Computer ATX switching power supply maintenance considerations - Database & Sql Blog Articles

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1. The ATX switching power supply circuit board is densely packed with components arranged in a "stereoscopic" layout. Some of the lowest components are only 2mm high, while others can reach up to 50mm in height. The middle layers often divide the components into 4–5 levels, especially with two large heat sinks that block access to many parts, making them completely invisible for inspection or testing. Even some larger components are visible, but the test leads can't reach their pins. Testing from the back side becomes necessary, and since most components don’t have clear front positions, it’s hard to match the backside solder joints. Therefore, removing the two large heat sinks first is highly recommended to make the board more transparent and easier to repair safely.

2. Damage to the standby power supply is often severe and tends to recur during repairs. However, the PCB traces on an ATX power supply are usually very narrow, and the pads are small, making them prone to lifting after multiple re-soldering, which worsens the repair. A good solution is to create a short wire connection from a solder joint that may need frequent replacement. Components can be soldered onto this short line for testing, reducing the number of direct solder joints and improving repair efficiency.

3. ATX power supply fuses are typically rated at 4A, 5A, or 6A. These provide protection under normal output conditions, but during maintenance, when the output is low, the fuse may not blow even if there's a fault. If you power the unit without checking, hidden issues might persist or new ones could arise. To prevent this, it's best to connect a 1A fuse in series with the power input. If the 1A fuse blows, it indicates a short in the standby power supply, and you should focus on repairing that first. If it doesn’t blow, replace it with a 2A fuse and continue. If the 2A fuse blows, it suggests a problem in the main switching power supply. If it doesn’t, then the issue is likely elsewhere, but not a short-circuit. Always prioritize the main switch power supply after the standby one, and keep the 2A fuse as a safety measure during the process.

4. In no-load conditions, +12V may rise by 0.6V, while the 3.3V voltage regulated by "reverse current feedback" might drop instead of rising, possibly to 1.86V. This can lead to misdiagnosis and unnecessary repairs. To avoid such issues, it's best to use a CD drive as a load. Once connected, the voltages across all channels stabilize, and the optical drive’s LED indicator can serve as a visual check of power output. You can also listen to music through the headphones to confirm operation. Since the optical drive uses moderate power (5V/1A, 12V/1.5A), it perfectly suits the needs of maintenance without overloading the system.

Finally, ensure that the switch transistor and rectifier diode are not overheating before removing the large heat sinks. With a 2A fuse in place, the setup remains safe and manageable during the entire repair process.