I bought an HP ProDesk 600 G3 Mini that had a damaged CMOS battery holder. At startup it reports date and time errors, but I cannot enter the BIOS because none of the USB ports recognize my keyboard. Two ports provide power, but no data. I soldered two wires to reconnect the battery and measured roughly a 200 mV drop across the nearby three-pin component, but the problem remains.
The machine powers on immediately whenever AC is connected. I also installed an operating system on a spare 128 GB 2.5-inch SSD, but after getting past the CMOS date and time warnings, it reports that the system image cannot be authenticated. I would like to keep the original 256 GB NVMe drive, but I appear to be stuck: I cannot access the BIOS to change settings such as Fast Boot or Secure Boot, and I cannot boot normally either.
I have tried the rear USB ports and several troubleshooting steps. Could the keyboard itself be incompatible, or is the damaged CMOS circuitry likely preventing USB initialization?
2 Answers
The battery repair probably is not explained by a 200 mV reading alone; the important checks are correct polarity, a stable CMOS voltage, and continuity from the battery connections to the board. However, the battery itself normally should not prevent USB devices from working in firmware. The authentication message is more consistent with Secure Boot or another firmware boot setting rejecting the newly installed image. A basic keyboard, a different USB port, and possibly a USB-to-PS/2 solution are worth trying, but if no keyboard works before the operating system loads, the board may have damaged traces or firmware settings that require servicing or replacement.
Try the specific rear USB port intended for the keyboard. On these HP systems, one of the rear ports is designated for keyboard use and may initialize differently from the others. Also try a very basic wired USB keyboard rather than a newer model with multiple operating modes, hubs, or extra features. If that still produces no response, the damaged CMOS holder or surrounding motherboard traces may have caused hardware damage, and returning or replacing the unit may be more practical than continuing to troubleshoot it.
I tried the designated rear port, but I have not yet tested an older, simple keyboard. The keyboard I used supports three modes, so compatibility is still possible.