Upper left battery on OLED discharging faster

MNT Reform
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Hi,
The mainboard mod MNT Reform R-2 Motherboard Update 2021-04-19 has been done. Keyboard & LPC firmware was updated to the last version in the sources. The upper left battery on the OLED dropped voltage faster than the other ones. I switched the right battery of the left battery module with the left one of the module after measuring the other ones. I noticed a voltage drop of 0.2V from OLED display to the real battery. Battery to GND 3.2V - J2 (BATLEFT) second PIN to GND 3.1V - R31 right pad to GND 3.0V. I reworked J2 connector and R31 resistor (possible cold solder joint) with no result. Measured J2 second pin to R31 right pad - 0 ohm. Everything after disconnecting batteries :slight_smile: (I think I should mention this :sweat_smile:) After connecting the batteries I noticed that resistor R32 always gets hot when connecting the BATLEFT connector. After checking the schematics I checked Q12 (with diode test and batteries disconnected). R24 on the gate was shorted to GND on the LTC6803 balancer side. A first rework on the LTC6803 pins 23-27 with soldering only the pins did not change anything. A visual inspection did not show any shorts/or bridges from PIN 25 to PIN26 etc. After putting a fat blob of Sn63 / Pb37 leaded solder over these pins and removing it with solder wick (I think you should be experienced in soldering when trying this) solved the connection of PIN25 on U4 to GND problem. Before I connected the batteries I did a visual inspection of the reworked U4 chip :sweat_smile:.

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And now everything seems to work as expected :nerd_face:

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So, what did I learn today?
After assembling the reform2 and connecting the batteries I did feel some heat from the balancing part of the board. While charging it there was excessive heat from the resistors and mosfets. I was thinking that’s because of the balancing process or a bad thermal design (sorry :see_no_evil: ).
If R32 or Q12 are to hot to touch (R25-R32 and Q5-Q12 are for balancing) and you think the right cell of the left battery module (upper left battery indicator on the OLED) is damaged you should check R24 (upper pad) to GND.

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