hp elitebook 840 g2 power button voltage drop 1.8v

[dqtech]

power button only read 1.8v instead of 3.3v....when i plugged in charger, this laptop will turn on it self for few second (current read normal over than 600+), then will stay remain only 20++...

i've check on ec pin 73 (power button) also read 1.8v....is that could be faulty EC chip?

i have another motherboard same like this one and check on EC, pin 73 got 3.3v

[dqtech]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

board number 6050a2637901-mb-a02 CHICLET....here the schematic...but only found COMET version

Link to schematic - https://www.badcaps.net/forum/showthread.php?t=85724

Reminder: rules and organization of this section
- https://www.badcaps.net/forum/showthread.php?t=117483
.

[mcplslg123]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

pin73 should be 3.3V. What is the resistance to GND on pin73? CN9100,pin3/4 voltage? Is powerbutton on a separate board? If yes,disconnect it and then measure pin73 voltage again. I dont think kbc is faulty at this stage.

Pin68 of kbc-What's the voltage here?

[dqtech]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

pin73 should be 3.3V. What is the resistance to GND on pin73? CN9100,pin3/4 voltage? Is powerbutton on a separate board? If yes,disconnect it and then measure pin73 voltage again. I dont think kbc is faulty at this stage.

Pin68 of kbc-What's the voltage here?

right now power button no voltage appear...

resistance on pin73 = 67k ohm
voltage on pin68 = 3.3v

cn9100 is separate board power button....pin 3 voltage pulsing 0v-1v and pin 4 read 3.3v

disconnect cn9100, pin73 also read 1.8v

[dqtech]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

maybe pulsing came from this diode

[Udemzy]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

Search for D100 there are some resistors close to the empty diode space, one of the resistor will read 3.3v at on side and the 1.8v at the other pin, same voltage on your power button, replace the the resistor with a 1k ohms resistor and you're good to go.

This will help to safe the sio

[dqtech]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

Search for D100 there are some resistors close to the empty diode space, one of the resistor will read 3.3v at on side and the 1.8v at the other pin, same voltage on your power button, replace the the resistor with a 1k ohms resistor and you're good to go.

This will help to safe the sio

thank you for your reply sir...i did replace resistor 100k ohm with 1k ohm that i mark on picture...right now when i plugged in charger, this laptop turn on it self...but power button still no respond....i check on powerbutton pin3 still 0v

[dqtech]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

pin 73 on sio right now 3v...before only 1.8v

[dqtech]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

thank you for your reply sir...i did replace resistor 100k ohm with 1k ohm that i mark on picture...right now when i plugged in charger, this laptop turn on it self...but power button still no respond....i check on powerbutton pin3 still 0v

this laptop turn on it self only without cmos battery....when i attached cmos battery right now it wont turn on because no respond from power button...0v on cn290 pin 3

[mcplslg123]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

Remove the power button board and short pin73 to GND(Cmos cell inserted). Does it turn on?

[dqtech]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

Remove the power button board and short pin73 to GND(Cmos cell inserted). Does it turn on?

yes it does turn on sir when i short to ground pin 73

[mcplslg123]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

This proves that your RTC circuit is fine. You can either replace the power button board or isolate the power button pin from PCB and make a jumper between SIO,pin73 to power button.

[dqtech]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

This proves that your RTC circuit is fine. You can either replace the power button board or isolate the power button pin from PCB and make a jumper between SIO,pin73 to power button.

do you mean make a jumper from SIO pin73 to CN290 pin 3?....because i tried replace power button board but also no respond when press switch button....cn290 pin 3 no voltage at all

[dqtech]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

i make a jumper from D100 to pin 3 CN290, now everything working fine....powerbutton all running good....but do you have any other solution to resolve this issue without make a jumper like this

[mcplslg123]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

Its difficult to pin point the root cause of this malfunction without having the mb in hand. I tried my level best to give an alternate way to make it work.

[dqtech]

Re: hp elitebook 840 g2 power button voltage drop 1.8v

Its difficult to pin point the root cause of this malfunction without having the mb in hand. I tried my level best to give an alternate way to make it work.

okay thank you sir