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The 79 service error HP laserjet pro 400 is nothing but a Malformed PostScript document that generates this error on HP printers. It's a regular problem with HP printers. If you see this error on your printer’s LCD. To rectify this error perform these steps –

1. On the bottom of the printer, look for the on/off switch.
2. Count to ten while flipping the switch to the off position.
3. Restart the printer, and you should be good to go.
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