Broke off RTC Coin battery pin on HP EliteBook 840 G1 - Operating Systems do not load or install

[nerdmafia]

Hi first question posting here, but no need to go easy on me!
I have an HP EliteBook 840 G1 non touchscreen. The symptoms are that: Repairing or reinstalling windows freezes no matter how i try it. Live Ubuntu that works on any other computer also freezes while trying to load it. The RAM sticks and the harddrive work fine in other computers. I broke off the connector by accident, CN4750 and was using the laptop for a while with no coin battery. According to this schematic I found on here, which I THINK is the correct schematic, pins 2, 3, and 4 should short to ground, and they do. However since the pad is totally torn off from pin 1, which would be the positive terminal of the coin battery, aka P3V3AL_RTC_BAT, I'm not sure where to solder a new connection to. Here's the strange part: with the laptop battery(not coin battery), I read ~0.3V to ground on the little pad next to the broken pad that looks like maybe a test point. With the laptop battery out and the AC Power in, it reads 0.4V, however all other 3.3V circuits read as normal, the laptop starts into the bios, fine, passes MemTest, etc. I have attached pics of the area in question and of the circuit from the schematic.

[m1ch43lzm]

Hi, it's visible if you zoom in the picture you posted

Here, I marked it with a yellow line


Schematics: https://www.badcaps.net/forum/troubl...0-g1-schematic
No boardview available unfortunately

The other end of the resistor goes to D4750, it may be located on the other side of the board

Measure the voltage at pin 3 of D4750, you should get close to 3v with the RTC battery connected and no power to the board, after you fix the trace



3v should also be also present at pin 3 of the diode when the board is connected to power even if the RTC battery is disconnected

[nerdmafia]

Hi, it's visible if you zoom in the picture you posted

Here, I marked it with a yellow line

Thank you very much for taking the time to respond and provide lines/files! Maybe I'm just being paranoid, but are you 100% sure that everything in your yellow line should be one trace? And why am I reading 0.4 V at that undamaged part of the trace, that I previously assumed was a test point?

Schematics: https://www.badcaps.net/forum/troubl...0-g1-schematic
No boardview available unfortunately

The other end of the resistor goes to D4750, it may be located on the other side of the board

Measure the voltage at pin 3 of D4750, you should get close to 3v with the RTC battery connected and no power to the board, after you fix the trace

Thank you for this! I definitely plan to once more disassemble the board and find D4750. But sorry for the noob question: This is my personal laptop not a customers. The BIOS settings seem to always persist even with the coin battery now missing. Sometimes if i REALLY try to clear all residual electricity, e.g. disconnected all power, hold down the on button for 60 seconds, and even short pin 1 of CN4750 to ground, the date and time will revert back to the date of the most recent BIOS update. I'm about to know with certainty whether my issues(can't install OS, can't boot live OS) have anything to do with this coin battery issue, but it's looking like it's not related. I was able to boot into Ubuntu 24 from a USB 2.0 thumbdrive and everything was working fabulously.

Question: Do I really need the coin battery?

Also thank you that was the schematic I was using, thanks for confirming.

3v should also be also present at pin 3 of the diode when the board is connected to power even if the RTC battery is disconnected

[m1ch43lzm]

Thank you very much for taking the time to respond and provide lines/files! Maybe I'm just being paranoid, but are you 100% sure that everything in your yellow line should be one trace? And why am I reading 0.4 V at that undamaged part of the trace, that I previously assumed was a test point?

99% looks like it is, the test point is part of the trace
The 0.4v you get at the test point may be that D4750 is faulty/leaky, or your multimeter is picking up noise

Check the voltage at P3V3_RTC (after D4750), should be around 3v
With all power unplugged measure D4750 according to the drawing above, multimeter on diode mode

red probe on pin 1, black probe on pin 3
red probe on pin 2, black probe on pin 3

Black probe on pin 1, red probe on pin 3
Black probe on pin 2, red probe on pin 3

The BIOS settings seem to always persist even with the coin battery now missing. Sometimes if i REALLY try to clear all residual electricity, e.g. disconnected all power

That circuit is powered either from the always on +3.3v, or the RTC battery, that's what the diode does
So if you keep the main battery installed it won't lose the BIOS settings and date/time, of course it will reset the BIOS settings when you remove the main battery

I'm about to know with certainty whether my issues(can't install OS, can't boot live OS) have anything to do with this coin battery issue, but it's looking like it's not related. I was able to boot into Ubuntu 24 from a USB 2.0 thumbdrive and everything was working fabulously.

Maybe a BIOS reset was needed after all, when you removed the main battery and AC adapter (and missing RTC battery/coin cell)

Question: Do I really need the coin battery?

Only if you remove the main battery, or when it gets fully discharged

[nerdmafia]

thank you for the detailed response! I will disassemble and post readings. I was very careful and triple checked the 0.3v - 0.4v, both with just battery and just power, maybe when I broke the coin battery 2-pin connector I scratched the pcb and caused a small bridge. Will update shortly.