Ricoh VT3500 Service Manual page 172

1 December 1993
9.4.3 Thermal Head Drive
CN403-16
Image Data
CN705-16
CN403-12
CLK
CN705-12
CN403-14
LSYNC
CN705-14
CN403-18
ENR
CN705-18
Image Processing
PCB
A thermal heating element may get too hot when there are consecutive black
pixel data in the sub-scanning direction. Conversely, a thermal heating
element may not get hot enough to plot on a master when there are
consecutive white pixel data in the sub- scanning direction.
To remedy this, each thermal element receives data twice for one plotting:
1. Data for the line previous is monitored by the thermal head temperature
checking circuit. Then, based on the datum obtained, the opposite datum
is sent to the thermal heating element. This either heats or cools the
element (as required).
2. The actual plotting data is sent to the element. This plots the pixel on the
master.
Thermal Head
Temperature
Image Pixel
Checking
Data Decoder
Circuit
Pulse Width
Decoder
Thermal Head Drive PCB
2-136
CN704-1
DATA 4
CN704-5
DATA 3
CN704-9
DATA 2
CN703-3
DATA 1
-23
CN704-4
ENR 1
CN704-8 -24
ENR 2
CN704-12
-29
ENR 3
CN703-6
-30
ENR 4
Thermal Head