How do I fix white vertical bars or blank labels?

Check Your Label Material

If you're printing with a direct thermal label, you must use direct thermal compatible labels. Direct thermal labels are coated with an invisible ink that turns black when heated. You can not use "Thermal Transfer" (TT) labels in a "Direct Thermal" (DT) printer. However, you can use DT labels in a TT printer.

The Blank Label

Every once in a while a label will find its way stuck to something it shouldn't be. It could be your shoe, the floor, a cat or the inside of your printer.

When a label gets stuck inside the printer it can "clog" the print head. The print head is the hot part of the label printer, and if it's covered it will not transfer enough heat to "print" your labels.

Here's an example of a blank label. Quite ordinary... except, it should have something printed on it. What's going on?

The Test Label

It's sometimes handy to print a test label that will have better luck showing a pattern across the label. It can be anything, but try to exercise the full print width of the label with some kind of pattern that let's you locate the issue. Here we use circles across the 4" width of the printer.

Here are the results...

Oh... very interesting! It's just part of the print that's missing. This tells us that something is blocking the print head from heating this area of the label.

The Print Head

Open the printer and check the print head. Here's a mydpi 300v1 print head at the top of the image:

That blue tape is definitely not supposed to be there.

Here's a more detailed photo showing the problem area.

Clean the Print Head

The solution is to remove the plastic tape, taking care to not scuff the print head underneath.

Find yourself some rubbing alcohol and clean the print head every few weeks. This will keep your thermal printer happy.