Editing Atari 800XL General Maintenance

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[[File:Atari 800XL (photo).jpg|thumb|right|300px|Atari 800XL]]
Maintenance guide for the '''[[Atari 800XL]]'''. The 800XL is a single-board, single-rail machine: one external +5 V supply, one PCB, and a set of socketed ICs. That makes it one of the more approachable 8-bit machines to keep alive, and it means most of what fails is a contact, a supply or a chip rather than anything subtle.

Designators, part numbers and figures on this page come from Atari's own service manual.<ref name="sm">Atari, Inc., ''Service Manual for the ATARI 800XL Computer''. Hosted on this wiki: [[:File:Atari 800XL Service Manual.pdf]]. Sections 1 (theory of operation), 2 (self testing), 3 (disassembly/assembly), 4 (troubleshooting) and 5 (schematic and parts list).</ref>

== Regular cleaning ==

=== Case and keyboard ===
* Unplug the supply and remove all cartridges and cables.
* Wipe the case with a damp microfibre cloth and mild soap; avoid abrasives and solvents.
* Keycaps lift vertically. Clean caps and plungers with 99 % isopropyl alcohol and let them dry fully.
* Take care with the '''keyboard ground strap''' when the top comes off — Atari's disassembly procedure calls it out specifically.<ref name="sm" />

=== Internal cleaning ===
* Allow a minute or two after power-off before working on the board.
* Remove dust from the PCB, the cartridge slot and the connectors with compressed air or an anti-static brush.
* Clean sticky residue with isopropyl alcohol.

=== Disassembly ===
Atari's sequence:<ref name="sm" />
# Turn the unit upside down and remove the '''six screws''' from the bottom cover.
# Turn it upright, tip the cover by raising the left side, disconnect the keyboard ground strap, and remove the keyboard cable from its socket.
# Remove the '''four remaining screws''' holding the PC board.
# Lift the front of the board while pushing out on the right (player-port) side of the bottom housing until the player ports clear it.

Atari adds a note worth keeping: '''do not interchange top or bottom housings between units''', because the mouldings are not interchangeable. Keep each machine's housings with that machine.<ref name="sm" />

== Power supply and voltage checks ==

The 800XL takes an external '''+5 V DC''' supply through a '''7-pin DIN''' connector — not a barrel jack. Atari's specification: 110 V AC nominal in, '''+5 V DC out ±2 %, 1.2 A maximum'''. The console parts list gives the supply as Atari part CA024814-001.<ref name="sm" />

'''±2 % of 5 V is 4.90 V to 5.10 V.''' Judge a brick by that, not by "about five volts".

{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+ Atari 800XL power connector (7-pin DIN, looking toward the computer)
! Pin !! Function
|-
| 1, 4, 6 || +5 volts
|-
| 3, 5, 7 || Ground return
|-
| 2 || Ground
|}

There is '''no +12 V and no −5 V''' anywhere in an 800XL, and no regulator on the board. Internally the +5 V input is distributed as '''+5 A, +5 B and +5 C''', the names Atari's troubleshooting section uses.<ref name="sm" />

{{Warning|Test the supply on its own before connecting it. Nothing on the 800XL board regulates or protects the rail: whatever the brick puts out goes straight to the 6502C, ANTIC, GTIA and POKEY. The original Atari bricks are sealed, potted units with no serviceable interior, and a drifting one is the most common way an XL machine kills its own custom chips.}}

=== Internal checks ===

{| class="wikitable styled-table" style="width:85%; text-align:center;"
|+ Supply pins on the custom chips
! Device !! Location !! VCC pin !! Ground pin
|-
| 6502C CPU || U8 || 8 || 1 and 21
|-
| ANTIC || U7 || 21 || 1
|-
| GTIA || U17 || 27 || 3
|-
| POKEY || U22 || 17 || 1
|}

Pin numbers from Atari's pin-assignment figures.<ref name="pins">Atari, Inc., ''ATARI 600XL Computer Field Service Manual'', Rev. 1, October 1983, figures 1-3 to 1-6. Hosted on this wiki: [[:File:Atari 600XL Field Service Manual.pdf]]. Cited for the VCC pin numbers of the custom chips; the 600XL and 800XL use the same devices and the 800XL manual reproduces the same figures.</ref> Note that '''pin 40 of the 6502C is RESET''', not the supply.

Atari also publishes output levels for the 5-pin DIN monitor jack (J2), which make a useful end-to-end check:<ref name="sm" />

{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+ Monitor output levels (J2)
! Signal !! Minimum !! Maximum
|-
| Composite video || 750 mV p-p || 1 V p-p
|-
| Composite luminance || 1.2 V p-p || 1.5 V p-p
|-
| Audio || 600 mV p-p || 750 mV p-p
|}

== Connector and socket corrosion ==

Inspect and clean:

* '''Cartridge slot''' (J4, 30-pin).
* '''SIO port''' (J1, 13-pin). On the 800XL, pin 10 is +5 V/Ready and '''pin 12 is not connected''' — the +12 V that the [[Atari 800]] provides on SIO pin 12 does not exist here, so 400/800-era peripherals that expect it need their own supply.<ref name="sm" />
* '''Controller jacks''' J5 and J6 (9-pin D-type). Pin 7 is +5 V.
* '''Monitor jack''' J2 and the '''7-pin DIN power inlet''' J7.
* '''Keyboard header''' J8 (24-pin) and the keyboard ground strap.
* '''IC sockets.''' Atari's parts list fits sockets at every IC position on the board except U6, U21 (both unused) and U29, the delay module — including all eight DRAMs, GTIA, POKEY and the PIA.<ref name="sm" />

Reseating socketed chips wipes the contacts and is the single highest-yield thing you can do to an intermittent XL. Do it before suspecting any chip.

== Capacitors ==

An 800XL contains '''twelve''' aluminium electrolytics: C1 (470 µF 10 V), C2, C3, C10 and C79 (22 µF 16 V), C19, C20 and C22 (4.7 µF 35 V non-polarised), C24, C50 and C98 (10 µF 16 V) and C49 (47 µF 10 V).<ref name="sm" /> Everything else on the board is ceramic. Atari's parts list marks C33, C56, C58–C61, C67, C99–C101, C103, C104, C110 and C111 as '''not used''' — there is nothing fitted at those positions.

Full table with part numbers and the disassembly sequence: [[Atari 800XL Capacitor Replacement Guide]].

== Chip map ==

{| class="wikitable styled-table" style="width:90%;"
|+ Atari 800XL integrated circuits (Atari parts list)
! Location !! Device !! Atari part number
|-
| U1 || LM358 dual op-amp || C061702
|-
| U2 || 74LS138 decoder || C061428
|-
| U3 || MMU 1B memory management unit || C061618
|-
| U4 || BASIC ROM Rev. B, 8K × 8 || C060302
|-
| U5 || OS ROM, 16K × 8 || C061598
|-
| U7 || ANTIC || C021697
|-
| U8 || 6502C CPU || C014806
|-
| U9–U16 || DRAM, 64K × 1 || C060612
|-
| U17 || GTIA || C014805
|-
| U18 || 74LS08 quad AND || C017097
|-
| U19 || 74LS14 hex inverter || C061850
|-
| U20 || CD4050B hex buffer || C010816
|-
| U22 || POKEY || C012294
|-
| U23 || PIA || C014795
|-
| U24, U25 || CD4051B multiplexer || C014336
|-
| U26, U27 || 74LS158 multiplexer || C014345
|-
| U28 || 74LS375 latch || C060619
|-
| U29 || Delay module || C060472
|-
| U30 || 74LS51 AND/OR inverter || C060474
|}

U6 and U21 are marked not used. Y1 is a 3.579545 MHz crystal (C061090 on domestic units).<ref name="sm" />

== Common failure points ==

Atari's own troubleshooting table, listed in its order of most common failure.<ref name="smts">Atari, Inc., ''Service Manual for the ATARI 800XL Computer'', Section 4, "Troubleshooting", pages 27–30.</ref>

{| class="wikitable styled-table" style="width:100%;"
|+ Atari 800XL troubleshooting table (Atari Section 4)
! Symptom !! Possible causes !! Solution
|-
| Snowy screen || TV switch box, ON/OFF switch, channel select switch, RF modulator; defective power supply or damaged RF cable; defective (open) components on the +5 C line; defective (shorted) components on the +5 A, B and/or C lines; shorted LSIs or ICs || Adjust, replace, or isolate and replace
|-
| No colour or bad colour || RF modulator or R38; U17, U20, Q1, Q3, CR2, CR3; Y1 || Adjust or replace; verify 3.579545 MHz at Y1
|-
| Black/grey screen || Y1, Q8, Q9, C109; U2, U7–U20, U22, U23, U26–U30 || Troubleshoot the clock circuit; isolate and replace the defective IC
|-
| Yellow screen || U28 || Replace
|-
| Blue screen || U2 || Replace
|-
| Red/brown screen || U2–U5, U18, U19, U28, U30 || Isolate and replace
|-
| CPU test fail || Y1, Q8, Q9, U8 || Verify the 3.58 MHz oscillator frequency
|-
| RAM test failed || U2, U3, U9–U16, U18, U19, U26–U30 || Verify ANTIC is Rev. E; repair or replace
|-
| ROM test failed || U2–U5 || Repair or replace
|-
| Video or ANTIC stress fail || U7 || Repair or replace
|-
| GTIA fail || U17 || Replace
|-
| No power light (L1) || Power LED, power supply, cables || Repair or replace
|-
| Console game switches will not function || U17, keyboard, cable || Repair or replace
|-
| Tone or tones missing during tone test || U22, 4.5 MHz audio carrier frequency, U1, TV volume || Repair; adjust 4.5 MHz on the RF modulator
|-
| No grey bars, or a missing bar || U17, U20 || Repair or replace
|-
| Upside-down alphanumerics on the player field || U7 || Replace
|-
| Some keyboard keys fail || U22, keyboard, U24, U25, cable || Repair or replace
|-
| All keyboard keys fail || U22, U24, U25 || Repair or replace
|-
| I/O port test — PIA ports || U23, C26–C29, C82–C92, L19–L22 || Repair or replace
|-
| I/O port test — SIO port || U22, U23, C75–C78 || Repair or replace
|-
| I/O port test — POT lines || U22, L15–L18, C71–C74, C63–C66 || Repair or replace
|-
| I/O port test — trigger lines || U17, L23, L30, C96, C97 || Repair or replace
|-
| I/O port test — controller jack voltage || L25, U5, J6 || Inspect J5 and J6 for damaged pins; replace as necessary
|-
| Timers || U22 || Replace
|}

The 2-way clock, external audio and I/O port tests require the Super SALT test assembly, jumper cables and a supply; the keyboard and switch tests need a person to press the keys.<ref name="smts" />

=== Sockets, not chips ===
Because every IC is socketed, an intermittent 800XL is far more likely to have an oxidised socket than a failed part. Random lock-ups, boots that work one time in three, and colour or graphics faults that come and go all respond to pulling each chip, cleaning its legs and reseating it. Do that before ordering a GTIA.

=== DRAM ===
The eight 64K × 1 DRAMs at U9–U16 are the most-replaced parts in the XL line, but Atari's own list for a RAM test failure is wider than the DRAMs alone — U2, U3, U18, U19 and U26–U30 are all in the path.<ref name="smts" /> Atari also tells the technician to '''verify that ANTIC is Rev. E''' when chasing a RAM failure.<ref name="smts" />

=== Faults that are not the computer ===
* '''The power supply.''' First suspect in almost every case.
* '''The SIO chain.''' Unplug every SIO peripheral and retest; one bad device or cable takes the whole bus down.
* '''A cartridge.''' A cartridge takes precedence over the built-in BASIC in hardware, so dirty cartridge contacts give blank screens and lock-ups that look like board faults. Test with the slot empty — a healthy 800XL comes up in Atari BASIC.
* '''The TV switch box and RF cable.''' Atari's table puts these first for a snowy screen, ahead of anything inside the machine.<ref name="smts" />

== Self test ==

Hold '''OPTION''' while switching on, with no cartridge fitted. The Self Test menu appears and offers a memory test (RAM, ROM and ANTIC), an audio/visual test (ANTIC, GTIA and POKEY), a keyboard test (POKEY and ANTIC) and "all tests". SYSTEM RESET exits to the BASIC ready prompt. Atari notes that the HELP key does nothing in this context except return from an individual test to the menu.<ref name="sm" />

== Recommended tools ==

See [[Recommended Tools]]. Specific to this machine: a multimeter you trust to a few tens of millivolts (to judge ±2 %), contact cleaner, and a known-good power supply to swap in.

== Preventive maintenance checklist ==

# Measure the power supply before a session; 4.90–5.10 V is the specification.
# Reseat all socketed ICs and clean the sockets.
# Clean the cartridge slot, SIO port and controller jacks.
# Inspect the keyboard ground strap and the keyboard cable.
# Reflow suspect solder joints on the power inlet, SIO and controller jacks.
# Replace the twelve electrolytics if they are original (see [[Atari 800XL Capacitor Replacement Guide]]).
# Keep vents clear; the 800XL has no fan.

== Related pages ==
* [[Atari 800XL]]
* [[Atari 800XL Capacitor Replacement Guide]]
* [[Atari 800XL Troubleshooting Guide]]
* [[Atari 600XL Troubleshooting Guide]]
* [[Recommended Tools]]

== References ==
<references />

[[Category:Atari Systems]]
[[Category:Maintenance Guides]]

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