Lenovo b450 no power help

[rickybucalan]

hello everyone....

im just having a problem with this mobo.

there is no 3.3v and 5v alw in Coil. but in DC/dc IC is Present
i dont know why it is not going to coil.

i can't find the issue...

i check all coil no shorted

flash bios still no power

checked power switch ok.

19v present

clean mobo still no power

reflow vga chips still no.

pls help guys...

[rickybucalan]

Re: Lenovo b450 no power help

bios file guys?

[electronica]

Re: Lenovo b450 no power help

1mn of searching on google
bios : http://www.alexlaptoprepair.com/wp-c...enovo_b560.zip
schematic:


flash the EC_bios first .

[electronica]

Re: Lenovo b450 no power help

the EC is a common problem in this model .

[BlueMidnight]

Re: Lenovo b450 no power help

U47 has 4 outputs:
3V/5V LDO (low current)
3V/5V switching/buck (high current)

Your LDO outputs are working. Your switching outputs are not. The LDO outputs do not go through the coils.

It's a good idea to completely investigate U47 before assuming what the problem is. In fact, I would just check the voltages on all 24 pins and then compare that to the schematic.

The main question is: Are the switching outputs enabled? (pins 1 and 6 high). If they are enabled but not outputting voltage, then the problem must be in or around U47. For example, U47 itself might be bad, one of the 4 MOSFETs (U22, U23, U28, U29) is bad, or there is a short on one of the outputs.

If the outputs aren't enabled, then check the S5_ENABLE signal. You should only worry about the EC in this case if there is no S5_ENABLE signal.

[rickybucalan]

Re: Lenovo b450 no power help

1mn of searching on google
bios : http://www.alexlaptoprepair.com/wp-c...enovo_b560.zip
schematic:


flash the EC_bios first .

i think there is only main bios of this mobo. can't find EC bios.

[ridamouh159]

Re: Lenovo b450 no power help

there is only main bios of this mobo with 2mb

[rickybucalan]

Re: Lenovo b450 no power help

there is only main bios of this mobo with 2mb

thanks buddy but it won't works too... still no power.

[rickybucalan]

Re: Lenovo b450 no power help

U47 has 4 outputs:
3V/5V LDO (low current)
3V/5V switching/buck (high current)

Your LDO outputs are working. Your switching outputs are not. The LDO outputs do not go through the coils.

It's a good idea to completely investigate U47 before assuming what the problem is. In fact, I would just check the voltages on all 24 pins and then compare that to the schematic.

The main question is: Are the switching outputs enabled? (pins 1 and 6 high). If they are enabled but not outputting voltage, then the problem must be in or around U47. For example, U47 itself might be bad, one of the 4 MOSFETs (U22, U23, U28, U29) is bad, or there is a short on one of the outputs.

If the outputs aren't enabled, then check the S5_ENABLE signal. You should only worry about the EC in this case if there is no S5_ENABLE signal.

thanks. i did replaced U47 but it still dont work. i guess it not the problem.
about 4 mosfets i didn't find any short with them.

[electronica]

Re: Lenovo b450 no power help

i think there is only main bios of this mobo. can't find EC bios.

yep ..sorry i mad a mistake

[BlueMidnight]

Re: Lenovo b450 no power help

Soldering should be avoided whenever possible. It might make things worse by accident. Or if you put a new component in a bad circuit, it will just fry the new component. Guessing is rarely required. You need to find the problem logically. Start by measuring the voltage on all the pins. Especially on 1 and 6 in this case.

MOSFETs can short in 3 different ways: source-drain, gate-source, and gate-drain. Remember to test for all 3.

[rickybucalan]

Re: Lenovo b450 no power help

Soldering should be avoided whenever possible. It might make things worse by accident. Or if you put a new component in a bad circuit, it will just fry the new component. Guessing is rarely required. You need to find the problem logically. Start by measuring the voltage on all the pins. Especially on 1 and 6 in this case.

MOSFETs can short in 3 different ways: source-drain, gate-source, and gate-drain. Remember to test for all 3.

i don't know what to say.. i are so amazing Bluemidnight.... thank u so much for your help...

i miss that to test gate-source and gate-drain. i found 2 mosfets short on (gate-source).

but after removing one mosfet and test it wasn't short. so i put it back then tried its works... its could be bad contact may be.

i learned lot from u bluemidnight thank u again.....

God bless.

[NIKHILKYOHANNAN]

Re: Lenovo b450 no power help

hello everyone....

im just having a problem with this mobo.

First i got the problem not powering on and i found one SMD capacitor Shot to ground which is DCBATOUT signal,After replacing this capacitor I got the dispaly.but it motherbored now showing Auto power on. Cmos battery voltage has 3.3v also clear the Cmos Battery,but not succeed.

hope anyone can help me..T I A