Printer won’t power on — adapter, fuse, and PSU test checklist

Joe B.

Reviewed for technical accuracy

Specialities: Power supplies (PSU/SMPS), Printers, Hardware diagnostics, Windows & macOS

Printer has no power — how to test adapter, fuse, and internal power supply (PSU)

Technician

Hi! Let’s revive a printer that won’t power on. We’ll start with outlet checks and a hard power reset, then move to a power adapter voltage test, fuse continuity test, and an internal PSU inspection. We’ll watch for symptoms like no power light, faint clicking, or powers then dies. This guide covers popular brands — HP, Epson, Brother, Canon — and both inkjet and laser printers.

Customer

My HP DeskJet is completely dead — no LEDs, no display. The printer won’t turn on even after unplugging and plugging back in.

Technician

Rule out simple power issues first:
• Plug the printer directly into a known‑good wall outlet — avoid power strips and UPS for testing. Verify the outlet with a lamp/phone charger and check the GFCI/breaker.
• If you have an external brick (e.g., 32V/12V HP power adapter or 24V Epson/Brother adapter), note whether its LED turns on.
• Do a power reset: unplug power and all cables, press and hold the power button for 30–60 seconds to discharge capacitors, wait 1 minute, then reconnect.

Customer

Tried two outlets and a different cord. Still no power. The adapter has no light.

Technician

Test the power adapter (SMPS) with a multimeter:
1) Read the label — common ratings are 32V/12V (HP) or 24V (Epson/Brother/Canon) DC; center pin usually positive (+).
2) Set the multimeter to DC V. Probe the barrel connector — red to inner pin, black to outer sleeve. Expect within ±10% of rated voltage under no load.
3) If you read 0V, pulsing, or very low voltage, the power adapter is faulty. Replace it with an exact‑spec OEM brick. Underrated third‑party adapters cause no power, random shut‑off, or clicking.

Customer

If the adapter checks out, what else prevents a printer from turning on?

Technician

Check the fuse and internal power supply (PSU):
• Many models include a user‑serviceable AC input fuse or a board‑mounted thermal fuse. With power unplugged, do a continuity test; continuity = good, open = blown fuse.
• Inspect the PSU board for bulged capacitors, burn marks, or a short on the DC rails. A shorted carriage motor/fuser/scan lamp can trigger over‑current so the printer won’t power on or instantly powers off.
• If your printer uses a detachable PSU module, try a swap with a known‑good module.

Customer

I don’t own a multimeter. Any way to test without tools?

Technician

No‑meter methods:
• Borrow or swap a matching OEM adapter (same voltage/connector/polarity).
• Bypass surge protectors: plug directly into a different wall outlet/circuit; reset any tripped GFCI.
• Disconnect USB/Ethernet and remove cartridges; a shorted accessory can keep the printer from turning on.
• Listen/feel for a faint click from the adapter on plug‑in; repetitive clicking suggests over‑current protection due to a downstream short.

Customer

If the fuse is blown, is it safe to replace it myself?

Technician

Safety first: Unplug the printer and wait 5–10 minutes for capacitors to discharge. Replace only with the exact fuse rating (T‑slow/fast, amps, volts). Never bypass a fuse. If a new fuse blows immediately, the PSU or main board likely has a short — stop and seek service to avoid further damage.

Customer

My Brother laser has no external brick — where do I look inside?

Technician

Internal PSU checklist (laser & some inkjet):
• Verify low‑voltage outputs (usually 5V/12V/24V). Missing rail ⇒ failed regulator or primary switch transistor.
• Disconnect loads one by one (formatter/main board, scanner, Wi‑Fi board, fuser) to isolate a short circuit that keeps the PSU in protect mode.
• A failed thermal fuse in the fuser or a shorted heater can cause instant shut‑down when you press power.

Customer

What’s the quickest path to get it to power on today?

Technician

Quick path to restore power: wall outlet test → hard reset → swap/measure adapter → check/replace fuse → inspect the PSU board and disconnect loads to find a short. Need help confirming adapter specs or fuse type? Open the chat and I’ll walk you through live.

Customer

If it starts but then shuts off during warm‑up, what should I check?

Technician

Powers on then off: That points to a weak adapter or failing PSU under load. Laser printers draw high current at warm‑up (fuser). Try another known‑good OEM adapter (if external). For internal PSUs, inspect the fuser and DC controller; a short on the 24V rail can trigger power cycling.

Customer

Great — can you summarize the steps so I don’t miss anything?

Technician

Summary: To fix a printer won’t power on issue — verify outlet & breaker → do a hard reset → test or swap the power adapter → check/replace fuse → inspect PSU board and isolate shorts → print a test page. If you want live help, open the chat; I’ll tailor steps to your exact model.

Quick answer: the accepted fix

Accepted fix when a printer won’t power on: test a known‑good outlet and perform a hard reset, then measure or swap the power adapter. If voltage is bad, replace the adapter. If the adapter is good, check the fuse and inspect the PSU board for shorts on the DC rails. These steps restore power in most HP, Epson, Brother, and Canon models.

FAQ

Step-by-step (adapter, fuse, PSU)

1. Plug into a different wall outlet; reset any GFCI/breaker. Avoid power strips for testing.
2. Perform a hard power reset (unplug, hold power 30–60s, reconnect after 1 minute).
3. Test or swap the power adapter (expect 32V/12V HP or 24V Epson/Brother/Canon). Replace if out of spec.
4. With power unplugged, do a fuse continuity test and replace with the exact rating if blown.
5. Inspect the PSU board for damage; disconnect loads to find shorts; confirm stable 5V/12V/24V rails.

Sources

• SMPS basics
• HP Support — Power and Adapter specs
• Brother Support — Power/Thermal fuse info

Matt ● replies in < 1 min

Technician Expert

⭐⭐⭐⭐⭐ Trusted by 27,000+ customers

Alex · Expert's Assistant

Start Chat

5 Tech Support Specialists are online right now.