Jump to content

Atari 800 General Maintenance: Difference between revisions

From RetroTechCollection
← Older edit

Josh (talk | contribs)

5 user groups
7,584 edits
undo
VisualWikitext
Removed Category:Atari Maintenance Guides
Rebuild from Atari 400/800 Field Service Manual (hosted): C98-C103 'filter caps' do not exist; '+12V at 4050 pin 1' and '-5V at 4050 pin 8' are wrong (4050 runs on +5V, pin 8 is ground); the 400/800 have no OPTION-key self test. Added Atari's Section 6 symptom checklist, interlock switch S201, module-bay cooling change, Rev A/B ROM warning; cited throughout
 
(One intermediate revision by the same user not shown)
Line 1: Line 1:
<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />
[[File:Atari 800 (photo).jpg|thumb|right|300px|Atari 800]]
The '''[[Atari 800]]''' is the high-end half of Atari's 1979 pair and the only 8-bit Atari with a four-slot modular memory bay and a right-hand cartridge slot.<ref name="faq">Michael Current (ed.), ''comp.sys.atari.8bit Frequently Asked Questions'', sections 1.2 and 1.3. [http://www.faqs.org/faqs/atari-8-bit/faq/ Archived text]. Community reference; used here for model differences, module types, production history and the late-production cooling change, not for component values.</ref> That modularity is the machine's great strength for a restorer — almost everything is a plug-in board — and also its most common fault, because every one of those boards depends on an edge connector that has been oxidising since 1979.


<templatestyles src="Template:StyledTable/styles.css" />
Designators, part numbers and voltages on this page come from Atari's own field service manual.<ref name="fsm">Atari, Inc., ''ATARI Home Computer Field Service Manual 400/800'', June 1982. Hosted on this wiki: [[:File:Atari 400 800 Field Service Manual June 82.pdf]]. Sections 1 (theory of operation), 6 (symptom checklist), 7 (800 diagnostic flowcharts), 9 (800 parts list) and 10 (service bulletins).</ref>
[[File:Atari 800 mainboard and daughterboard.jpg|thumb|Atari 800 Mainboard (Rev C)]]
The '''Atari 800''' is a landmark 8-bit computer, prized for its robust construction and modular design. Decades of ageing, however, bring risks from dust, leaky capacitors, oxidised connectors, and brittle plastics. Proper maintenance is essential to keep your Atari 800 running reliably for years to come.


== Regular Cleaning ==
== Regular cleaning ==


=== External Case and Keyboard ===
=== Case and keyboard ===
* Wipe the ABS plastic case with a '''damp microfibre cloth''' and mild dish soap. Avoid harsh chemicals.
* Wipe the case with a damp microfibre cloth and mild soap; avoid solvents.
* For yellowed plastics, '''retrobrite''' is possible, but monitor temperature and exposure to prevent warping.
* The 800 has a full-stroke keyboard. Keycaps lift off vertically for cleaning; clean the plungers and contacts with 99 % isopropyl alcohol and let everything dry fully.
* Remove keycaps vertically for deep cleaning. Clean key plungers and contacts with 99% isopropyl alcohol (IPA).
* Inspect the keyboard ribbon where it flexes. Broken conductors in the ribbon, not failed switches, are the usual cause of a dead row.
* Lubricate stabiliser wires with plastic-safe grease if keys feel stiff.


=== Internal Cleaning ===
=== Internal cleaning ===
* Unplug the Atari 800 and allow a few minutes for capacitors to discharge.
* Unplug the adaptor and allow a few minutes for C207 and C208 (4700 µF each) on the supply board to discharge.
* Remove the top cover and metal RF shield to access the mainboard.
* Lift the module bay cover and remove the ROM and RAM modules. Remove the shield casting to reach the motherboard.
* Use compressed air or an anti-static brush to remove dust from the PCB, cartridge slots, and module bays.
* Blow out dust with compressed air or brush it away with an anti-static brush.
* For stubborn grime, use IPA and a soft ESD-safe brush. Ensure all parts are dry before reassembly.
* Reseat every module and socketed chip to wipe oxidised contacts.
* Re-seat all socketed modules (CPU, RAM, ROM) to wipe oxidised contacts.


== Power Supply & Voltage Checks ==
== Power supply and voltage checks ==


The original Atari 800 uses an external linear power supply (“brick”) delivering '''9V AC''' (3A). Ageing PSUs may drift out of spec, risking damage to internal voltage regulators and logic ICs.
The 800 is powered by an external '''transformer''' — Atari part '''C014319''', shared with the [[Atari 400]] — supplying '''9 V AC'''. It is not a DC supply; rectification and regulation happen inside the machine on the power supply PCB (CA014171).<ref name="fsm" />


{| class="wikitable styled-table" style="width:70%;"
* Measure the adaptor with the meter on '''AC volts'''. A reading near 9 V AC unloaded is what you expect.
! Pin !! Function !! Healthy Range
* The ON/OFF switch S202 opens the 9 V AC input, not a DC rail.<ref name="fsm" />
* CR206–CR209 (MR501) are the rectifier diodes; the regulators are '''A202 (5 V, C014348)''' and '''A201 (12 V, C014349)''' on heatsink assembly CA014708.<ref name="fsm" />
 
=== The rails ===
 
Atari states that the power supply PCB "receives 9 VAC from an external power adaptor (transformer) and provides +5 Vdc, +12 Vdc, and −5 Vdc for the Console system":<ref name="fsmps">Atari, Inc., ''ATARI Home Computer Field Service Manual 400/800'', June 1982, page 1-6, "Power Supply".</ref>
 
{| class="wikitable styled-table" style="width:80%;"
|+ Atari 800 supply rails
! Rail !! Purpose
|-
| +5 V A || Supply voltage for the logic PCBs
|-
| +5 V B || Specially filtered supply for the video circuitry
|-
|-
| Barrel centre || 9V AC || 9.0 – 10.5V rms
| +12 V || Supply for the dynamic RAM chips, and SIO pin 12
|-
|-
| Barrel sleeve || GND || 0V
| −5 V || Supply for the dynamic RAM chips
|}
|}


* '''Always measure output voltage with a multimeter before connecting.'''
'''Atari's manual does not print a test-point table of expected rail voltages for the 800.''' Measure at the regulator tabs and at the large filter capacitors on the power supply PCB rather than at arbitrary logic pins; published "test point" tables for this machine that name a CD4050 pin as the +12 V or −5 V point are wrong, because the 4050 runs from +5 V and its pin 8 is ground.
* If the PSU is warm when idle, hums, or reads above 11V AC, replace or rebuild it.
* Modern replacements (e.g., Meanwell AC adapters with proper rating) are recommended for safety.


=== Internal Voltage Rails ===
What Atari ''does'' specify is the clock chain:<ref name="fsmclock">Atari, Inc., ''ATARI Home Computer Field Service Manual 400/800'', June 1982, Table 5-1, "Clock Circuit", page 5-36.</ref>
The Atari 800 generates regulated DC voltages internally:


{| class="wikitable styled-table" style="width:80%; text-align:center;"
{| class="wikitable styled-table" style="width:80%; text-align:center;"
! Rail !! Test Point / IC Pin !! Expected Value
|+ Clock check points (Atari Table 5-1)
! Point !! Board !! Frequency (MHz)
|-
| Pin 21 of J101 || CPU card || 1.789
|-
| Pin 37 of A303 (6502) || CPU card || 1.140
|-
|-
| +5V DC || 6502 pin 8 || 4.95 – 5.20V
| Pin 35 of A302 (ANTIC) || CPU card || 3.579
|-
|-
| +12V DC || 4050 pin 1 || 11.8 – 12.3V
| Pin 29 of A301 (GTIA) || CPU card || 3.579
|-
|-
| -5V DC || 4050 pin 8 || -4.8 – -5.2V
| Collector of Q102 || Motherboard || 3.579
|-
| Pin 7 of A101 (POKEY) || Motherboard || 1.789
|-
| Pin 25 of A102 (PIA) || Motherboard || 1.789
|}
|}


* Test at the mainboard edge connector or directly at IC pins.
=== The interlock switch ===
* If rails are out of spec, suspect the 7805/7812/7905 regulators or input capacitors.
 
'''S201 is a power interlock switch''' on the power supply PCB: it breaks power to the system when the top panel is opened to fit or remove cartridges.<ref name="fsm" /> An 800 that is dead on the bench with the lid open, or that cuts out when the lid is disturbed, is very often this switch. Check it before the supply.
 
== Connector and socket corrosion ==


== Connector & Socket Corrosion ==
The 800's modular design means it lives or dies by its connectors:


The Atari 800’s modular design relies on edge connectors and sockets, which can oxidise over time.
* '''Module bay slots.''' Slot 1 takes the ROM personality module; the other three take RAM modules. Clean the module edge fingers with isopropyl alcohol and a lint-free cloth, then reseat several times.
* '''Cartridge slots''', left and right. The right slot is unique to the 800.<ref name="faq" />
* '''SIO port''' — J204, 13-pin, on the power supply PCB.<ref name="fsm" />
* '''Monitor socket''' — J205, a DIN socket on the power supply PCB.<ref name="fsm" />
* '''Four controller jacks.''' The 400 and 800 are the only 8-bit Ataris with four.<ref name="faq" />
* '''Power jack''' J206, and the keyboard ribbon connector.
* '''IC sockets''' on the CPU card (A301–A303, 40-pin) and the ROM and RAM modules.


=== Areas to Inspect ===
== Capacitors ==
* '''Cartridge slots (left/right)'''
* '''CPU, RAM, and ROM module sockets'''
* '''Keyboard ribbon connector'''
* '''SIO (Serial I/O) port'''
* '''Power input barrel jack'''


* Clean edge connectors with IPA and a pink pencil eraser.
Ten aluminium electrolytics exist in an 800. Eight are on the power supply PCB — C201, C202 (470 µF 16 V), C204, C205 (2200 µF 16 V), C207, C208 (4700 µF 16 V) and C210, C211 (10 µF 16 V) — and two on the motherboard, C179 and C199, both 10 µF 16 V.<ref name="fsm" /> The CPU card, ROM module and RAM modules contain none at all. Everything else is ceramic, mylar or polyester film.
* Apply '''DeoxIT''' or similar contact cleaner to sockets and re-seat modules.
* Inspect for green/white corrosion, especially if stored in humid environments.


== Capacitor Health & Replacement ==
Full designator table with packages, part numbers and a note on the revision difference in C207/C208's voltage rating: [[Atari 800 Capacitor Replacement Guide]].


While the Atari 800 is less prone to catastrophic capacitor failure than later machines, original electrolytics are now over 40 years old and may dry out or leak.
== Common failure points ==


=== Key Capacitors to Check/Replace ===
Atari's own symptom checklist for the 400 and 800. A1xx/Z1xx designators are on the motherboard, A2xx/C2xx on the power supply PCB, A3xx on the CPU card and A4xx on the ROM personality module.<ref name="fsmsym">Atari, Inc., ''ATARI Home Computer Field Service Manual 400/800'', June 1982, Section 6, "Symptom Checklist", pages 6-1 and 6-2.</ref>
{| class="wikitable styled-table" style="width:90%; text-align:center;"
 
! Location !! Value !! Function !! Notes
{| class="wikitable styled-table" style="width:100%;"
|+ Atari 400/800 symptom checklist (Atari Section 6)
! Symptom !! Possible cause
|-
| Snowy screen || Switch box, AC adaptor, channel select switch, modulator adjustment, RF cable damage
|-
| Black/grey screen || Verify +5 V, −5 V and +12 V supplies; CR201–CR209, C201–C205, C210, A201, A302, A303, A301, A103, A111, Z103–Z105, Q103–Q104, X101
|-
| Green/yellow screen || Z103–Z105, A103, Z303, Z304 — all on the ROM board
|-
| Solid blue screen || A101 (POKEY), Q107, X101
|-
| No colour or bad colour bars || R309 adjustment, A301–A302 on the CPU card; A111, Q107 on the motherboard; X101, Q103, Q104
|-
| No grey bars || A301, A111, Q107; R309 adjustment; X101, Q103, Q104; modulator
|-
| Upside-down alphanumerics or player field || A302 on the CPU card, A301, A111, Q107
|-
| Some keyboard keys fail || Keyboard failure
|-
| All keyboard keys fail || A101 (POKEY), Z103, Z104
|-
| Tones missing during sound or games || A101, R160, R161, R166, R170, C164, C179, C184, Q105, L101, Q106, L118, A203
|-
|-
| C98, C99 (mainboard) || 2200 µF / 16V || +5V & +12V smoothing || Replace if bulging or ESR is high
| Console (game) switches will not function || A301 on the CPU card, R119–R122, C121–C124
|-
|-
| C100, C101 || 470 µF / 25V || Regulator input filtering || Replace if leaking
| ROM test failed || A401–A403 on the ROM board, Z403
|-
|-
| C102, C103 || 10 µF / 16V || Audio & reset decoupling || Replace if audio is noisy
| RAM test failed || See Atari's RAM test matrix, Figure and Table 5-2
|-
|-
| Power LED || 1 µF / 16V || LED filter || Rarely fails, but easy to replace
| Hand controllers will not work || See Atari's Port Test matrix, Table 5-3
|}
|}


* Use high-quality, low-ESR electrolytics rated for 105 °C.
=== Memory and ROM modules ===
* Inspect for leakage, bulging, or crusty residue.
Slot 1 holds the CX801 (NTSC) or CX801.P (PAL) 10 KB ROM personality module; the remaining three slots take CX852 8 KB or CX853 16 KB RAM modules.<ref name="faq" /> Boot errors, random crashes and self-test memory errors are far more often a dirty module edge or a tired slot than a failed DRAM. Clean, reseat, and swap modules between slots to see whether the fault follows the module or stays with the slot.
* If video is unstable or the machine randomly resets, suspect failing capacitors.


== Common Failure Points ==
Atari prints a RAM test matrix (Figure and Table 5-2) that maps each failing bit reported by the SALT II cartridge to a specific chip position on the 8 KB and 16 KB cards; use it rather than guessing.<ref name="fsmram">Atari, Inc., ''ATARI Home Computer Field Service Manual 400/800'', June 1982, Figure and Table 5-2, "Defective RAM Identifier", page 5-39.</ref>


=== Voltage Regulators (7805, 7812, 7905) ===
=== Heat and the module bay ===
* Regulators dissipate significant heat and may develop cracked solder joints or fail outright.
Early 800s shipped with plastic cases around the ROM and RAM modules and two thumb tabs on the bay cover. On later machines, which had 48 KB as standard, '''Atari removed the module cases to improve cooling''', fitting instead a small plastic strip across the tops of the cards to hold them in position, and replaced the thumb tabs with screws.<ref name="faq" /> If you have a late machine, that bare-card appearance is correct and original, not a previous owner's bodge. The 800 has no fan and relies on passive airflow through the case and the shield castings, so keep the vents clear and do not run one in a closed cabinet.
* '''Symptoms:''' No power, unstable operation, or overheating.
* Reflow solder joints and add small heatsinks if running hot.


=== RAM Module Failures ===
=== CPU card ===
* The 16K RAM cards are socketed and prone to poor contact or chip failure.
A301 is the video chip, A302 is ANTIC and A303 is the 6502. Early machines have the CTIA (C012295) at A301; most have the GTIA (C014805). Atari's Upgrade Bulletin 1 covers the swap and notes that GTIA-specific software will not display correctly on a CTIA machine.<ref name="fsmub1">Atari, Inc., Consumer Product Service Upgrade Bulletin number 1, "GTIA Chip", 28 May 1982, reproduced in Section 10 of the ''ATARI Home Computer Field Service Manual 400/800''.</ref> Late-production 800s use a revised CPU board carrying Atari's SALLY 6502.<ref name="faq" />
* '''Symptoms:''' Boot errors, random crashes, or self-test memory errors.
* Clean contacts, re-seat modules, or swap with known-good RAM.


=== Keyboard Issues ===
=== Operating system ROMs — do not mix revisions ===
* Ribbon cable can become brittle or develop broken traces.
{{Warning|On the 800 the OS ROMs sit at '''A401 (C014599)''' and '''A403 (C012499)''' on the ROM personality module. Atari's Tech Tip 2 states that Revision A and Revision B ROMs must not be mixed: "When replacing these components, do not mix revision levels. System will not operate if Revision A is paired with Revision B." Revision B parts carry a copyright symbol followed by 1981 Atari.}}
* Key switches may oxidise internally.
* '''Symptoms:''' Dead keys, stuck keys, or keyboard not detected.
* Repair or replace ribbon; clean switch contacts with IPA.


=== SIO Port Problems ===
The same bulletin tells the technician to replace the ROM pair if a printer "overprints (hiccups)".<ref name="fsmtt2">Atari, Inc., Consumer Product Service Tech Tip number 2, "Revision B, Operating System ROMS", 28 May 1982, reproduced in Section 10 of the ''ATARI Home Computer Field Service Manual 400/800''.</ref>
* SIO (Serial I/O) port is used for disk drives, printers, etc.
* Oxidation or cracked solder joints can cause device detection issues.
* Clean pins and reflow solder as needed.


=== Cartridge Slot Failures ===
=== Faults that are not the computer ===
* Dust or oxidation leads to intermittent game or BASIC cartridge detection.
* '''The adaptor.''' A transformer that has been plugged in for forty years.
* Clean edge connectors and inspect for bent pins.
* '''The SIO cable or a peripheral.''' Unplug everything from SIO and retest before opening the case.
* '''A cartridge.''' Dirty cartridge contacts produce lock-ups and garbage screens that look exactly like board faults. With no cartridge and no powered disk drive, an 800 should come up in Memo Pad mode.<ref name="faq" />
* '''The TV switch box and RF cable.''' Atari's checklist puts these first for a snowy screen, ahead of anything inside the machine.<ref name="fsmsym" />


== Device-Specific Subsystems ==
== Diagnostics ==


=== RF Modulator ===
The 400 and 800 have '''no built-in self test'''; holding OPTION at power-on does nothing on these models, because that is XL-series behaviour. Atari's field procedure is the SALT II diagnostic cartridge, and Sections 3 and 7 of the field service manual are written around it — colour bar, grey bar, keyboard, tone, console switch, ROM verify, RAM and port tests, each with a flowchart.<ref name="fsm" /> With no cartridge and no powered drive attached, a healthy 800 boots to Memo Pad.<ref name="faq" />
* The RF modulator contains small electrolytic capacitors that may fail, causing poor video or no output.
* If composite video is used, consider bypassing or recapping the modulator.


=== Cooling and Ventilation ===
== Recommended tools ==
* The Atari 800 has no internal fan but relies on passive airflow.
* Ensure vents are clear of dust and obstructions.
* For hot climates, consider adding a low-noise 5V fan powered from the regulator output.


=== Power Switch ===
See [[Recommended Tools]]. Specific to this machine: a meter that reads AC volts for the adaptor, contact cleaner for the module slots, and a load resistor for discharging C207 and C208.
* The mechanical power switch can oxidise or wear out.
* If the machine fails to power on, test continuity across the switch and clean or replace as needed.


== Recommended Tools & Consumables ==
== Preventive maintenance checklist ==


* ESD wrist strap and anti-static mat
# Test the adaptor on the AC range.
* Digital multimeter (for PSU and voltage checks)
# Check and clean the interlock switch S201 and the power switch S202.
* Soldering iron with fine tip and quality solder
# Reseat the ROM and RAM modules and clean their edge fingers.
* Desoldering braid or pump (for capacitor and regulator work)
# Clean both cartridge slots and the SIO connector.
* Isopropyl alcohol (99%) and soft brushes
# Replace the power supply PCB electrolytics if they are original (see [[Atari 800 Capacitor Replacement Guide]]).
* DeoxIT or similar contact cleaner
# Inspect the keyboard ribbon for cracked conductors.
* Pink pencil eraser (for edge connectors)
# Keep the vents clear; the 800 has no fan.
* Small Phillips and flathead screwdrivers
* Spudger or plastic pry tool (for opening case)
* Replacement electrolytic capacitors (see above table)
* Optional: Freeze spray for thermal fault diagnosis


== Preventive Maintenance Checklist ==
== Related pages ==
* [[Atari 800]]
* [[Atari 800 Capacitor Replacement Guide]]
* [[Atari 800 Troubleshooting Guide]]
* [[Atari 400 General Maintenance]]
* [[Recommended Tools]]


# '''Test PSU output''' before every session; replace if voltage is out of spec.
== References ==
# '''Inspect and reflow voltage regulator solder joints''' annually.
<references />
# '''Re-seat all socketed modules''' and clean contacts.
# '''Replace main electrolytic capacitors''' if original or showing signs of failure.
# '''Clean cartridge and SIO connectors''' with IPA and eraser.
# '''Check keyboard ribbon for cracks''' and repair or replace if needed.
# '''Ensure ventilation slots are clear''' and consider passive cooling enhancements.
# '''Store the Atari 800 in a dry, dust-free environment''' to minimise corrosion.


== Quick-Fix Flowcharts ==
[[Category:Atari Systems]]
 
[[Category:Maintenance Guides]]
=== No Video / No Power ===
* Check PSU output → OK?
* Confirm power switch continuity.
* Measure +5V and +12V rails at mainboard.
* If dead, suspect voltage regulators or main filter capacitors.
* If power LED is on but no video, check RF modulator and video output path.
 
=== Boot Errors / Memory Failures ===
* Run built-in self-test (hold OPTION on power-up).
* If RAM errors, re-seat RAM modules and clean contacts.
* Swap suspect RAM cards with known-good modules.
* If persistent, check for corroded sockets or failed RAM ICs.


=== Keyboard Not Responding ===
{{Navbox-AtariVintageComputers|state=collapsed}}
* Inspect ribbon cable for breaks.
* Clean keyboard connector and re-seat.
* Test individual key switches with continuity meter.
 
=== Cartridge Not Detected ===
* Clean cartridge edge and slot contacts.
* Inspect for bent or missing pins.
* Try alternate cartridge slot.
 
== Related Maintenance Guides ==
* [[Atari 800 Capacitor Replacement Guide]]
* [[Atari 800 Troubleshooting Guide|Atari 800 Troubleshooting]]
* [[Atari SIO Device Maintenance]]
[[Category:Atari Systems]]

Latest revision as of 22:21, 22 September 2026

Atari 800

The Atari 800 is the high-end half of Atari's 1979 pair and the only 8-bit Atari with a four-slot modular memory bay and a right-hand cartridge slot.[1] That modularity is the machine's great strength for a restorer — almost everything is a plug-in board — and also its most common fault, because every one of those boards depends on an edge connector that has been oxidising since 1979.

Designators, part numbers and voltages on this page come from Atari's own field service manual.[2]

Regular cleaning

[edit | edit source]

Case and keyboard

[edit | edit source]
  • Wipe the case with a damp microfibre cloth and mild soap; avoid solvents.
  • The 800 has a full-stroke keyboard. Keycaps lift off vertically for cleaning; clean the plungers and contacts with 99 % isopropyl alcohol and let everything dry fully.
  • Inspect the keyboard ribbon where it flexes. Broken conductors in the ribbon, not failed switches, are the usual cause of a dead row.

Internal cleaning

[edit | edit source]
  • Unplug the adaptor and allow a few minutes for C207 and C208 (4700 µF each) on the supply board to discharge.
  • Lift the module bay cover and remove the ROM and RAM modules. Remove the shield casting to reach the motherboard.
  • Blow out dust with compressed air or brush it away with an anti-static brush.
  • Reseat every module and socketed chip to wipe oxidised contacts.

Power supply and voltage checks

[edit | edit source]

The 800 is powered by an external transformer — Atari part C014319, shared with the Atari 400 — supplying 9 V AC. It is not a DC supply; rectification and regulation happen inside the machine on the power supply PCB (CA014171).[2]

  • Measure the adaptor with the meter on AC volts. A reading near 9 V AC unloaded is what you expect.
  • The ON/OFF switch S202 opens the 9 V AC input, not a DC rail.[2]
  • CR206–CR209 (MR501) are the rectifier diodes; the regulators are A202 (5 V, C014348) and A201 (12 V, C014349) on heatsink assembly CA014708.[2]

The rails

[edit | edit source]

Atari states that the power supply PCB "receives 9 VAC from an external power adaptor (transformer) and provides +5 Vdc, +12 Vdc, and −5 Vdc for the Console system":[3]

Atari 800 supply rails
Rail Purpose
+5 V A Supply voltage for the logic PCBs
+5 V B Specially filtered supply for the video circuitry
+12 V Supply for the dynamic RAM chips, and SIO pin 12
−5 V Supply for the dynamic RAM chips

Atari's manual does not print a test-point table of expected rail voltages for the 800. Measure at the regulator tabs and at the large filter capacitors on the power supply PCB rather than at arbitrary logic pins; published "test point" tables for this machine that name a CD4050 pin as the +12 V or −5 V point are wrong, because the 4050 runs from +5 V and its pin 8 is ground.

What Atari does specify is the clock chain:[4]

Clock check points (Atari Table 5-1)
Point Board Frequency (MHz)
Pin 21 of J101 CPU card 1.789
Pin 37 of A303 (6502) CPU card 1.140
Pin 35 of A302 (ANTIC) CPU card 3.579
Pin 29 of A301 (GTIA) CPU card 3.579
Collector of Q102 Motherboard 3.579
Pin 7 of A101 (POKEY) Motherboard 1.789
Pin 25 of A102 (PIA) Motherboard 1.789

The interlock switch

[edit | edit source]

S201 is a power interlock switch on the power supply PCB: it breaks power to the system when the top panel is opened to fit or remove cartridges.[2] An 800 that is dead on the bench with the lid open, or that cuts out when the lid is disturbed, is very often this switch. Check it before the supply.

Connector and socket corrosion

[edit | edit source]

The 800's modular design means it lives or dies by its connectors:

  • Module bay slots. Slot 1 takes the ROM personality module; the other three take RAM modules. Clean the module edge fingers with isopropyl alcohol and a lint-free cloth, then reseat several times.
  • Cartridge slots, left and right. The right slot is unique to the 800.[1]
  • SIO port — J204, 13-pin, on the power supply PCB.[2]
  • Monitor socket — J205, a DIN socket on the power supply PCB.[2]
  • Four controller jacks. The 400 and 800 are the only 8-bit Ataris with four.[1]
  • Power jack J206, and the keyboard ribbon connector.
  • IC sockets on the CPU card (A301–A303, 40-pin) and the ROM and RAM modules.

Capacitors

[edit | edit source]

Ten aluminium electrolytics exist in an 800. Eight are on the power supply PCB — C201, C202 (470 µF 16 V), C204, C205 (2200 µF 16 V), C207, C208 (4700 µF 16 V) and C210, C211 (10 µF 16 V) — and two on the motherboard, C179 and C199, both 10 µF 16 V.[2] The CPU card, ROM module and RAM modules contain none at all. Everything else is ceramic, mylar or polyester film.

Full designator table with packages, part numbers and a note on the revision difference in C207/C208's voltage rating: Atari 800 Capacitor Replacement Guide.

Common failure points

[edit | edit source]

Atari's own symptom checklist for the 400 and 800. A1xx/Z1xx designators are on the motherboard, A2xx/C2xx on the power supply PCB, A3xx on the CPU card and A4xx on the ROM personality module.[5]

Atari 400/800 symptom checklist (Atari Section 6)
Symptom Possible cause
Snowy screen Switch box, AC adaptor, channel select switch, modulator adjustment, RF cable damage
Black/grey screen Verify +5 V, −5 V and +12 V supplies; CR201–CR209, C201–C205, C210, A201, A302, A303, A301, A103, A111, Z103–Z105, Q103–Q104, X101
Green/yellow screen Z103–Z105, A103, Z303, Z304 — all on the ROM board
Solid blue screen A101 (POKEY), Q107, X101
No colour or bad colour bars R309 adjustment, A301–A302 on the CPU card; A111, Q107 on the motherboard; X101, Q103, Q104
No grey bars A301, A111, Q107; R309 adjustment; X101, Q103, Q104; modulator
Upside-down alphanumerics or player field A302 on the CPU card, A301, A111, Q107
Some keyboard keys fail Keyboard failure
All keyboard keys fail A101 (POKEY), Z103, Z104
Tones missing during sound or games A101, R160, R161, R166, R170, C164, C179, C184, Q105, L101, Q106, L118, A203
Console (game) switches will not function A301 on the CPU card, R119–R122, C121–C124
ROM test failed A401–A403 on the ROM board, Z403
RAM test failed See Atari's RAM test matrix, Figure and Table 5-2
Hand controllers will not work See Atari's Port Test matrix, Table 5-3

Memory and ROM modules

[edit | edit source]

Slot 1 holds the CX801 (NTSC) or CX801.P (PAL) 10 KB ROM personality module; the remaining three slots take CX852 8 KB or CX853 16 KB RAM modules.[1] Boot errors, random crashes and self-test memory errors are far more often a dirty module edge or a tired slot than a failed DRAM. Clean, reseat, and swap modules between slots to see whether the fault follows the module or stays with the slot.

Atari prints a RAM test matrix (Figure and Table 5-2) that maps each failing bit reported by the SALT II cartridge to a specific chip position on the 8 KB and 16 KB cards; use it rather than guessing.[6]

Heat and the module bay

[edit | edit source]

Early 800s shipped with plastic cases around the ROM and RAM modules and two thumb tabs on the bay cover. On later machines, which had 48 KB as standard, Atari removed the module cases to improve cooling, fitting instead a small plastic strip across the tops of the cards to hold them in position, and replaced the thumb tabs with screws.[1] If you have a late machine, that bare-card appearance is correct and original, not a previous owner's bodge. The 800 has no fan and relies on passive airflow through the case and the shield castings, so keep the vents clear and do not run one in a closed cabinet.

CPU card

[edit | edit source]

A301 is the video chip, A302 is ANTIC and A303 is the 6502. Early machines have the CTIA (C012295) at A301; most have the GTIA (C014805). Atari's Upgrade Bulletin 1 covers the swap and notes that GTIA-specific software will not display correctly on a CTIA machine.[7] Late-production 800s use a revised CPU board carrying Atari's SALLY 6502.[1]

Operating system ROMs — do not mix revisions

[edit | edit source]

The same bulletin tells the technician to replace the ROM pair if a printer "overprints (hiccups)".[8]

Faults that are not the computer

[edit | edit source]
  • The adaptor. A transformer that has been plugged in for forty years.
  • The SIO cable or a peripheral. Unplug everything from SIO and retest before opening the case.
  • A cartridge. Dirty cartridge contacts produce lock-ups and garbage screens that look exactly like board faults. With no cartridge and no powered disk drive, an 800 should come up in Memo Pad mode.[1]
  • The TV switch box and RF cable. Atari's checklist puts these first for a snowy screen, ahead of anything inside the machine.[5]

Diagnostics

[edit | edit source]

The 400 and 800 have no built-in self test; holding OPTION at power-on does nothing on these models, because that is XL-series behaviour. Atari's field procedure is the SALT II diagnostic cartridge, and Sections 3 and 7 of the field service manual are written around it — colour bar, grey bar, keyboard, tone, console switch, ROM verify, RAM and port tests, each with a flowchart.[2] With no cartridge and no powered drive attached, a healthy 800 boots to Memo Pad.[1]

[edit | edit source]

See Recommended Tools. Specific to this machine: a meter that reads AC volts for the adaptor, contact cleaner for the module slots, and a load resistor for discharging C207 and C208.

Preventive maintenance checklist

[edit | edit source]
  1. Test the adaptor on the AC range.
  2. Check and clean the interlock switch S201 and the power switch S202.
  3. Reseat the ROM and RAM modules and clean their edge fingers.
  4. Clean both cartridge slots and the SIO connector.
  5. Replace the power supply PCB electrolytics if they are original (see Atari 800 Capacitor Replacement Guide).
  6. Inspect the keyboard ribbon for cracked conductors.
  7. Keep the vents clear; the 800 has no fan.
[edit | edit source]

References

[edit | edit source]
  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Michael Current (ed.), comp.sys.atari.8bit Frequently Asked Questions, sections 1.2 and 1.3. Archived text. Community reference; used here for model differences, module types, production history and the late-production cooling change, not for component values.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982. Hosted on this wiki: File:Atari 400 800 Field Service Manual June 82.pdf. Sections 1 (theory of operation), 6 (symptom checklist), 7 (800 diagnostic flowcharts), 9 (800 parts list) and 10 (service bulletins).
  3. ↑ Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, page 1-6, "Power Supply".
  4. ↑ Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, Table 5-1, "Clock Circuit", page 5-36.
  5. ↑ 5.0 5.1 Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, Section 6, "Symptom Checklist", pages 6-1 and 6-2.
  6. ↑ Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, Figure and Table 5-2, "Defective RAM Identifier", page 5-39.
  7. ↑ Atari, Inc., Consumer Product Service Upgrade Bulletin number 1, "GTIA Chip", 28 May 1982, reproduced in Section 10 of the ATARI Home Computer Field Service Manual 400/800.
  8. ↑ Atari, Inc., Consumer Product Service Tech Tip number 2, "Revision B, Operating System ROMS", 28 May 1982, reproduced in Section 10 of the ATARI Home Computer Field Service Manual 400/800.



Retrieved from "https://wiki.retrotechcollection.com/index.php?title=Atari_800_General_Maintenance&oldid=12285"