PC keyboard troubleshooting at the hardware level A desktop PC shows intermittent keyboard lockups even after replacing the keyboard with a new unit. Which of the following is the LEAST likely root cause?

Introduction / Context:
When a PC keyboard freezes intermittently, technicians must decide whether the fault lies with the peripheral or with internal system hardware. This question evaluates structured troubleshooting, probability reasoning, and knowledge of the keyboard signal path from the device to the motherboard controller.

Given Data / Assumptions:

• The old keyboard was swapped for a known-good replacement.
• The symptom (intermittent lockup) persists with the new keyboard.
• No mention of liquid spills or obvious mechanical damage on the new unit.
• Standard desktop PC with PS/2 or USB interface.

Concept / Approach:

Root-cause analysis weighs likelihoods. If replacing the peripheral does not change the symptom, the failure is typically upstream: port connector, cabling, keyboard controller (on older systems the Super I/O), or wider motherboard issues such as power rails or ESD damage. The chance of two unrelated keyboards being bad in the same way at the same time is small compared to a persistent system-side fault.

Step-by-Step Solution:

Verification / Alternative check:

Test the same keyboard on another PC; test a known-good spare on the suspect PC; try a USB-to-PS/2 adapter or alternate port; check system logs for controller resets; run diagnostics from firmware or the OS. If problems follow the PC, not the keyboard, the system hardware is implicated.

Why Other Options Are Wrong:

Keyboard controller chip: common failure point causing intermittent lock or missed scans. Connector: bent pins or cracked joints frequently cause intermittent contact. Motherboard: power or ground issues can disrupt the entire input path. “None of the above” is incorrect because the least likely option truly is a second bad keyboard.

Common Pitfalls:

Assuming “new equals good” without testing on another system; overlooking port damage; forgetting firmware/BIOS settings that may disable legacy PS/2; ignoring ESD history.

Final Answer:

A second bad keyboard.