Dead Thinkpad E15, hissing noise from BQ25710

[badcappo]

Hello there, got a Thinkpad E15 on the bench, almost no vital signs. Only things: Power button white LED flashes several times when USB-PD gets connected (number of flashes varies from three up to twelve times, sometimes no reaction at all). Battery charge indicator LED stays orange. Most interesting is hissing / whining sound from Battery Charge Controller IC BQ25710 on the keyboard side of the main pcb. Board fuses tested and intact, no shorts found so far. BQ25710 is also the only thing on the board to become warm in thermal image (below 70 °C). Thanks for any hint.

[kotel studios]

That would suggest the BQ25710 being bad. Check if all the input/output voltages are correct. And you might also see if the laptop tries to power on without that chip. Not sure if it's not gonna damage anything if it's not there....

[Sametbey]

If the charge light is on, this indicates that the Bq24710 and IO circuit are working. The 3.3v line is intact. BIOS can be tried.

[kotel studios]

Yeah but I don't think BQ25710 should get that hot. I am not a specialist, but 70C doesn't sit quite right with me....

[Sametbey]

There is a diagram on the forum. The charging chip and other operating voltages should be measured.

[badcappo]

Thanks for the input. The hissing sound still makes me wonder, has anyone experienced this? It sounds exactly (!) like these small flash discharges when you're touching a plasma globe and it comes right out of the chip (pressing it gently with a screwdriver has no effect).

[ajgae]

Ive heard hissing sounds from bad components before, specifically I once saw a board that had soldered-on RAM and one of the RAM chips was hissing impressively loudly and getting incredibly hot. Covering it with IPA revealed a hot spot in a corner of the chip which I figured just meant the chip was dead. If a mosfet is hissing I can't imagine it can be healthy

[badcappo]

Yeah, might there be some kind of a spark discharge happening inside the chip? This could also explain the hot surface temperature I assume (?). It does sound like these rather new plasma arc lighters...100% the same hissing noise but way more subtle (I have compared it next to each other).