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Ohming Out Laser Printer Fusers- Top 4 Causes of 50 SERVICE and 920-925 Error Codes

Updated: Jun 13, 2019

One of the most common errors in laser printers, next to paper jams, is the fuser temperature error. Depending on which brand of printer you are working with, problems with fuser temperature will yield one of the following errors:

Most HP and Canon printers - “50 SERVICE” Most Lexmark printers - 920-925 error codes


Ohming Out Laser Printer Fusers Troubleshooting 50 SERVICE 920-925 error codes

Why the Error Occurs

These errors occur when the upper fuser roller is unable to reach or maintain a fairly narrow temperature range—hot enough to fuse toner to paper, but not so hot as to scorch the paper. To achieve a temperature in this range, the printer monitors fuser temperature and applies power to the fuser’s heating element as needed.


What Causes the Error

You can usually find the cause of the error in the following places:

  1. Printer Fuser - This is the most common cause, usually due to a burned-out heating element or halogen lamp.

  2. Laser Printer control circuit (DC controller or engine board)

  3. Laser Printer Power supply

  4. Faulty connections between any two of the above.


How to Test the Fuser

Fortunately, most bad fusers can be detected by measuring the heating element (or lamp) and the thermistor—the temperature-sensing element—with an ohmmeter. In this article and in next month’s issue, we will show you the most popular fusers, where to take the measurements, and what kind of readings to expect. If your readings are outside the ranges you will see, it is likely that your fuser is bad. Some general tips:


1. For safety and for accurate measurements, the printer must be powered off and the fuser removed from the printer before taking measurements. While you have the fuser out of the printer, also inspect its rollers, gears, etc. for wear. If these parts are worn, it’s a good idea to replace the fuser even if it’s not causing the error. If the pickup rollers, transfer roller, etc. are also worn, you can purchase maintenance kits that include some of these parts, as well as the fuser.


2. The fuser should be at room temperature for accurate measurements. If the unit is at a lower or higher temperature, the thermistor reading may differ from the values given below. If measuring a hot fuser, give it time to cool off before taking measurements.


3. Most fusers are available in several versions to accommodate different line voltages (110V, 220V, and in some cases, 100V for Japan). Thermistor readings should be in the same range for all versions of a given fuser, but the resistance of the heating element or lamp will vary with the rated line voltage. Values given below are for the 110/115V versions. A 220V fuser should have a resistance reading about four times the given value; a 100V fuser will read about three-fourths of the given value.


Many printers have timing circuits to allow the printer time to recover after a fuser temperature error, which is a necessary safety feature if the error involved overheating. For this reason, whenever you get this error, the printer should be left turned off for at least fifteen minutes before attempting to power it up again. Otherwise, you will still get the error, even though you may have fixed the original problem.


Other Helpful Resources

Metrofuser is a leading global innovator, manufacturer of printer parts, equipment, diagnostics, repair information and systems solutions for professional users performing critical tasks. Products and services include hp printer parts, printers and printer repair training. Parts include hp printer parts such as printer fusers, printer maintenance kits and other hp printer replacement parts. The company's, customers include office equipment dealerships, online retailers, repair centers and MPS service providers nationwide. Metrofuser has been named to Inc. Magazine’s fastest growing companies five consecutive years. Contact us at 908-245-2100, Dial 0 for sales




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