Printer Faults - Constant Busy Light

Laser printers are generally in line with their specification in terms of print speed. Inkjet printer specifications tend to headline a specification that isn't normally achieved in practice. It isn't unknown for a laser printer to be a bit slower than its specification but a serious shortfall generally means there is some mismatch between what the user is trying to do and the expectations for that printer - for instance, trying to print 1200dpi pictures on a ten year old printer.

  • High Resolution - some printers (older ones) slow down to half-speed when printing at high resolution. The main reason is usually limited processing power.
  • Printers are also slower when printing some media like transparencies (they print cool but slowly) and heavy Media (they print hot and slowly)
  • Page complexity - a page of mono print can vary from a megabyte to 126 megabytes. If the printer runs out of memory it may say so - or it may just take an age to do a job.

High resolution makes extra demands in several ways. The amount of data transmitted and held in memory quadruples if the resolution doubles - so an A4 page potentially contains:

  • 7,920,000 pixels at 300 dpi
  • 31,680,000 pixels at 600 dpi
  • 126,720,000 pixels at 1200 dpi

Pages vary a great deal in their complexity as a print job and how long they will take to print. Pages scanned as PDF's by multifunction printers can prove to be rather large when printed; they get "bitmapped" meaning a page with a couple of pictures can be several megabytes in size. Look at the file size to see why a file might be difficult to print.

A printer normally won't need anything like 126 megabits for an A4 page at 1200 dpi. The page image generated is held in compressed form in memory. Compression makes the point where memory will actually run out less predictable and that might be one reason why some printers are bad at reporting that a page is too complex.

Laser printers differ from inkjets in that once the mechanism is in motion the printer can't stop it until the page has printed. A printer will ordinarily have a complete page ready in memory before the printer motors start to turn.

If the busy light stays lit for an extraordinary amount of time the page is too complicated. Usually this means that the printer runs low on memory but keeps on trying to assemble the page. The cure is either:

  • Increase the memory - unfortunately:

  • Not every printer has the capacity for extra memory - cheap printers are like cheap PCs in this respect.
  • If there is a memory slot it might be a SO-DIMM type. It's only quite recently that some printers have started to use standard desktop PC memory DIMMs.
  • Quite what hallucinogenic overload has persuaded designers of enormous printers that it's clever to use small and expensive memory devices is a subject for speculation - or annoyance. But if they put a memory slot in the thing at all perhaps we should be grateful.
  • Simplify the page - if you were trying to print at 1200dpi then try again at 600 dpi or 300dpi which involves far less data. Print drivers have a setting for resolution.