• Lenovo Thinkpad T420i can't start

It is currently 14 December 2024, 07:44

Lenovo Thinkpad T420i can't start

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  1. Topic title should contain: the device's manufacturer, full model and the brief description of problem.
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#1 Lenovo Thinkpad T420i can't start

by cygron • 5 August 2024, 09:30
Model : Lenovo Thinkpad T420i
Board id : NZ3 UMA Rev: F M/B LNVH-41-AB5700

Laptop came with 19V line short. I found shorted capacitors (C1316, C1011) and replace with good capacitors. Now 19V line is ok. 3V 5V is ok. PWRSWITCH is ok. Pin 19 of connector J7 (PWRSWITCH) is 3.37V. U23 pin 23 (PWRSW) is alsop 3.37V (without press power key) and 0V (when press power key). But laptop can't open. There is no amp comsumption. BIOS flashing can't solve the problem. Need help.

Re: Lenovo Thinkpad T420i can't start

by Google Adsense [BOT] • 5 August 2024, 09:30

#2 Re: Lenovo Thinkpad T420i can't start

by matic • 5 August 2024, 13:19
Hello!

- Measure the voltages to ground on pins 6, 13, 19, 20, 24, 27, 51, 75, 76, 126, 134 of KBC chip U23.
- Measure the voltage to ground on pin 33 of KBC chip U23 in the following cases:
a) Power button released.
b) Power button pressed.

#3 Re: Lenovo Thinkpad T420i can't start

by cygron • 5 August 2024, 15:01
U23 pins are
Pin 6 - 0V
Pin 13 - 1.5V
Pin 19 - 3.3V
Pin 20 - 0V
Pin 24 - 0.12V
Pin 27 - 0V
Pin 51 - 0V
Pin 75 - 3.37V
Pin 76 - 3.37V
Pin 126 - 0V
Pin 134 - 0V

Pin 33 is 3.37V with or with press power key from Keyboard. When pin 19 of connector J7 short to ground Pin 33 is 0V.

#4 Re: Lenovo Thinkpad T420i can't start

by matic • 6 August 2024, 14:16
- Measure the resistance to ground on pin 27 of KBC chip.
- Measure the voltages to ground on both pins of resistor R831.

#5 Re: Lenovo Thinkpad T420i can't start

by cygron • 6 August 2024, 17:31
Pin 27 - 17K
R831 pin 2 is 3.37V and pin 1 is 0V

#6 Re: Lenovo Thinkpad T420i can't start

by matic • 13 August 2024, 08:39
Check the resistor R831 (10kΩ).
Are the resistors R955, R971 physically present on your board?

#7 Re: Lenovo Thinkpad T420i can't start

by cygron • 15 August 2024, 10:51
R831 has right value (10K). Resistors R955 and R971 are physically present on board. Both are 0Ohm resistors.

#8 Re: Lenovo Thinkpad T420i can't start

by matic • 12 September 2024, 13:02
- Measure the voltages to ground on both pins of quartz Y6 preferably with oscilloscope. If you don't have it, measure with a multimeter.
- Measure the voltages directly on capacitors C285, C459.

 This topic is marked as ARCHIVAL. Please only reply if your message contains the solution (Terms and Conditions p. 12.1).
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