• Before a chip is changed or a board is added to or removed from the
system, power the system down.
5.4.5 Motherboards
The 400 and 800 Motherboards contains several integrated circuits
with many diverse functions. Each of the integrated circuits is
explained briefly, to let you choose the correct chip to replace. If
the replacement of a chip does not correct the problem, then replace
the chips in the order that they are presented. Refer to Figures 5-15
and 5-16.
400 Motherboard
• A101 - Used to control POT lines, audio signal, keyboard
information lines as well as printer and floppy control lines
(POKEY chip).
The PORT Test indicates a defective POKEY chip by displaying a '1'
in Rows G, H, I, or J in any position.
• A102 - Used to control joystick lines, and Program Cassette
Recorder control lines (PIA chip).The PORT Test indicates a PIA
chip by displaying a '1' in Rows A, B, C, D, or E in any position.
• Z102 - Used to receive data from POKEY chip, translate the
information and send it to the keyboard.
• Z101 - Used to receive data from the keyboard, translate the
information, and send it to the POKEY chip.
• Z104 - Used to decode RASTIME and R/'4V Late signals.A111 - Used as
buffers for video and lum lines. Also part of the Power ON Reset
Circuit.
• Z103, Z015 - Used to decode Memory Map for computer.
• A103, A104, A105 - Used to hold Operating System and some BASIC
Language programs.Use only known good chips and leave substituted
chips in the printed circuit board until the failing chip is
identified.
• Test printed circuit board in system after each chip is replaced to
determine if failure continues.
• Before a chip is changed or a board is added or removed to/from the
system, power the system down.
5-27 System Service Manual
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