Atari 800XL Technical Service Data

TEST EQUIPMENT
Test Equipment listed by Manufacturer illustrates typical or equivalent equipment used by SAMS’ Engineers to obtain
measurements and is compatible with most types used by field service technicians.
TEST EQUIPMENT (COMPUTERFACTS)
Equipment Name
B & K Precision
Equipment No.
Simpson
Equipment No.
OSCILLOSCOPE
1570A,1590A,1596
454
LOGIC PROBE
DP51
LOGIC PULSER
DP101
DIGITAL VOM
2830
463,467,470,474
ANALOG VOM
277
260-7
ISOLATION TRANSFORMER
TR110,1604,1653,1655
FREQUENCY COUNTER
1803,1805
710
COLOR BAR GENERATOR
1211 A,1248,1251,1260 431
DISK DRIVE ANALYZER
FUNCTION GENERATOR
3020
420A.420D
HI-VOLTAGE PROBE
HV-44
248
TROUBLESHOOTING
SELF-TEST
The Computer has a built-in self-test. To get the self-test
menu, hold the Option key down while turning the Com¬
puter On or type the word BYE and press the Return key if
the Computer is already On and in Basic. Press the Select
key to select the desired test, the Start key to start the test
and the Help key to go back to the self-test menu or the
Reset key to go back to Basic. The self-test will check the
ROM and RAM memory, audio, video and keyboard circuits.
When the Memory test is run, two bars will appear which
represent the Operating System ROM 1C (U5), then 48
squares will appear, each square representing IK of RAM
IC’s (U9 thru U16). While the ROM or RAM is being tested,
the color of the bar or square will be white, then change to
green if the ROM or RAM is good or red if the ROM or RAM
is bad.
When the Audio-Visual test is run, a music staff and treble
clef will appear on the screen. A tune of six tones is produc¬
ed with the corresponding note appearing on the screen
when that note is played. Sound channels 1 thru 4 Pokey 1C
(U22) are tested. An audio defect is indicated by a note ap¬
pearing on the screen with no sound. A video defect ANTIC
1C (U7) and GTIA 1C (U17) is indicated by a tone sounding
with no note appearing on the screen.
When the Keyboard test is run, the keyboard layout is
displayed on the screen. When a key is pressed the cor¬
responding key on the screen should change to inverse
video and a tone should sound. The Control and Shift keys
will work only when pressed along with another key. All
keys except the Reset, Help and Break keys are tested. IC’s
U17 and U22 are tested.
POWER SUPPLY
Unplug the Power Pack and check for 5.0V from pin 3 to pin
1 of Plug P7. If 5.0V is missing check Plug P7 and the cable
for possible open circuits. If the Plug P7 and cable check
good replace the Power Pack. Before plugging the new
Power Pack into the Computer, check for a possible short
from pin 3 to pin 1 of Jack J7 with the Power Switch (SI) in
the On position.
If the Power Pack checks good, plug it into the Computer,
turn the Computer On and check for 5.0V on the positive
end of Electrolytic C2. If 5.0V is missing check the Power
Switch (SI).
MICROPROCESSOR (CPU) OPERATION
Check the operation of the Reset Circuit at pin 8 of 1C U19.
Pin 8 should read a logic Low momentarily, then go logic
High and stay High when the Computer is turned On or the
Reset key is pressed. If the Reset reading is not correct
check Electrolytic C49, Diode CR1, Resistors R39 and R40
and 1C U19.
Verify the operation of the Clock Circuits by checking for a
1.78977MHz clock waveform at pin 11 of 1C U18. If the
waveform is missing or off frequency refer to the "Clock
and DIVIDERS" section of this Troubleshooting guide.
Check for pulses on the Address pins (pins 9 thru 20 and 22
thru 25) and Data pins (pins 26 thru 33) of the CPU 1C (U8). If
pulses are missing or one pin appears to be stuck at a logic
Low or High, turn the Computer Off, remove 1C U8, turn the
Computer back On and recheck the Address and Data pins.
The Address pins should read a logic Open and the Data
pins a logic High. Also, if pulses are missing with 1C U8 in
the Computer, check for pulses on the Data pins (pins 26
thru 33) of 1C U8 while turning the Computer On or pressing
the Reset key. If pulses appear, then suddenly stop, check
the Address Decoder 1C (U2), Memory Management Unit 1C
(U3), Operating System and Basic ROM IC’s (U4 and U5)and
CPU 1C (U8).

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