HP Laser Printer technicians that utilize Halfway Print Tests live longer, happier lives.
Many types of HP printer errors and problems have multiple possible causes, so it’s
not always easy to determine which part you need to fix a given problem. Some
troubleshooting is often necessary to narrow down the possibilities.
One of the most useful troubleshooting techniques is the “halfway test,” also called the “stop test.” It is useful whenever you have an image defect or a paper skewing or wrinkling problem, because it allows you to determine where in the paper path the problem is originating.
Here’s how it works:
send a print job or print a configuration page, then stop the page part way through the printer by opening the lid. For image problems, the ideal time to stop the paper is when about half of it is past the toner cartridge. Remember that the toner is unfused at this point, so be careful not to make a mess!
Presumably, you already know what the image defect looks like on a completed print. This test allows you to view the image in two earlier stages: on the paper before it goes through the fuser, and on the drum inside the toner cartridge, before it gets transferred to the paper.
If the image looks good in both of these places but bad on the finished print, it’s a
pretty good bet that the fuser is causing the problem. If it’s bad on the paper
before fusing but looks good on the drum, then the problem is originating in the transfer stage—bad transfer roller or high voltage to the transfer roller. If it’s already bad on the drum, you can eliminate the fuser and transfer roller and conclude that the defect is originating at an earlier stage in the print process—perhaps a bad formatter board, laser/scanner unit, or the toner cartridge itself.
For skewing or wrinkling problems, you may want to stop the paper at various
different points in the paper path to try and isolate where it first skews or wrinkles. For example, if the paper is straight whenever you stop it before the registration rollers, but skewed whenever you stop it after that, the registration assembly is a top suspect. If paper is wrinkling in the fuser, but is already skewed before that, there’s probably nothing wrong with the fuser—the paper is wrinkling because it’s feeding crooked, so the fault is earlier in the paper path.
It takes some practice to be able to stop the paper in the desired spot—one way
to make it easier is to feed from the manual tray. This allows you to watch the paper as it moves into the printer, and it will be easier to judge its position.
This is especially important on color printers with more complex print cycles, because paper movement is often delayed while the image is developed in several stages, and it’s hard to tell where the paper is at any given time if you can’t see it.
Lets Take a look at a Example
It’s early morning, you’ve just jumped into your vehicle and you haven’t had enough coffee to get you going for the day. A customer calls and states “I have a faint gray haze in the background of every page I print. Can you help me?” You had a similar problem a few days ago with another monochrome printer.
That time it was a bad toner cartridge. So you replace the customer’s toner cartridge and the same problem keeps occurring. Is it possible that you have another bad toner cartridge or is it feasible that you diagnosed the wrong problem? It’s way too early in the morning to have to stress out or spend unnecessary money on another part.
A faint gray haze could mean the following printer parts are bad: the toner cartridge, transfer roller, high-voltage power supply, DC controller or even the fuser. So how are you to know which is the culprit? The answer is the halfway test! Remember that the Image Formation process is divided into the following stages:
Conditioning (places a uniform electrical charge on the drum)
Writing (laser strikes surface of drum and creates latent image)
Developing (forms the toner image on drum)
Transferring (charge transfers the image to print media)
Fusing (heat and pressure produces a permanent image)
Cleaning (removes excess toner from the drum surface)
The halfway test can tell you a lot about what is going on in a monochrome printer. The purpose is to determine which stage is malfunctioning in the printer when there is an image defect. Follow these simple steps to quickly diagnose the problem:
Print a configuration page from the control panel information menu.
Open the top cover after the paper advances halfway through the printer (about three seconds after the main motor begins rotation). The leading edge of the paper should have advanced past the toner cartridge.
Remove the toner cartridge. Careful not to make a mess because the toner is unused at this point.
Open the toner cartridge drum shield to view the drum surface.
If a dark toner image is present on the drum’s surface, it is safe to assume that the conditioning, writing, developing and cleaning stages are all functioning properly in the Image Formation process.
At this point trouble-shoot the problem as a transfer or fuser problem. Perform the drum rotation and high voltage power supply diagnosis if there is no image present on the photosensitive drum.
It may be difficult to stop the paper in the desired spot when performing these tests. One way to make it easier is to feed the paper from the manual tray. This allows you to watch the paper as it moves into the printer and will be easier to judge the position.
A short and to-the-point solution. If you would like more information on common problems in monochrome printers ask your sales rep for our upcoming printer repair training classes
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