Circuit Board Description - Oki ML390 Service Manual

Page: 17
Service Guide ML390/391
Chapter 2 Principles of Operation

2.2 CIRCUIT BOARD DESCRIPTION

2.2.01 Operator Panel Board
The operator panel board contains switches and LEDs which allow the end user to control and monitor the
printers operation. For specific information on the capabilities and use of the operator panel, please refer
to Operation in the Setup Guides or Chapter 1: Front Panel Control in the Reference Guides.
2.2.02 Power Supply
The power supply consists of a power transformer, filter board and a DC power supply board. The AC
input voltage is stepped down to 8.6 VAC, 46 VAC and 10 VAC by the power transformer. These AC
voltages are converted into + 5 vdc, + 8 vdc, and + 40 vdc by the power supply board for use throughout
the printer.
Power Transformer
If the transformer temperature rises above a pre-determined level, the built-in temperature fuse opens to
prevent damage to components in the printer. Once this fuse opens, the transformer MUST be replaced.
Filter Board
The power switch, line fuse, and line filter are mounted on the filter board.
Power Supply Board
This board transforms AC voltages into + 5 vdc, + 8 vdc and + 40 vdc for use throughout the printer.
2.2.03 Control Board
Microprocessor
The microprocessor is the nucleus of the control circuitry. All peripheral circuits operate under the control
of the microprocessor.
For the Rev A, B, and C printers, the microprocessor is Q8 - 80C154.
Program Read Only Memory (ROM)
The printers control program is stored in the Program ROM. The microprocessor operates under the
control of this program.
For the Rev A, B, and C printers, the Program ROM is Q12 - 128 kilobytes.
Random Access Memory (RAM )
The RAM stores the following information.
· Data to be printed (Receive Buffer)
· All character fonts
Q1 and Q2 provide 64 kbytes of RAM. The battery backup retains data when power is removed.
Character Generator Read Only Memory (CGROM)
This stores the resident character fonts.