Printronix 108525-001, Maintenance Manual

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2-44 P6040/P6080 Principles of Operation
2-8. Hammer Bank and Shuttle Mechanics/MPU
a. Hammer Bank Assembly/Shuttle
Operation of the hammer bank is as described in paragraphs 2-3b and c.
b. Magnetic Pickup (MPU) (Figures 2-18 and 2-19).
Printing is synchronized with shuttle movement by the magnetic pickup (MPU) signal. The magĆ
netic pickup, located next to the flywheel timing disk, is so oriented that timing signals relate preĆ
cisely to the shuttle position. Variations in magnetic reluctance are sensed by the magnetic pickup
from apertures (198 for P6040; 138 for P6080) on the timing disk as it rotates, generating SYNC
pulses. Two aperture locations at opposite ends of the disk are of double width (material between
two adjacent apertures is removed). These double width apertures separate the 138 single width
apertures into two groups and generate a RESYNC signal each time the shuttle begins moving to
the right.
Full rotation of the disk provides four printing periods and two back and forth shuttle cycles. Each
printing period is followed by a turnaround period when the shuttle movement is reversed, paper is
advanced 0.0139 inches, and no printing occurs. During each of the four printing periods each
hammer covers an area three characters wide for P6040 and two characters wide for P6080. An
entire dot row is printed in 36 SYNC periods for P6040 and in 24 SYNC periods for P6080.
The SYNC pulses are distributed to other printer logic including missing pulse" detection logic
that generates the RESYNC pulse.
The SYNC signal performs the following functions:
- Initiates a high speed scan of all 132 print buffer locations during which each character is
presented to the character generation logic.
- Activates all hammers armed with a logic 1" during the previous scan of the printer
buffer.
- Initiates a time out period which controls generation of the hammer reset signal (NHRS).
This signal resets hammer driver circuits previously activated by SYNC for the prior dot
location.
In the generation of SYNC and RESYNC signals, the roughly sinusoidal output of the magnetic
pickup is amplified and converted to a TTL compatible square pulse by a circuit on the power supĆ
ply PCBA. The resulting MPU signal is synchronized with the printer clock (CLK) and applied to
print synchronizing circuits on the logic C3 PCBA.
Typical signal levels received from the magnetic pickup are:
SYNC: 2.0 to 3.5 Vpp
RESYNC: 4 to 6 Vpp
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