Pro 7900 and 9900 Field Repair Guide 10/6/10
Random Nozzle Firing Printer Component, Software Item, LCD Display, Printer Button Page 240.
Random Nozzle Firing
Note: Random Nozzles refers to Nozzles that fire when they are not commanded to.
Random Nozzle firing is caused by 1 or more of 6 components
•Head Cables
•Print Head
•Main Board
•Power Supply
•Carriage Encoder and Encoder Strip
Head Cable
Inspect the Head Cables for worn insulation. The data is sent to the Print Head by a Serial Data Bus. There is 1
data path for each color. A 0 volt potential on the Data Bus equals data. A 5 volt potential on the Data Bus equals no
data. A short to ground on the data path causes all Nozzles on the shorted Bus to fire, as long as the short is in
place. Insulate the worn Cable with tape, or replace the Cable.
Print Head or Main Board
If the random Nozzle firing is caused by serial communication problems between the Main Board and the Print
Head, the frequency of the random Nozzle firing changes when the printing resolution is changed. If changing the
printing resolution affects the random Nozzle firing, change the Main Board and the Print Head. Change them one
at a time in any order. Test between each change.
Power Supply
Sometimes (very rare) a noisy Power Supply causes random Nozzle firing.
Encoder and Encoder Strip
There is some evidence that random nozzle firing (especially yellow nozzles) can be triggered by a dirty Carriage
Encoder Strip or a Carriage Encoder that is not properly aligned to the Encoder Strip.
To Next Page
Loading...
