Laptop will not power up

Have been given a Toshiba Protege R400 Mod No:PPR40A-01000L to look at for a friend who is very ill and the machine just will not switch on.

Have tested the adaptor and battery voltage and there is plenty.

Now I don't have much experience with laptops as such and so cannot rule the PSU as the culprit.

When plugged in the blue power light is on and the small yellow battery indicator flickers at random speeds - but quite fast.

I have Googled it but cannot come up with a definitive answer.

Now I have the maintenance manual for it and I can probably get the LCD mask off to look at the power witch itself. But before I do I would like some opinions on the most likely cause and would prefer to avoid this if at all possible.

So any Toshiba / laptop folks out there any suggestions please.

The power button is a likely cause and fairly common. The switch is a simple contact switch: it makes momentary contact between 2 wires to signal the motherboard. If you can find and get access to the 2 wires you can physically touch them together, or use a flat blade screwdriver to momentarily connect the 2 contacts, and that will test whether the power logic circuit is good and the switch is bad. If you make contact and it does not start then you can assume the switch is OK and there is something wrong on the MB side of things.

Before you start disassembly it is always a good idea to do a simple test (perhaps you've done this already):

• First, reset the BIOS defaults: Remove power adapter and battery, press and hold the power button for 20 or 30 seconds, then connect everything again and try to start.
• Then try with just the battery - no power supply.
• Then try with power supply - no battery installed.

If none of the above works then you next want to remove the hard drive, CD-DVD drive, and RAM and try to start (it won't) but you may get some indication it is alive (beeps, info on screen).



Then add one stick of memory and test, then the hard drive, then the CD-DVD drive.


See what you find.

I'll second the power button thought, same thing happened to my hp laptop. It would still work but you'd have to sit there holding down the power button for nearly a minute before it'd start to kick on. Anyhow a littler tinkering fixed it up.

Thanks fellas I have had the switch out and it seems to be working - I'll check again in though as it is easier to get to than I thought, but is soldered onto a very thin circuit board strip with the tiniest circuit lines I have seen I' ll send a pic when I whip it out again. I also disconnected it from the plug to se if the conatcts (non gold) had got dirty but again no difference.
The drive and RAM I did before I took the switch board out and even tried a weird idea from a Google and that was to disconnect the power and battery the the machine upside download with the power switch on for thirty seconds then connect up again but it didn't work.

What has me puzzled is the blue power connect light is on and the yellow flashing battery power light which the maintenance manual tells me that the battery is running low.
All the same I do suspect the switch may be the culprit.

Ok now I have tested the switch it shows full resistance and it goes momentarily 0.1 ohms when pushed.
Back in the machine the connection on the right of the shot shows 3.23v and when the switch is operated the left connection goes momentarily to 3.23v then back to 0v as do the other small holes in that larger piece of copper inlay to the left as one looks at the board. So I think the switch is ok. Teh samll white connector shows 3.23v on all connections bar one.
So am going to open up the back and take a tentative look inside at the mobo.
Am just wondering but suspect the 3.23v supply is just the switching circuit operating voltage. Now does anyone know what I should be looking for in particular places and besides obvious signs of overheating and loose wires / joints please?
I am assuming that the power in – 15v is directed by the power switching circuit via some sort of relay circuit. I only ask as I don't have a wiring diagram to work from.

Personally, once I have isolated the problem to the motherboard then I am done. I'm not going to attempt re-soldering parts. Beyond my skill set.

But if you are determined you should see if you can get your hands on a wiring schematic for that exact motherboard. Similar models may be similar enough, but they do make circuit path changes so the exact model may be important.

But the circuit logic is straight forward:
If Battery only then switch to Battery circuit.
If Power Supply available then switch to PS circuit.
But there is also a Battery charging circuit.

You would have to test the switching continuity on all 3 printed circuits. You've got to have the schematics and specs to do that I would think. You'd just be stabbing in the dark without one.

No change when you ran it without a battery installed?

If you understand how to read a schematic you could figure out which circuit the button completes and try powering it with a manual bypass just to be sure it's the button.

I don't know he's got a point there. It gets pretty complicated once you are dealing with anything directly attached.

Yeah it's not that hard given the right equipment but I ma limited to digi meters and besides until I can get this backplate off then I am not going anywhere.

I was just explaining to G that after removing all the screws it still will not budge and perhaps the processor has melted the plastic back plate enough to make it permanently stuck to the mobo? I just quite lift it enough to see even with a strong pencil beam light.

Was just thinking if it is something replaceable then it might work again, and no it will not power up with or witout power / battery in any comination.

I did think of dropping the drive into the Compaq but the drives are entirely different so maybe I'll try it in my L550 Satellite perhaps even if it is only t get her stuff onto a DVD or stick.

Another suggestion you probably already know:

Check for those sneaky screws under the labels!

TVeblen said:

Another suggestion you probably already know:

Check for those sneaky screws under the labels!

Yeah TV I have had a real prospect of those by feeling for the depressions. Now I have some special solvents here that will get them off but I really don't think I will find much there.

Now in addition that I cannot find any - the maintenance manual says there are 18 screws in all and thats exactly what I got out. It also mentions a latch but apart from the battery holding one I cannot find anything.
In the pic the "offending area" is right below that small rubber button "foot" in the centre and I have checked beneath it and there is just hard plastic which makes me think there is a screw into it from the other side (topside).

Have now removed the keyboard and I think perhaps those three screws (one Torx) are the culprits - thin is the manual is not very explicit for non techs like me probably old hat for some. But am now going to leave it till tomorrow as it's late and thats when I start making mistakes.