Printronix p300 Maintenance Manual page 54

2–5. Print State
–continued
j. Print Mechanism
–continued
As the shuttle is driven to the left, the other cam lobe drives the counterweight to the right against the coun-
terweight spring. This spring then returns the counterweight to the left as the other low point of the revolv-
ing cam turns toward the counterweight. This symmetrical arrangement reduces vibration by balancing
the horizontal reaction forces of the shuttle.
The P300 print mechanism has 44 evenly spaced print hammers fixed to its hammer bank. The hammer
bank travels horizontally 3/8 inch while printing. In data processing print mode (300 LPI), each hammer
prints the entire dot pattern of three adjacent character columns.
The P600 print mechanism has 66 print hammers fixed to its hammer bank. The hammer bank travels hori-
zontally 1/4 inch while printing. The P600 may be configured for either of two printing methods: phased
fire and non–phased fire. Early P600s were non–phased fire exclusively and can be identified by a lack of
heat sinks on the hammer coils. More recent P600s can be configured to print using either method. Non–
phased fire printers have their hammers evenly spaced. Phased fire version hammers are not evenly
spaced.
The most recent P600s (S/N C31579 and subsequent) are configured at the factory for phased fire opera-
tion. They may be modified for non–phased fire operation. Non–phased fire units may be modified in the
field.
The phased fire configuration permits continuous heavy duty operation without overheating, reduction in
speed, or loss of print quality. A phased fire P600 has a unique hammer alignment. The hammers are paired
and tilted toward each other 1/2 dot column. (See Figure 2–21.)The phased fire P600 also has a phased fire
A4 (P/N 105777), A6, or A7 logic PCBA with jumper W1 installed. Pre–phased fire A4 PCBAs (P/N
103831) did not have this capability and should be used only for standard P600 (or P300) installations.
Timing of the phased fire logic reduces peak instantaneous current demand in the coils which reduces hys-
teresis losses and heat dissipation. In operation, the phased fire P600 tends to fire the hammers alternately.
In fact, this occurs consistently only when identical characters are being printed. For identical characters,
the odd hammer prints while the even hammer is idle. After the shuttle moves one dot row (the cumulative
offset of the even hammer), the even hammer prints its dot in the corresponding column of its character
field while the odd hammer recovers from its previous strike.
2–32 P300/P600 Principles of Operation