Updated: Jul 5, 2019
Troubleshooting HP Laser Printer Power Problems
Power problems account for a relatively small percentage of total service calls, and are generally quite easy to diagnose. On many machines, the repair is a 10-minute affair.
All too often in the past, however, I have incorrectly categorized customer complaints as power problems. Usually, the reason for this is that I failed to get enough information from the customer, reacting simply to their first comment. The customer may have said, "My machine's dead," and I instinctively thought "power problem." But on investigation I found that the machine power cycled properly but wasn't feeding paper.
When a customer approaches you with an observation that the machine doesn't do anything or is dead, ask exactly what the printer did. Did it make any noises? Did lights go off and on? Did it behave normally or abnormally when it was powered up? In short, make sure you really have a power problem before leaping to that conclusion because the customer says the machine is dead.
TWO PATTERNS Customers correctly presenting you with power problems generally offer diagnosis falling into two separate categories. Either:
The machine did absolutely nothing when it was powered up, or
There was some indication of life in the machine, but it didn't power-up like it was supposed to. Sounds or lights were different, and the machine either wouldn't print, or the print was unacceptable.
The first condition is symptomatic of loss of AC power, while the second is symptomatic of loss or unacceptable variance of DC power.
Nothing Happens You power up the machine and nothing happens. Absolutely nothing. No noise, no lights, no motors engaging. Nothing. The first thing to do is check line current. Don't go to the wall. First check the current at the connector that plugs into the printer.
Next, look for fuses and resets. Many machines have them in positions of immediate accessibility. If this fails to restore power, chances are excellent that you have an AC power problem. Some printers may require a new high volt power supply or low voltage power supply.
Stuff Happens, But It's Just Not Right
This is more common and indicates a malfunctioning DC or Low Voltage Power Supply. Laser printers use several different low voltages to power the various appliances and components within their systems. For instance, in the Canon SX Engine, the laser is driven by 24 VDC, while the Formatter PCA is driven by 5 VDC. In all laser printers, everything but the Fuser runs off DC power, and the voltages are critical even though the specific voltage levels may differ from one type of printer to the next.
Most machines have standard instructions for confirming the presence of the appropriate DC voltages, Often, though, it is simpler to replace the DC Power Supply and see if normal operation is restored.
Laser Printer Service Rule of Thumb
Much more detail would be required if we were going to service the Power Supplies themselves-we're not. Unfortunately, it's frequently easier to intuitively diagnose a Power Supply failure than it is to describe the symptoms and checks here.
In general, if there is not a good, logical explanation for your printer's behavior, and the behavior could be explained by inadequate, missing or intermittent power, change the Power Supply and determine whether that corrects the malfunction
Be aware that manufacturers anticipate some Power Supply problems. Consequently, virtually all Power Supplies have some sort of fuse on them. It may be a highly visible or it may be harder to find on the board.
The point is, there's always something like that there. If the fuse is not readily apparent, you can remove shielding or housings to expose the underlying board(s).
Look first for the obvious fuses. If nothing looks familiar, look for the designation. Once found, the fuse must be checked for continuity. If there is no continuity, there's a good chance that is the sole problem.
You may be a bit apprehensive about replacing the fuse, particularly if its replacement involves de-soldering and soldering on a printed circuit board. Certainly, if you have no experience in this area, it would be a bit aggressive 1o1 you to learn on a customer's machine. But it you do have the experience, dive right in.
If the fuse is an unfamiliar component, contact a parts adviser at Metrofuser. They will be able to match it with a suitable component.