Need some help with HP 250 G3 dead Motherboard

[eng.jaudat]

Hello my friends,
i attached the schematic, my problem that there is no any Voltage on the gates on the power mosfet shown in the figure:



Which IC should create that missing voltage?
and whats the expectations of the problem?

thank u so much.

[khaahk]

Re: Need some help with HP 250 G3 dead Motherboard

BQ24738 should create the 25V to open the PQ101 & PQ103. In case of overcurrent it might turn off the fets to protect circuit. Measure resistance at B+, check the fets and then replace BQ24738. Does the board work from battery?

[tibd]

Re: Need some help with HP 250 G3 dead Motherboard

Have you tried with a known good power supply?
What is the voltage at pin 12?

[eng.jaudat]

Re: Need some help with HP 250 G3 dead Motherboard

BQ24738 should create the 25V to open the PQ101 & PQ103. In case of overcurrent it might turn off the fets to protect circuit. Measure resistance at B+, check the fets and then replace BQ24738. Does the board work from battery?

My friend,

sorry, which resistance u mean? is it PR103? m trying to replace BQ24738, but its the same problem, i'm not sure if the board work from battery, i don't have charged battery, i will try it within a few hours.

[eng.jaudat]

Re: Need some help with HP 250 G3 dead Motherboard

Have you tried with a known good power supply?
What is the voltage at pin 12?

Yes my friend, my power supply is very good.

i have just 0.4 VDC at pin 12.

[khaahk]

Re: Need some help with HP 250 G3 dead Motherboard

Resistance from B+ relative to gnd to see if there is a short at B+ rail. Have you checked the FETs PQ101 and PQ103?

[eng.jaudat]

Re: Need some help with HP 250 G3 dead Motherboard

Resistance from B+ relative to gnd to see if there is a short at B+ rail. Have you checked the FETs PQ101 and PQ103?

there is a short between B+ and Gnd, FETs PQ101 and PQ103 chedked, and they are good.

[fddizon]

Re: Need some help with HP 250 G3 dead Motherboard

do you have dc bench PS?

[eng.jaudat]

Re: Need some help with HP 250 G3 dead Motherboard

do you have dc bench PS?

honestly i don't. but i used a genuine HP charger.

[ridamouh159]

Re: Need some help with HP 250 G3 dead Motherboard

have you changed PQ103 ؟

[eng.jaudat]

Re: Need some help with HP 250 G3 dead Motherboard

have you changed PQ103 ؟

Yes my friend i changed it. same problem

[aedler]

BQ24738 should create the 25V to open the PQ101 & PQ103. In case of overcurrent it might turn off the fets to protect circuit. Measure resistance at B+, check the fets and then replace BQ24738. Does the board work from battery?

Hi, i have same problem , the board work from battery if i remove the lcd connector ,PQ101 & PQ103 are not shorted b+ not shorted too.can you help me please?

[Mazorca]

Re: Need some help with HP 250 G3 dead Motherboard

Those are N-mosfets, and they open (work) when the voltage Vgs is lower than Vin, around 10v or so. Check that. Did you physically remove said mosfets? Only good way to test them.

[Mazorca]

Re: Need some help with HP 250 G3 dead Motherboard

Those are N-mosfets, and they open (work) when the voltage Vgs is lower than Vin, around 10v or so. Check that. Did you physically remove said mosfets? Only good way to test them.

OOPS, Wrong advice. For N-mosfets, Vgs should be higher, usually 32v.

[muanpuia]

Re: Need some help with HP 250 G3 dead Motherboard

Force with a high amperage power supply to see if something becomes hot. It might be caps