A technician is troubleshooting a computer that unexpectedly shuts down during operation and refuses to turn back on until the AC power cord is unplugged for several seconds. Place the diagnostic steps in the correct order to determine if a tripped power supply unit (PSU) protection circuit or a motherboard short is causing the failure.
- 1Unplug the AC power cable from the wall outlet and wait 30 seconds to drain residual flea power.
- 2Disconnect all internal power cable harnesses (24-pin ATX, 4/8-pin EPS, PCIe, and SATA) from the motherboard and internal components.
- 3Bridge the PS_ON pin to a ground pin on the 24-pin ATX connector using a paperclip or PSU jumper tool, then reconnect main AC power.
- 4Measure DC voltage output on the +3.3V, +5V, and +12V rails using a multimeter.
Answer
The correct diagnostic sequence is: 1) Unplug the AC power cable and wait 30 seconds to drain flea power, 2) Disconnect all internal power cable harnesses from the motherboard and components, 3) Bridge the PS_ON pin to ground on the 24-pin connector and reconnect AC power, and 4) Measure DC voltage output on the +3.3V, +5V, and +12V rails using a multimeter.
When a system shuts down and requires AC power removal to turn back on, a PSU safety circuit has tripped. The proper order of operations requires first clearing flea power by disconnecting AC power. Next, all internal hardware components must be disconnected to isolate the PSU. Then, bridging the PS_ON pin manually tests basic power-on capability. Finally, using a multimeter verifies that output voltage rails fall within standard ATX specifications.
Step-by-Step Solution
Key Concept
Power Supply Unit (PSU) Protection Circuit Reset and Isolation Testing