Unisys E-@CTION EFP9800 - Manual (Page 18)

About the EFP9800 Printer
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Note: A Running Change acoustic noise reduction enhancement was
released for the EFP9840 and EFP9841 serial interface units. This
Running Change incorporates a new solenoid clamp assembly and a
revised controller PCBA to further reduce acoustical noise. The
change was incorporated into factory production starting at serial
number 5108 67054. All EFP9840 and EFP9841 units with serial
numbers 5108 67054 and above will have the acoustic enhancements.
The new solenoid assembly has a bumper added to the plunger to
reduce noise. This new solenoid requires a new lower case and
therefore cannot be installed in The EFP9840 and EFP9841 units
below serial number 5108 67054.
The revised PCBA incorporates a modified print head pin firing
scheme. The PCBA fires the pins in staggered pairs to reduce
acoustical noise. This new PCBA is fully backward compatible with
previous style EFP9800’s.