Atari 800XL Service Manual

SECTION
4
TROUBLESHOOTING
The
Troubleshooting
Guide
is
designed
to
aid
in
arriving
at
rapid
diagnosis
of
the
following
problems,
listed
in
the
most
common
order
of
failure.
Each
symptom
is
accompanied
by
some
possible
causes,
aid
suggested
solutions.
Instructions
for
disassembly/assembly
are in
SECTION
3 of
this
manual.
SYMPTOM
POSSIBLE CAUSES
SOLUTION
Snowy
Screen
TY
Switch
Box,
ON/OFF
switch,
Channel
Select
switch,
RF
Modulator
Adjust
or
replace
Defective
Power
Supply,
Damaged
RF
Cable
Replace
Defective
(open)
components
on
+5Cline.
Isolate
and
replace
Defective
(shorted)
components
on
+5A,
B
and/or
C lines.
Isolate
aid
replace
Defective
(shorted)
LSI's
and/or
ICs
Isolate
and
repair
No
Color
or Bad
Color
RF
Modulator
or R38
Adjust
or
replace
U17,
U20.Q1
,Q3,CR2,CR3
Troubleshoot
color
/video
circuitry;
replace
defective
1
C/component.
Y1
Yerify
3.579545
MHzfreq.
of
Y
1 ;
replace
if
defective.
27

Atari 800XL Specifications

General

Manufacturer	Atari
Type	Home computer
Release year	1983
CPU	MOS Technology 6502C
RAM	64 KB
ROM	24 KB
Operating System	Atari OS
CPU Speed	1.79 MHz (NTSC) / 1.77 MHz (PAL)
Graphics	ANTIC and GTIA chips
Display resolution	160×192 to 320×192 pixels
Sound	POKEY chip
Storage	Cassette tape, floppy disk
Ports	Serial, parallel, monitor, joystick ports