This problem shows up as missing dots on the page followed by a blob of ink. This situation only occurs with the the color printhead. The problem rarely occurs, because it requires three conditions:
1) Printing very heavy density color area fills across the whole page.
2) Printing at engine speed (meaning that the printer can't be pausing
during printing).
3) Printing in Normal mode (not an option for transparencies, where
colored backgrounds are often used).
Even when these conditions are met, the problem occurs on only 1.5% of pages printed.
The fix is to switch the printing mode to BEST.
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