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Difficulty: MediumMotherboards Form Factors and Connectors

A field technician is replacing a failed full-size ATX motherboard with a smaller Micro-ATX motherboard inside the existing desktop tower chassis. During installation, the technician mounts the new board using all pre-installed brass standoffs in the chassis. Upon powering on the system, the fans spin briefly, but the computer immediately turns off and fails to perform a Power-On Self-Test (POST). Which of the following actions should the technician take to resolve this installation issue?

  1. Remove extra chassis standoffs that do not align with the mounting screw holes of the Micro-ATX motherboard.Answer
  2. B
    Skip hardware checks and immediately perform a motherboard BIOS/UEFI firmware flash using a USB flash drive.
  3. C
    Replace the 24-pin main ATX power cable connection with a 4-pin or 8-pin EPS auxiliary power cable.
  4. D
    Move all installed system RAM modules into adjacent motherboard slots on a single memory channel.

Answer

The technician should remove any leftover chassis standoffs that do not align with the mounting holes on the smaller Micro-ATX motherboard to eliminate the electrical short circuit on the underside of the system board.
Removing unaligned chassis standoffs directly eliminates the physical contact between the metallic standoff and electrical components on the back of the Micro-ATX motherboard. Because Micro-ATX boards are shorter than ATX boards, case standoffs left in the bottom ATX position press directly against motherboard traces, creating an electrical short circuit that prevents POST.

Step-by-Step Solution

1
Identify the physical form factor difference between ATX and Micro-ATX.
ATX boards measure up to 12 x 9.6 inches with 9 mounting holes, whereas Micro-ATX boards measure up to 9.6 x 9.6 inches with up to 8 mounting holes.
When downsizing form factors in a single case, the standoff layout must be modified.
2
Analyze the reported symptom of immediate shutdown upon powering on.
The power supply detects a direct short circuit to the metallic chassis and activates over-current or short-circuit protection.
An unused metal standoff contacting exposed soldered pins or circuit traces on the back of the motherboard creates a short circuit ground path.
3
Determine the required corrective physical installation step.
Unscrew and remove all extra metallic standoffs from the computer chassis that do not line up with designated Micro-ATX mounting holes.
Ensures standoffs only contact grounded screw pads around dedicated mounting holes.

Key Concept

Motherboard Standoff Alignment and Short-Circuit Prevention
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Topics

Motherboards Form Factors and Connectors

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