• 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.
CPU Printed Circuit Board
The CPU printed circuit board contains seven chips that provide the
'brains' of the system, see Figure 5-14. Each of the chips is
explained brieflyr to enable selecting the correct chip to replace.
If the selection of a chip does not correct the problem, then replace
the chips in the order that they are presented.
Figure 5-14. CPU Printed Circuit Board, Locations
• A303 - This is the 6502B Microprocessing Unit.
• A301 - This is the CTIA chip, which is used to generate all video
and sync signals for the television screen. The PORT Test indicates
a defective CTIA chip by displaying a '1' in Row F, any position.
• A302 - This is the ANTIC chip, which is used for both control of
the CTIA and refresh operations on the dynamic RAM memory.
• Z303, Z304 - These are 74LS244 chips used as one direction tri-
state buffer for MPU address lines.
• Z302 - This is a 7474 chip used to generate phase 1 and 2 clocks as
well as processing HALT commands.
• Z301 - This is a 74LS02 chip used to help in the generation of the
phase 1 and 2 clocks, helps with the processing of HALT commands
and Read/Write signals.
• 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.
ATARI Personal Computers 5-26
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