Is there a way to use the Emate 300 without battery pack, I plug it in the wall, the light shitch on but there is no other activity

Yes, the eMate should run without a battery pack.

A few things to check:

1. Are you using an original Newton AC adapter? The correct voltage and current rating is important.
2. It's possible that the display cable has been damaged by a broken spring in the display hinge.
3. Does the display make any odd sounds when moved?
4. Does the display flicker at all?
5. Does the backlight work?

I'm getting back to this project.

I plug it in the wall, the light shitch on but there is no other activity

This emate is pristine.
I'm using the original AC adapter
Hinge and cable are in perfect conditions
Display doesn't make any sound when moving it.
The backlight doesn't light up
It has the two cards in the slots

I disassemble it and check voltage around the board.
The board gets electricity including various components
BUT, the pins on the board that gives voltage to the LCD has no voltage al all.

I checked visually it looks pristine. I reviewed the board as thorough as I could and couldn't find any anomalies.
I don't know what else to do...

Did you install the little plunger back correctly? That pushes a switch to turn the screen on when it's opened. If it's not there, you'd get a symptom like you described. Check the eMate Service Source manual to see the bit I'm talking about.

Thanks for the answer, do you mean the Backlight wire connector?

I'm looking at this document, and can't find what you mention.

Sorry thought it was in service source but it's not. Here's the part.

I think I have a new version of this.
I have like this square thing and this switch on the board...

You're missing the plunger that pushes in the switch

Ohhh.. do you have a better photo of that piece, maybe I could replicate it.

No but you should be able to work backwards by measuring the hole the 'pin' goes through and the enclosure parts where it rests. Good luck!

I got a better image...

Ok, no luck at all.
I replicated the piece. I even fixed the switch on the ON position.
Still only the light turns up. No sound, no sign of light out of the screen.

Could be the screen contrast - slider position or the slider component itself - though if the volume's up then the eMate should emit the start-up sound

You mentioned "It has two cards in the slots" - one should be the ROM card with NewtonOS on it, it should be obvious because the card has spots for four chips, but only two are installed like this https://www.pda-soft.de/common/img/hardware/eMate/disassembly/746x519_emateDisassembly08large.jpg

Problem could be with the expansion card, you could try removing it (with power off of course) but if it boots,
your Newton might decide to wipe its internal flash. Don't do this if you are trying to recover precious data!