please help friends Thinkpad T490 dead loses POWER SHUTDOWN voltage, thank you

[fredyjbi]

Please help sir, I included a schematic of the T490 nm-b901 completely dead, after I checked, I lost the voltage -PWRSHUTDOWN 0v which should have been 3.3v, which was produced by the BD4179MWV chip, thank you

F9502 20v
UTE1B
pin 44 TE_BAT_VOLT 12v
oin 43 3SW_OFF# 19.8v
pin 45 VREGIN20 19.8v
pin 47 VCC3SW 3.3v
pin 55 SHUTDOWNIN# 3.3v
pin 54 TH_DTCT 3.3v

-PWRSHUTDOWN missing 0v resistance 380k
R9512 pin 2 3.3v pin 1 0v resistance 380k

https://www.badcaps.net/forum/troubl...rdview-request

[mon2]

To confirm, AFTER the shutdown signal being low, you still have 3v3 on R9512, pin # 2 ?

What is the history of this machine? BD4179MWV has SPI lines linked to the EC -> check them for a voltage. Also check the SPI lines without power, in DIODE mode. This is to confirm the lines are not damaged and that this ASIC is able to extract the required firmware from the EC (or does it supply it to the EC - not sure?). On SPI, there will always be a bus master.

Suggest to remove all power -> meter in resistance mode -> measure the resistance to ground on each and every inductor. Hunting for a low resistance (short) condition which can result in an excessive current draw and causing this event.

[fredyjbi]

To confirm, AFTER the shutdown signal being low, you still have 3v3 on R9512, pin # 2 ?

What is the history of this machine? BD4179MWV has SPI lines linked to the EC -> check them for a voltage. Also check the SPI lines without power, in DIODE mode. This is to confirm the lines are not damaged and that this ASIC is able to extract the required firmware from the EC (or does it supply it to the EC - not sure?). On SPI, there will always be a bus master.

Suggest to remove all power -> meter in resistance mode -> measure the resistance to ground on each and every inductor. Hunting for a low resistance (short) condition which can result in an excessive current draw and causing this event.

Thank you sir for your help, this board came dead and clean, sir on R9512 pin 2 I have 3.3v and 0v on pin one, the 33k resistor R9512 is fine, sir what SPI signals should I check thank you , I compared it with a normal board which is suspicious is pin 54 TH_DTCT 3.3v on a normal board the measurement is 0.5v, thank you sir for your interest in helping me

[mon2]

TH_DTCT may be 'thermal detect' signal but is only a guess.

Update - guess is correct - this line is connected to thermistors on the board.







See attached.

[mon2]

Check this thermal sensor line in DIODE mode. Remove all power. Meter in DIODE mode. Red meter probe to ground. Black onto this pin on the IC. What is the measurement?

Compare to the known good board. You may have a defective thermal sensor. Perhaps you can rig it by grounding this line for a quick test.

[fredyjbi]

Check this thermal sensor line in DIODE mode. Remove all power. Meter in DIODE mode. Red meter probe to ground. Black onto this pin on the IC. What is the measurement?

Compare to the known good board. You may have a defective thermal sensor. Perhaps you can rig it by grounding this line for a quick test.

Sir, my normal board measurement results are 718, the dead board is 718, the results are the same, thank you

[fredyjbi]

Sir, if I try to measure TH_DTCT avometer scale resistor black probe groud red probe pin 54 TH_DTCT the results are different, the normal board shows 6.6k and the dead board shows 3.4m, thank you