Motherboard repair on 2022-11-03
This one was complicated, took at least 4 hours.
Symptom: system uses 12W of wall power when powered off (no CPU module inserted). Q17 gets very hot, turns some sprinkled IPA into steam. owner already removed D5, a usual culprit, but it did not fix the issue.
initial repair:
- swapped Q17
- swapped U2
- swapped Q2
- removed D7, D6, D4. short is gone, but LTC (U2) not operational
- put D6, D4 back in → short is back
- measured 2ohms across Q2, that’s bad
- inducing power at 30V_GATE works fine, LPC is functional
- so the problem is close to buck/boost of LTC
- inducing 12V at BAT1FUSED also works fine, LPC detected on USB
- so the problem is close to the input stage of LTC
- candidates: Q15, Q1
- 120 ohms to gnd on gate of Q17. unlike on reference board
- replaced Q17 again. it was shot again! problem is gone.
- put in new D7. still fine.
- repaired HDMI connector with dental tools.
- replaced partially melted connector J23.
tests:
- SD Card boot OK
- eDP display OK
- HDMI OK
- PCIe 1+2 OK
- Ethernet OK
- RTC OK
- UART 1 OK
- USB OK
- SYSCTL OK
battery tests:
- highest cell (BAT1->2) measures 0. drop of 3V on F1.
- fuse F1 is shot!
- replaced with new fuse.
- now another cell measures 0. R14 measures 6V, R15 measures 6.5V, which is odd.
- this is fine, it was just the protected BB closing off one cell. opens after applying charge.
- cells are charging normally.
- LPC FW updated to latest version.
- repair concluded.