very challenging issue! lenovo G50-80?

[Weelcup]

I have a Lenovo G50-80 motherboard. aclu3/aclu4 UMA NM-A362 REV1.0.
the board is not turning on. no +3VALW, or +5VALW.
the charging IC is BQ24737. there is 20v in pj302 jumper, however. and it goes inside pu904. but PU904 is not providing the +3VALW.
what confuses me is the short between +3VL and the ground at 51 ohm. i tried very hard to find the cause with no luck.

i have two main question:
1- the pu904 ic should receive the EN signal from the IO. but it does not receive any. can i know what is the main power for the IO ic. because it seems that the ic is not receiving any power signals?

2-i have removed the IO ic from the board now. but still the is a short between the +3VL and the ground at 51 ohm. any suggestion is appreciated so much.


please help?

and thanks in advance

[mcplslg123]

Re: very challenging issue! lenovo G50-80?

You are not getting EN1 signal on PU904 coz of missing ECON signal from IO(Most Likely). First you check whether io is getting power. Check PIN11(VCC) and PIN74(avcc) of IO. Both should read 3v. If you are not getting any voltage here then io will not work at all. Also check whether PIN11 and pin 74 is shorted to gnd or not.

[Weelcup]

Re: very challenging issue! lenovo G50-80?

You are not getting EN1 signal on PU904 coz of missing ECON signal from IO(Most Likely). First you check whether io is getting power. Check PIN11(VCC) and PIN74(avcc) of IO. Both should read 3v. If you are not getting any voltage here then io will not work at all. Also check whether PIN11 and pin 74 is shorted to gnd or not.

Thanks for reply

That is exactly what I needed to know.. there is no short to ground . And there is no pOwer getting to these pins. I mean there is no 3v present on both pins.
Now can I ask which ic should provide the 3v for these pins ?

[JaroTech]

Re: very challenging issue! lenovo G50-80?

Hi, PU904 provides the +3VL, what voltage do you have on pin 5 of the PU904?

[Weelcup]

Re: very challenging issue! lenovo G50-80?

There is 20v entering the ic through pin 7. But there is 0v on pin 5

[JaroTech]

Re: very challenging issue! lenovo G50-80?

Can you remove the jumper PJ304 and measure pin 5 again?

[Weelcup]

Re: very challenging issue! lenovo G50-80?

I already removed the jumper to avoid the short but still 0v on pin 5!

I also removed the IO chip.

can the pu904 chip provide any output in the absence of both EN1 and PG signals?

[JaroTech]

Re: very challenging issue! lenovo G50-80?

I don't have the datasheet for the PU904 (SY8206BQNC), on page 47, PU904 provides the + 3VLP to the EC and the EC allows the EC_ON for the PU904 to provide the + 3VALW. To check what I said is true, you should have + 5VLP on pin 7 of the PU905.

[Weelcup]

Re: very challenging issue! lenovo G50-80?

Thanks for reply
You are absolutely right. There is 5v at pin 7 pu905.
I reattached the picture and show the voltages I have on that area.
This all without IO chip. I also attach SY8206CQNC datasheet and SY8208BQNC.....

[JaroTech]

Re: very challenging issue! lenovo G50-80?

The capacitor with the 3.3V is connected to what?

[Weelcup]

Re: very challenging issue! lenovo G50-80?

The capacitor with the 3.3V is connected to what?

it is connected to PU905 pin 5

as in pic

[JaroTech]

Re: very challenging issue! lenovo G50-80?

If you have 0V on pin 5 of PU904, the PU904 is defective or the PC1055 capacitor is short to ground.

[Weelcup]

Re: very challenging issue! lenovo G50-80?

there is no short to ground in the capacitor but when I put the jumper back the short will come to the capacitor. I mean the jumper PJ304.
but I replaced pu904 and it was just like your suggest (Thanks a lot ). the 3.3v appeared on the capacitor PC1055. I wasn't suspecting the pu904 as I had already replaced it with new one. but it seems that the short in jumper PJ304 defected the new one as well. however, now I replaced it again and have the 3.3v back to PC1055. now what could cause the +3VL side to short to ground with 51ohm. I don't want to test which component is heat by putting the jumper back because I believe that it will defect pu904 again.

[JaroTech]

Re: very challenging issue! lenovo G50-80?

If you have a bench supply, you can inject 3.3V across the PJ304 and look for any component that gets hot.

[Weelcup]

Re: very challenging issue! lenovo G50-80?

I don't have a power supply. But can I use the motherboard bios battery for that purpose. Or it needs a higher amper.

[JaroTech]

Re: very challenging issue! lenovo G50-80?

This will have no effect.

[JaroTech]

Re: very challenging issue! lenovo G50-80?

The +3VL is connected to 12 components via PJ304 from +3VLP. You will need to remove them one by one to determine where you have the 51 ohms.

[Weelcup]

Re: very challenging issue! lenovo G50-80?

The +3VL is connected to 12 components via PJ304 from +3VLP. You will need to remove them one by one to determine where you have the 51 ohms.

thanks a lot ... I will try to do so.

will come back soon.

[Weelcup]

Re: very challenging issue! lenovo G50-80?

i could not figure out the short place. But what made me confused is that there is no short to ground in the line from +VL to the IO chip. however, according to the schematics then it had to. but in reality all other +VL signals are shorted except for the Signal to the IO.
but i could not figure out the place of the resistant RE1 and RE3 to check if RE1 is the cause.

[JaroTech]

Re: very challenging issue! lenovo G50-80?

Maybe that's because the motherboard is revision 1.0 and the schemas are revision 0.4, they made some changes.