 3 terminals on the adapter, and the plug, cable seems fine, no short, continuity and resistance ok
The laptop works fine with another adapter no problem

[SMDFlea]

Re: Laptop AC adapter voltage drops

I read the voltage directly from the 3 terminals on the adapter, and the plug, cable seems fine, no short, continuity and resistance ok
The laptop works fine with another adapter no problem

Whats the adapter model number

[RotVik]

Re: Laptop AC adapter voltage drops

Whats the adapter model number

Model:PPP009C
HP Part No. 677774-002

[stj]

Re: Laptop AC adapter voltage drops

well if the output caps are o.k. then i would try replacing the output rectifier incase it's breaking down under load.

[momaka]

Re: Laptop AC adapter voltage drops

So far I desoldered the main Cap as well as te 2 otput ones, tested and measured them, capacitance is ok and the ESR values seems OK, the big 120uf 400v ESR was .15, I replaced it with another one with .26 ESR and same result

Mains cap should be fine, as this adapter does not appear to have an APFC circuit. So I would suggest putting the old mains cap back in, since it's made by Rubycon, which is a very reliable Japanese cap manufacturer.

You say the two output caps also tested OK for ESR and capacitance, but were they within tolerance on the capacitance (+/-20%)? If higher than 20% over printed capacitance on sleeve, they've broken down with high leakage current... which is the most common way I've seen Ltec caps go bad. On that note, even if the Ltec caps are good, I would suggest replacing them once you get the adapter working.

Also, there should be small 5x11 mm electrolytic cap somewhere near that big mains cap, and is typically what is responsible for startup and maintaining operation of the PWM chip on the primary side. So when you do find that cap, take it out and check it out on the ESR meter for proper ESR and capacitance. That could be one of the reasons the adapter is failing under load.

Another thing to try is to solder a bridge across the R015 SMD resistor on the solder side. This resistor is responsible for detecting output over-current condition. If it has drifted out of spec (pretty much impossible to measure with a regular DMM), that could also be what is causing the adapter to shut down under load.

[RotVik]

Re: Laptop AC adapter voltage drops

well if the output caps are o.k. then i would try replacing the output rectifier incase it's breaking down under load.

Ill look into that

Mains cap should be fine, as this adapter does not appear to have an APFC circuit. So I would suggest putting the old mains cap back in, since it's made by Rubycon, which is a very reliable Japanese cap manufacturer.

You say the two output caps also tested OK for ESR and capacitance, but were they within tolerance on the capacitance (+/-20%)? If higher than 20% over printed capacitance on sleeve, they've broken down with high leakage current... which is the most common way I've seen Ltec caps go bad. On that note, even if the Ltec caps are good, I would suggest replacing them once you get the adapter working.

Also, there should be small 5x11 mm electrolytic cap somewhere near that big mains cap, and is typically what is responsible for startup and maintaining operation of the PWM chip on the primary side. So when you do find that cap, take it out and check it out on the ESR meter for proper ESR and capacitance. That could be one of the reasons the adapter is failing under load.

Another thing to try is to solder a bridge across the R015 SMD resistor on the solder side. This resistor is responsible for detecting output over-current condition. If it has drifted out of spec (pretty much impossible to measure with a regular DMM), that could also be what is causing the adapter to shut down under load.

I see, that is helpful information thankyou, Ill look into that and report back as soon as I can!
Do you happen to have one of those adapters at hand? or is there a way to get the diagram or schematics of adapters as well?

[momaka]

Re: Laptop AC adapter voltage drops

Do you happen to have one of those adapters at hand? or is there a way to get the diagram or schematics of adapters as well?

Unfortunately, I don't have that adapter nor any schematics for it. In fact, I rarely look for schematics for these things, as they tend to be scarce, and it usually takes me more time to look through the sea of stuff on the internet than it does for me to take a piece of paper and just draw a crude schematic of the device I'm working on. The only time I look for schematics is when working on amplifiers and CRT equipment, since those contain more specific service info.