After replacing sr pro 4 LCD,won't turn on battery mode unless plug it

"We got a couple of these SP4's in from repair shops where battery stopped working after screen replacement. Most of them had a blown diode in the charger circuit, another one a blown FET. We guessed that the display wasn't switched off when taking it off, causing the LCD backlight power buck converter to spike, but according the repairshops who sent them this was not the case. So why this is happening, we got no clue at all.

Done an SP3 as well, same sympthoms. Only way to solve it on the SP3 was to replace the battery AND the charge controller chip.

Kinda rubbish, these SP's if you ask me.

Theo | Logicboard Repair

Update (01/23/2018)

If you encounter this problem, check the two Skottky Diodes in the picture. (40 Volts / 5A). Voltage over the diode from anode to kathode should be around 0,2V. If higher, then replace. (Needless to say you have to measure this in Diode mode, with a disconnected battery). Also we encountered problems where 1 of the FET's on the control board of the battery itself went into a latch-up state. This can be solved by shorting drain and source shortly. (Be carefull!) Hope this helps someone.

Theo | Logicboard Repair

Update (10/04/2019)

We think we found out the cause of this strange fault. The capacitor in the blue circle is very big, the slightest pressure on the metal shield cover will shortcut the capacitor and cause this failure. Make sure that you do not put any pressure on this shield, remove it and place some capton tape on the inside of the shield to make sure the capacitor cannot be shorted anymore. Again, hope this helps someone!

Theo | Logicboard Repair"

Sounds like a problem with the power manager. Do a hard reset by holding the volume up and power at same time until the machine turns off. Wait a few seconds and turn it on. Hopefully, it will work normal after this.

"Also had the same issue.

Replaced LCD and doesnt turn on.

Plugged in and turns on normally. Works perfectly however as soon as remove charger, turns off.

For sure, this is not battery issue, as already tried replacing the battery.

Met last week with another tech, and he had couple of surface with exactly same issue."

"this is my device

check diodes 1: is 1

check diodes 2: is 192"

The battery needs to be replaced, if you put the device in a heater to remove the screen then the heat likely damaged the battery

I wish someone would solve this problem, which I also have.