HP DM4 help needed.

[cdicky]

Hi all, 1st post.
Sorry to come here to ask but really stuck. Not too hot with laptop repairs.
Although this seems a common problem fo HP.

Basically HP DM4 that had slight corrosion / condensation problem on motherboard. Its all cleaned (about three caps ) and checked for shorts .

Now whether related or not, I assume it must be, board is dead. No lights power or anything. Charging socket has built in led. Also has several wires (some just doubled up) to a board socket, but one is apparently a 'data' return line to charger. Power good circuit?
The charger and battery both been tried in another machine and appear normal.

There is one small chip I cant identify near the power socket thats getting very warm, but other than no power / volts anywhere.
Does anyone have any info, like schematic or experience with these or or similar?
Thanks

[lezsimply]

Re: HP DM4 help needed.

post good quality image. post motherboard code for others to know.

[cdicky]

Re: HP DM4 help needed.

Good idea- thanks
Not sure if this will work by linking.

http://picasaweb.google.com/11584027...eat=directlink

[Th3_uN1Qu3]

Re: HP DM4 help needed.

If you had corrosion, shorted ceramic caps are common. Start from the input jack downwards.

[techman1025]

Re: HP DM4 help needed.

Hi
When you plug in dcjack is the led for jack lit? No ?? if no and power adapter is good and also dcjack and have the 19V coming in then i would start with bios firmware known problem (if you give me full model i would upload a new clean dump... if dcjack is lit then move on to alwson voltage 3/5 ..with adapter plugged in and don't press power button just check all the big square coils until you find the 3/5 they will be side by side and all the rest coil want have voltage until power button is pressed. let me know
Techman1025

[cdicky]

Re: HP DM4 help needed.

Pretty certain NOT bios or any other software problem.
Because it is not getting any power. The charger works in another machine but not this one.
Ive been told and evidensed by the jack socket, that there is a data pin to the charger. Basically the logic circuits disable the charger (or prevent it switching on) there by limiting any power to the board. I've poked around with a meter but volts just flicker around the half volt mark.
I cant see / dont know the circuit that controls this. Maybe its not but maybe a fauly shorted or open transistor. Trouble is there are many different types with different values.

[cdicky]

Re: HP DM4 help needed.

Just a little update / progress report.
Identified 2 transistors that pretty sure have one leg short circuit.

They are 12w 13 or here BSR13R SMD Transistor http://www.ebay.co.uk/itm/BSR13R-SMD...-/160937411559

Bit pricey though.
And unfortunatly there is still a def short. (after removing them)
I also re-cleaned and dried the board making sure no memnants of any crap remained.
one bit of shock as the penny dropped. After removing all the plastic + shrouds realised the cpu + gpu are glued to the board.
So if a new replacement is found cheap enough, its got to include these as well aaagh
https://www.badcaps.net/forum/images...es/lolsign.gif

[techman1025]

Re: HP DM4 help needed.

Hi
The center pin is the data pin so this is how the laptop knows adapter type watts and so on this will ONLY prevent it from charging it will not prevent it from power on ..a warning will appear telling you to type F1 to continue . so it will power up and run it just want charge if it's the wrong adapter meaning watts rating or type even if center pin is broken same out come.
Techman1025

[techman1025]

Re: HP DM4 help needed.

Hi
The center pin is the data pin so this is how the laptop knows adapter type watts and so on this will ONLY prevent it from charging it will not prevent it from power on ..a warning will appear telling you to type F1 to continue . so it will power up and run it just want charge if it's the wrong adapter meaning watts rating or type even if center pin is broken same out come.
Techman1025