[SOLVED] Lenovo E15 G4 charging at 5 volts

[247it]

Hi everyone, I hope someone has some pointers for me, for fun I'm trying to repair USB C charging on a Lenovo E15 G4 laptop, I brought this back from work as it was written off, I successfully replaced the USB C port some time ago, however it was broken again by the end user, this time the port was twisted off the board but the pads survived,
I have installed another port but the charger never gets the ok from the PD chip (tps65994ae) to go to 20 volts, it does charge slowly using the boost converter to step up the charging voltage but takes hours, voltages present on the PD controller are 5v, 3v and the CC lines are 0v to 1.6v depending which way the power plug is connected, is it worth changing the protection IC? i think thats what sends the 1.6V to the PD chip from the charger so im asuming its ok,
I have changed the PD chip twice, both chips came from AE so not sure of the quality, the second chip I got looked like the original with the correct fonts etc, the first PD chips markings looked different and hard to read,

Any advice gratefully received,

[FriedFred]

If the current is very little, probably the battery itself is damaged. Usually you can measure the current indirectly over the current measuring resistor. While the battery is charged with that little current, you can force to flow a higher current with a resistor as a bypass to the battery. With 12 Ohm, the bypass current is 1A. But it needs 12W. Or you use an electronic load. In that way, you can test the current flow with several Ampere. But maybe it's easier to use another, known-good battery first.

[FriedFred]

I forgot: If the battery is full, also only a little current flows, the trickle charge current.

[247it]

Thanks FriedFred, battery seems ok, holds a decent charge anyway, just takes forever to charge at 5 volts 3 amps, even if the battery isnt installed the voltage from the charger never goes over 5 volts, should be 20 volts at 3 amps, tried different chargers and a big power bank but 5 volts is the max that the power supply goes to, its a real tricky one but im enjoying learning, thanks for your input

[FriedFred]

To a battery get charged, it's necessary that the input voltage is higher than the nominal voltage of the battery.
Without the battery plugged-in, there shall be a voltage of at least 19V anywhere on the board.

[247it]

Thanks FriedFred, the battery is 11.1V there is a boost converter on the mainboard, 5 volts on the usb c (on the meter) 12v charges battery, not sure why the buck-boost, maybe to suppy the battery mosfets gate with more than 20 volts when running corrrectly,

anyone know the buck-boost purpose?

[FriedFred]

It's because you can use any voltage from 5V to 20V on the USB-C input. For example, a real USB-C charger will supply 19V. But a little, old USB-C charger will supply 5V only. Therefor it's necessary to have a buck-boost converter for the 12V-Battery.

[247it]

Thanks FriedFred, makes sence, i have learnt afterwards the PD chip has a charge pump of its own, it looks like that is used to raise the gate voltage higher than 20V so the MOSFET conducts correctly, still stuck at 5v at the moment, i have a new PD chip on the way plus a new port protector IC just in case, everything else seems ok,

[mon2]

CC1/CC2 pins are used by the PD to negotiate the power delivery contracts. Remove all power. Meter in DIODE mode. Red meter lead, yes red to ground.

Black meter lead to the CCx pin to test. Post each measurement. If the measurement is very low and close to 0v then the pin is indeed shorted (likely the protection ESD diode on this line). Based on earlier posts, the protection diode is most likely ok.

The power up default of all power delivery controllers is 5v on Vbus. After a proper handshake, the PD adapter will offer the 20v on Vbus.

You can use low cost PD bus analyzers / tail tools to monitor if the PD controller is working or not and also the pd contract being selected.

[247it]

Thats great info, thank you, the PD chip is out at the moment, i hope to get the new one Sunday or Monday, I'm seeing 5v on TPS65994AE BGA pad - pin H8 - TBTA_VBUS20,

i do recall seeing 1.6V on one CC line and .4V on the other, spin the USB C plug over and the voltages reverse,

ill have a look at the analysers, sounds like an interesting tool to have,

i had a slight concern regarding EEPROM that the PC chip connects to (CAT24C256WI) i took it out and read it so assume all good, i may be getting ahead of myself though
appreciate the help!

[247it]

Hi mon2, new PD chip is in, in diode mode red to ground black to cc1 and cc2 reads .432 there is 5v on the vbus,

[247it]

If anyone is interested, this problem was a corrupt EEPROM, there is some talk that the PD controller (TPS65994) doesn't need programming, it does 100%, if the code in the EEPROM goes bad, the PD chip will not start and is inaccessible,

Massive credit to SMDFlea, thanks man! donation to the site made, link to the solution here.