NEC M400 Blank Display

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oq99

5 posts

Wannabe Geek

#6268 11-Jan-2006 15:19

I'm new here,
I had a problem with my NEC M400, When I turn on the screen is blank. I have solve this before when this problem first time come, I left turn off for a Day so when this M400 turn on everything back to normal. But when I restart it, the problem come again, and now after trying again like I do before (left it off for a day or more) still not work., display blank.
I try connect to external Display but still not work just blank.
I look something wrong with LED on front panel (Wireleess LAN LED). If this turn off the notebook working well, but now the LED still on event I try to turn on anf off several time.
Does anyone can help me?
Thank's

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6 posts

Wannabe Geek

#27901 6-Feb-2006 17:58

Hi oq99, I just signed up here looking for some talk about the NEC M400. I have a unit here which has exactly the problem you describe. The fellow that owns it has had no problem for a year or two but now it very rarely starts up. I am guessing that the Pentium4 does not get reset properly on power up or that not all of the voltages inside come up correctly. I have not been able to find any service manual as yet. I was going to try flashing the BIOS with the latest version in case it was something strange in the boot timing that NEC may have fixed. I am also keen to see if I can just find a reset jumper on the main board to try once it is frozen with all the LEDs on.
Have you been able to find anything more about the problem? Or spoken with NEC? The one I have is out of warranty I am told but only just when the problem first started.

joe

Compass_be

2 posts

Wannabe Geek

#28399 14-Feb-2006 12:04

Hello,

I've the same problem over here. A friend has given me his Packard Bell IGO2000 alias NEC VERSA E400 laptop for repair.

When I depress the power button, the lights are lit, but the pc doesn't boot. The screen will stay pitch black. The hard disk spins, but does nothing.

In my opninion, the reset signal on the cpu doesn't go positive because of power malfunction.

I've disassembled the whole laptop, searching for faulty contacts, debris ... but I didn't found anything particular. I also measured every "fuse resistor", they are all good to.

However, sometimes I can boot the laptop, especially when I have disconnected the power supply and battery. Left the laptop for some hours without power. When I plug in the external PSU, the laptop comes to life. I powered it off and pressed again on the power button to start it again, now it does function. Half an hour later, it won't function anymore until I disconnect all power.

I've been measuring with an oscilloscope when it doesn't function. 5V rail is OK, DC-DC convertor seems to function because I can see the chopped dc on fuse P0507. So what's wrong then ?? Beat me, without service manual or schematics there isn't any way to solve the issue.

Let me know if you make any progress !

With kind regards,

David Thijs
Belgium (dutch speaking)

oq99

5 posts

Wannabe Geek

#28418 14-Feb-2006 14:51

Hello Green joe,David Thijs,

At least I can't find what is exactly problem with my NEC M400.
Finally I bring it to the NEC service centre, and take a 3days for repaired.
When I ask them about the problem, they just say trouble in the mainboard.
Not specific description, but now my laptop is working well.
It's take a cost around $.20 (USD).

For your information, warranty of my unit has expired, but I'm not broken the seal
so I didn't try to disassembled the whole laptop.

Oki

Compass_be

2 posts

Wannabe Geek

#28469 15-Feb-2006 04:27

Hello,

Thank you for the reply, now I'm pretty sure that it is a problem in the mainboard. Probably a faulty capacitor (sometimes it works, somtimes not)

I will replace some of them !

Thnx alot !

David

greenjoe

6 posts

Wannabe Geek

#28662 16-Feb-2006 23:27

That seems like a good repair deal from NEC for USD20. Down here in Australia they charge AUD110 just to have a minimal look. I have had a closer look at my problem one now and I am pretty certain that it is the main core voltage rail which is controlled by the CPU between 1 and 1.75 volts on the Pentium4 (i think these are the correct figures from memory) This rail is definitely not present when the unit does not boot. The rail is controlled by a dedicated PWM controller chip designed for the Pentium4 ISL6247 from intersil. I dont think the chip itself is the problem I think it is just shutting down due to a momentary over voltage. I dont think there is any provision for resetting this chip and it will stay shutdown until the supply voltage is cycled. I am going to try and toggle the Enable pin on this chip manually as this resets it and see if the rail then comes up. I will also try and see what is causing what i think is a very brief voltage overshoot which is sufficient to shut it down. Yes I agree it may be a capacitor. it gets pretty hot inside and this can ruin the electro ones. My only problem is that I can not find the pinout for the Intersil ISL6247 chip. Intersil say they only make this information available for developers. I have the info on the version of the chip for the AMD processors which is very similar but has only 32 pins unlike this one which has 40. If anyone can help me with the pinout for this i will be grateful.

joe

oq99

5 posts

Wannabe Geek

#30030 6-Mar-2006 20:18

I'm back,

After smiling for a while, now my M400 making the act of again.
Still same the problem before, so I don't care about broken the seal, now I dissambled
the unit to see what going on with this computer. I have trace day to days to see what
they do (NEC Service centre),this seem like no single part was replace.
Until now, I cannot sure what is axactly problem come to my notebook.

If anybody have find this problem, your help would be appreciated.

Oki

oq99

5 posts

Wannabe Geek

#30385 9-Mar-2006 19:26

if no choice you can buy new motherboard here:

http://www.pchub.com/uph/catf/itemlist.aspx?catid=64&mid=2416&page=1

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greenjoe

6 posts

Wannabe Geek

#31981 1-Apr-2006 22:12

Well the good news here is that I did get my NEC unit to boot reliably. The problem was definitely the core voltage. The ISL6247 pwm controller was shutting down because of some momentary over volatge condition. If i simply shorted pin 34, the enable pin, momentarily to ground then the notebook booted like normal. I used the circuit from Mitac web site for the 8599 model to help . It is not exactly the same but very similar. This enable pin is driven from the voltage regulator chip which generates the 1.2 volt reference. This reference is generated from the 5v rail using a little 5 pin SMD package regulator (MIC5258) which outputs the power good signal which enables the pwm controller. This regulator was working fine but the problem I believe was in the design. The MIC5258 does have an input pin to disable the power good output or delay it but this input is tied high and so there is very little delay between the 5v rail coming up and the 1.2v power good signal going active. The Mitac circuit actually shows a delay by having a capacitor and resistor on the enable input. I initially tried to add in this delay but I damaged the little MIC5258 SOT 23-5 package so things got a lot worse. No chance of buying one of these parts down in Australia so i looked for an alternative. I ended up gluing on a LE12CZ which is a 3 pin regulator in a TO-92 pack. Big but it fits flat on the board. Plus a capactior for its output. As this did not have a power good output the power good signal pulls up to 5v. When I tried this without adding any delay to the powergood it booted. I was tempted to play around some more and add a capacitor on the powergood to delay it but I feared that I would break something else so I just left it like it is and so far it has booted every time. I guess there is sufficient delay in the 1.2v output coming up after the 5v input so all is well.
If anyone wants any better details or circuit diagrams let me know here.
cheers
kim

letstalkpcs

3 posts

Wannabe Geek

#31983 1-Apr-2006 22:39

Hi kim would appreciate any more info you have .I too have the same problem with my laptop

letstalkpcs

3 posts

Wannabe Geek

#32010 2-Apr-2006 14:17

Does anyone know anything about the diagnostic leds on the bottom of these boards. I have
noticed with mine the all come on when power is applied then 2 in the middle go off.
Had it to a laptop tech yesterday ,he has confirmed that it is a supply problem to the cpu .But he wasn't able to fix it.

greenjoe

6 posts

Wannabe Geek

#32145 3-Apr-2006 23:01

First you need to confirm that you are lacking the CPU Core voltage which should be around 1.75V on these Pentium4's and that the other voltge rails like the 5V and 2.5V are present. IF it is just the core voltage missing your problem may be similar to mine so try this. You need to locate the ISL6247 PWM controller chip in the little 40 pin quad flat pack close to the power jackand on the bottom side of the PCB in my model. The enable pin is pin 34 and you need to momentarily short this to ground after you have powered up. The good news is that this part of the circuit is accessible from the bottom of the notebook (at least it is on the NEC model) by removing the CPU/Fan cover. The bad news is that the PWM chip is very small and the pins are very fine. You dont want to short out the wrong one or adjacent pins together so the trick is to find where this pins connects to. On my board and it should be similar on most it will go to the drain pin on a little FET nearby (look for the little 3 pin chips and meter it out with the power off and the battery out. It is then a whole lot easier to short this pin to ground, or you can even solder a fine wire there to make things easier. There are plenty of grounds nearby just meter them out. I actually just used the big earth land around a screw mount hole in the PCB nearby. Now I did make some photos when I had it apart and anotated one with these connections and chips shown but I dont think this forum will allow attachments or inline pics only links to them. If you are still keen or confused let me know and I will stick the pics up on some web space somewhere.

kim aka joe

dig72

10 posts

Wannabe Geek

#32289 5-Apr-2006 13:13

oq99: I'm new here,

I had a problem with my NEC M400, When I turn on the screen is blank. I have solve this before when this problem first time come, I left turn off for a Day so when this M400 turn on everything back to normal. But when I restart it, the problem come again, and now after trying again like I do before (left it off for a day or more) still not work., display blank.

I try connect to external Display but still not work just blank.

I look something wrong with LED on front panel (Wireleess LAN LED). If this turn off the notebook working well, but now the LED still on event I try to turn on anf off several time.

Does anyone can help me?

Thank's

I had the same problem last month. I would turn on my laptop and nothing would be displayed on the screen. Hard drive starts up and everything seems to be fine other than a blank screen.

I took my laptop to NEC service centre and was told that the LCD Inverter was stuffed.

Was replaced now everything is fine.

greenjoe

6 posts

Wannabe Geek

#32376 5-Apr-2006 21:59

Dig72, your problem was a different one. When the backlight inverter goes in your LCD screen you dont get any backlight so it appears that nothing is happening but if you were to connect an external monitor to the VGA port and enable it from the keyboard you would see it boot up ok. You can also shine a torch on the LCD screen and just manage to see what is there and if you can find the mouse cursor you can actually see enough to click on things. The backlight inverter is one of the more common things to fail in a notebook. Can I ask you how much they charged you for the fix? You would also have seen some hdd light activity when it booted. As oq99 correctly pointed out, when the processor never manages to run its reset code the wireless light remains on (even without the wireless option installed)
kim

letstalkpcs

3 posts

Wannabe Geek

#32377 5-Apr-2006 22:08

Kim , tried tried earthing the pin on bootup but i wasn't lucky.All that would happen was it would sem to reboot the laptop .All the diagnostic leds would light up then the couple in the middle would go out.There is definatly some power Getting to the cpu and chipset as both get warm.Looks like i'm looking for a new or secondhand board from somewhere .
Paul

dig72

10 posts

Wannabe Geek

#32433 6-Apr-2006 14:30

greenjoe: Dig72, your problem was a different one. When the backlight inverter goes in your LCD screen you dont get any backlight so it appears that nothing is happening but if you were to connect an external monitor to the VGA port and enable it from the keyboard you would see it boot up ok. You can also shine a torch on the LCD screen and just manage to see what is there and if you can find the mouse cursor you can actually see enough to click on things. The backlight inverter is one of the more common things to fail in a notebook. Can I ask you how much they charged you for the fix? You would also have seen some hdd light activity when it booted. As oq99 correctly pointed out, when the processor never manages to run its reset code the wireless light remains on (even without the wireless option installed)
kim

He charged me $280.00 including parts, 1.5 hours labour and GST.

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