How to fix keys on laptop keypad not working even keypad already replaced.

If you replaced the keyboard and the same exact keys are still not working then you most likely have a system board issue.
But check basic things and make sure before turning to any chip level operation that did you insert the cable properly and is your zip connector or header of keypad is good or broken from anywhere?
Some of my known people who connected with the laptop computer hardware repairing filed but they don't done any chip level work on laptop so they use to send me the faulty laptop for repair in which they feel a chip level issue they do only diagnose and fix only software and common hardware level problem like installation of software, OS and part replacing work replace hard drive, ODD, LCD, Keypad, Touch-pad, Hinge and main board but replacing main board is too much costly.

Some time problem can't get fix after just replacing the part that they think is a faulty spare because they do repair on the basic diagnostic way if keypad not working ( problem can be some keys not working or functioning properly, keypad died not detected at all ) after checked some basic thing like OS issue driver and finally replaces the keypad as usual we all have to do.

But if problem couldn't get fix then its means problem is not a normal issue that will need a chip level operation so as usual they forward me this case. When they come to me most likely they said ''I have replaced the keyboard on this laptop 2, 3, 5 times but sill keypad not working.” These same letters stop working after a while. Replacing the keyboard worked before'' also most of the time same thing happened with mouse touch-pad.

Before I going to tell how can easily repairer this kind of case..I just want to remained you a basic block diagram of laptop motherboard.

As this diagram keypad and touch pad PS/2 controls are controlled by EC chip and if EC chip not present than I/O chip controls the PS/2 control.

Every laptop notebook manufacture uses a different type keypad model and their header for their different laptops models. And there header size and their pin datasheet may not be same. so before wasting your time to get datasheet and any other solution to fix the problem to searching on Google just re-soled the I/O chip and pull up resistor pack capacitor pack or simple SMD resistor which have connected with keypad connector and direct with I/O chip because today laptop manufactures use the I/O chip which have in built EC controller.
You can use hot air blower or a micro iron for re-soldering process… mostly pull up resistor and capacitors has solder nearby the keypad connector or header.

Pay little care if you have not familiar with SMD components.

If after re-soldering can fix you problem then you must have to change the EC or I/O chip :(

have a good luck :)

Power up a laptop motherboard without power button or power strip.

Yes we can power up a laptop without connecting it's power button board or power strip..!! same as a desktop mother board.
It's safe as well as desktop motherboard just you need to know how power system of motherboard is functioning or how it's work as we press power button.

Switching the power 'on & off' is done by circuits on the motherboard.The circuits are triggered to change state by a momentary shot circuit of two points in the circuit. That is done by the push power button. A short-term connection of that button is enough to turn on motherboard. Usually one pin of on/off switch is shant with (ground) GUN. and second pin of on off switch connected with the circuit and always there is stay a (very low power +voltage) high pulse on the track of the power switch as we press the on off switch switch shot the high plus with Ground. and due to ground, plus trun down to low '0' and circuit turn on the motherboard.
Power on and off system controlled by super I/O chip on motherboard of laptop or some time some motherboard manufacture use some component (IC,Mosfet, Transistor) interface between power button and in I/O (input output controller) chip and mostly power switch being connected direct with I/O.

Is it a safe and easy method to on and off motherboard without connecting POWER button PCB or strip while repairing? :-

It is a good and easy way. If you repairing a major fault of laptop motherboard and while repairing there is need to power up motherboard many time and i think you already know what can be happen if we connect and disconnect a ribbon flex cable many times from connectors, connecting tips of the ribbon flex cable may be get tempted and brake! and it is very hard job to recondition a tempted or broken ribbon cable, even it's also a hard and time consuming job if you looking for a same new one cable in your local market.

So that is a very most common problem with flex cables.

How to find a ON and Off button logic track (PS ON signal) on laptop motherboard :-

It,s very easy to find out form where we can turn on a laptop without connecting it,s on/off switch PCB.

set the multimeter on continuity or buzzer range And simply trace the power switch non ground track from switch to it's ribbon flex cable or connector.

follow this video....

CHECK IN THIS VIDEO DEMO HOW TO POWER UP A ACER ASPIRE 5920 LAPTOP WITHOUT USING THE POWER button board or POWER STRIP :-

And in some of laptop main board you will found a already not connected tips for power on off function, So I putt here a image of this kind of laptop motherboard it's image:-

ON board power on,off tip of:- Compaq Presario V6000,Compaq F700,HP Pavilion DV6000 series,HP Pavilion DV9000 Motherboard,hp pavilion dv7.

But mostly we have to find the PS ON track on main board with the help of continuity meter. :P

HAVE A GOOD LUCK :)