Lenovo Legion 5 Pro 16ACH6H Type 82JQ – Shorted EC Chip

Hello,

On pressing the power button, keyboard backlight illuminates and the fans spin for a couple of seconds, then go off. Light on power button stays on. The cycle then repeats.
I discovered that the EC chip has a crack in the top. It is taking 400mA at 0.8v. Also, the capacitors surrounding it read as shorted to ground.
I’ve removed the chip and the capacitors are no longer shorted to ground.

Before replacing the chip, I would like to try and find what caused the chip to die in the first place, as I’m worried that if I solder in a new chip, it will suffer the same fate as the original one.
With the chip removed, I’ve checked all of the pads for resistance to ground. The only pads which produce 0Ω are numbers 1, 27, 49, 75, 91 and 104, which is correct as they are all ground pins.
I’ve checked voltages at the buck converter (Richtek RT6585C) and have 20.5v on pin 12, 3.3v on pin 3 and 5v on pin 13, which all seems to be fine.

What other checks should I be carrying out before installing a new EC chip?

Motherboard number is HY660 HY661 HY561 HY572 HY56C HY57K NM-D562 Rev 2.0.

Thank you.

Check the DC socket if there are any signs of damage, crack etc. Most often the KBC dies when there is problem in the DC socket area. Also check the power supply socket.

There is also a slight possibility of PCH\CPU damage when DC+ gets shorted to ACID

You can try to supply 20.5V on the DC jack to check if the APU gets hot even without a working KBC. If it does, then damage to the PCH part of the APU is very probable.

Have checked the DC socket. Everything looks good, no signs of cracking, burning or damaged contacts. Have checked inside the port using a microscope.

Applying 20.5v at the DC socket with my bench power supply, the current switches between 20mA and 0 every second. I can also hear a very faint ticking sound coming from the board. The APU remains cold.

If I apply 0.8v onto any of the coils above the APU, I get a current draw of 410mA, but again the APU remains cold.

Update - I've remember that you can't power Lenovo Legions from a bench power supply because of the charger id pin. I need to trick the board into thinking a charger is connected

If there are no sings of damage to the DC socket then solder new KBC chip and then proceed further. When You solder new KBC make measurements of 3.3V line before connecting PS. KBC supplies a lot of crucial signals, so diagnosing without it can give strange results.

And yes, for this Lenovo model, You need a 230W charger or an adapter to the laboratory PS. You can build it Yourself using a resistor between GND and ID pin. Be sure to use a cable/DC socket without resistor inside.

Resistor values: post276130.html#p276130

Received the new EC chip today and have soldered in place. The seller has programmed the chip to suit the board. What measurements of the 3.3V line do I need make?

You have previously mentioned, that the short on 3.3V line was gone, when You desoldered the KBC. So the next thing would be to measure 3.3V coil to the ground when new one is soldered and also the capacitors supplying 3.3V to the EC chip.

If the resistancje is higher than <20kΩ on the 3.3V line, then You can try to power up the board and check if it works. Remember to wait some time after supplying power, as the new chip will have to get along with the rest of the board

Resistance of the 3.3v coil to ground is 2.78kΩ. The capacitors of the 3.3v supply to the EC chip are measuring 378kΩ, which is the same measurement I get on pin 3 of the buck converter.

Actually for this board this resistance seems fine - test the laptop

Bad news, I'm afraid, the same problem as in my first post is still happening

When removing the board, I could smell burnt plastic. The capacitors on the 3.3v supply are all reading as shorted to ground. The new EC chip shorted out the second I turned the power on. I checked all 128 pins after soldering the new chip and the only 0Ω values were the same as stated in my first post. I checked every pin to make sure there were no bridges to adjacent pins and also checked that every pin was securely soldered to its pad.

I've removed the chip and the 3.3v line is no longer shorted.

I'm wondering if the new chip I received was actually faulty or maybe even a fake. It looked brand new, all the pins were clean with no evidence of ever being soldered. I've attached a photo of the chip after I had soldered it to the board. I used a soldering iron to do this, rather than hot air gun. I do have another identical chip, which I will solder in place tomorrow.

Would it be possible to inject 3.3v using my bench power supply, with a current limit set at 100mA, to see how the chip reacts? I'm not sure what current the EC chip should draw during normal operation, but the datasheet for the buck converter states a minimum output of 100mA and typical output of 175mA.
Could incorrect firmware in the chip cause something like this. The seller did ask for the laptop model number and motherboard markings to ensure the chip was programmed correctly. Unfortunately, I don't have a means of programming EC chips myself yet.

Leave the damaged EC chip on the board and measure the following resistances to ground:
- On coils PL6201, PL6202.
- On pins 3, 13 of chip PU6201.

With the damaged chip, the resistances are as follows:

PL6201 = 642Ω
PL6202 = 5.44kΩ
PU6201 pin 3 = 10Ω
PU6201 pin 13 = 648kΩ

Open the jumper PJ6201 and measure the voltages to ground on pins 3, 13 pf chip PU6201.

With jumper PJ6201 open, voltage to ground at pin 3 is 3.3v, pin 13 is 5v.

Replace the KBC chip again, close the jumper PJ6201 and remeasure the resistances from the post #11.

With the new KBC, resistances to ground are as follows:

PL6201 = 2.78kΩ
PL6202 = 5.4kΩ
PU6201 pin 3 = 370kΩ
PU6201 pin 13 = 654kΩ

Now open the jumpers PJ6205, PJ6206, PJ6207 and connect the power supply to the board. Remeasure the voltages to ground on pins 3, 13 of chip PU6201.

Voltage on pin 3 is 3.3v. Voltage on pin 13 is 5.15v.

Also measure the voltages to ground on coils PL6201, PL6202 (with the jumpers PJ6205, PJ6206, PJ6207 opened).

PL6201 = 3.38v, PL6202 = 5.16v.

Close the jumper PJ6206 and remeasure the voltages to ground on coils PL6201, PL6202.