As I’ve been doing a number of board level repairs this year, I’ve decided to collect my notes here as they might help others to troubleshoot or to give to repair companies as a guide of where to look.
Leftmost column of keys nonfunctional.
Probable cause: Short between power jack and keyboard switch.
Replaced keyboard with new keyboard (QWERTY). Kept old for refurbishing (MCU change).
i.MX8MQ SOM was damaged – no boot. Maybe only voltage regulators burned out. Stored for future repair.
Replaced i.MX8MQ SOM with new one.
Performed safety modification to prevent future problems: MNT Reform: First EU Batch? Do this safety modification
Tested all features with R2Test SD Card.
Cleaned up and put back into sleeve that it came in.
Cleaned keyboard and exchanged keycaps to MBK model (QWERTY).
Cleaned unit with compressed air.
Replaced missing screws.
Replaced all 8 battery cells (7/8 were dead).
Replaced discharge resistor R29 (it was exploded). 10 Ohms.
Performed charge control modification with a bodge wire (see MNT Reform R-2 Motherboard Update 2021-04-19).
Performed safety modification on power jack (see MNT Reform: First EU Batch? Do this safety modification).
Upgraded motherboard firmware to R2/20210419
Upgraded keyboard firmware to R1/20210419
Had 2 bad measurements on LTC sense resistors:
Decided to desolder and exchange LTC6803-4 chip. This fixed the problem. The chip was faulty.
Performed charging test. Cell voltages nominal, charger correctly finished at top end.
Symptom: Internal display doesn’t work after a US repair company, PSI, originally fixed a problem with the power circuit. Then, they exchanged U10 with a new one (my suggestion). This did not fix the problem. Customer sent the board to us for inspection.
- The problem is that regulator U13 does not work. It supplies 1.2V for the eDP converter and the USB hub. The repair company did not check for/find this problem.
- U13 outputs only 0.025V
- LPCs 1V2_PWR_EN line is low, so it doesn’t enable U13 or U13 pulls the line low very hard
- U13 is the culprit. I removed the 0R on its enable and it is now high on the LPC side.
- Replacing U13 fixed the display (and i guess USB).
- I have also tested both pcie slots, ethernet, audio, battery charging and discharging. Looks all good.
Symptom: Internal display stopped working. In dmesg it looks like eDP link failed.
- The problem was a faulty U10 (SN65DSI86IPAPQ1). This is rare. Maybe the eDP connector was reversed or there was a static discharge.
- Swapping U10 with a new one fixed the problem.
Symptom: Motherboard burns a lot of power and generates heat immediately when on wall power.
- It turns out Diode D5 was shot. This causes some of the buck/boost MOSFETs to get very hot.
- Removing D5 fixes the problem. According to LTC4020 manual, this diode is optional, so leaving it off.
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.
- 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.
- SD Card boot OK
- eDP display OK
- HDMI OK
- PCIe 1+2 OK
- Ethernet OK
- RTC OK
- UART 1 OK
- USB OK
- SYSCTL OK
- 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.