NAS won't start or keeps blinking? Here's how to check if the power supply is faulty
In short: a blinking light doesn't automatically mean a faulty power supply. On Synology the power LED blinks during a perfectly normal boot, on WD My Cloud it often means a file system check is running. A power supply is suspect when no light comes on at all, the power LED blinks for more than 20 minutes, or the device shuts down as soon as it's under load – think of the drives spinning up or the fan starting.
1. What's normal and what points to a power supply problem?
| Brand | Normal | Points to the power supply |
|---|---|---|
| Synology | Power LED blinks while booting | Power LED blinks for more than 20 minutes, or the light on the adapter blinks/stays off |
| QNAP | – | No light comes on at all |
| WD My Cloud | LED blinks white/blue or is solid amber: file system check running – don't switch it off | No light comes on at all |
| FRITZ!Box | – | No light comes on at all |
If the STATUS LED on a Synology is orange, Synology itself says it's more likely the fan, temperature or drives, not the power supply right away.
2. Test in 3 steps
- Rule out power and accessories. Use another outlet where other devices work. Unplug for 5 seconds and plug back in, disconnect USB devices and expansion cards (think of an external hard drive or a USB stick in your NAS).
- Look at the power adapter itself. Many adapters have their own light. If it blinks or stays off, the adapter is probably faulty.
- Measure, then swap. Technically minded? Measure the output voltage at the plug with a multimeter (black on minus, red on plus) and compare it with the label. Note: a multimeter measures without load. An adapter can measure correctly without load but fail to deliver power once a load is connected.
3. Which replacement power supply fits?
- Voltage (V): exactly the same, e.g. 12 V.
- Current (A): equal or higher is fine, the device only uses what it needs. Never take a lower value.
- Plug: barrel plugs with 5.5 mm outside have 2.1 or 2.5 mm inside. A 2.5 mm plug fits a 2.1 mm jack mechanically, but gives a loose contact at best.
- Polarity: the symbol on the label shows whether the inner pin is positive. Wrong polarity can damage the device. Most common is the inner pin positive, but reversed models exist too.
- 4-pin exception: the larger Synology / QNAP devices (e.g. DS918+, DS920+, DS923+) don't use a barrel plug but a 4-pin DIN plug (12 V, 8.33 A, 100 W). Watch out, there are devices that need 100 watts and devices that use 120 watts.
- Watts? Watts are voltage x current. If your device needs e.g. 12 volts and 5 amps, your power supply needs to be 60 watts. Always use the voltage on the device side. This has nothing to do with the voltage at the wall outlet (EU/UK 230 volts – US 120 volts).
Ratings per device: Synology · QNAP · WD · AVM FRITZ!Box · TP-Link · Ubiquiti
Data gone rather than a broken power supply?
If the NAS starts with a working power supply but your volumes are gone or your files are damaged, no power supply will help. Don't experiment any further and ask a data recovery specialist.