Sharp UX-177 Service Manual page 27

6. Recording block
(1) General view
6-1. Driving
Via the pulse motor gear shaft, the reduction gear, and the recording
paper feed gear, rotation of the pulse motor is conveyed to the re-
cording paper feed roller to feed the recording paper.
6-2. Recording
Use of a thermal head permits easier maintenance and low operating
costs.
1) Thermal head
The thermal head consists of 1728-dot heat elements arranged in a
single row and has the resolution of 8 dots/mm. The maximum re-
cording speed is 10ms/line. The thermal head also incorporates a
1728-dot shift register latch and an output control driver circuit. Low
power consumption is achieved by dividing the head into nine seg-
ments.
2) Structure of the recording mechanism
Recording is accomplished by pressing the thermal head on the re-
cording paper against the platen roller.
The main scan (horizontal) is electronically achieved, while the sub-
scan (vertical) is achieved by moving the recording paper by the
recording platen roller.
Usually, the cause for uneven print tone is caused by misalignment of
the thermal head or uneven contact with the roller.
It can be checked in the following manner.
1) Check if the thermal head power and signal cables are properly
routed.
2) Check that the thermal head pivot moves smoothly up and down.
3) Check that the thermal head support bracket is secured without
any play.
4) Check to see that the recording platen roller has proper concen-
tricity, in the case of a print tone variation evenly repeated down
the page.
5) Replace the thermal head with a new one and check to see if the
same trouble occurs.
Fig. 8
Praten roller
Thermal head
Recording paper
3 – 3
Cutter unit
UX-177H