Atari 800 General Maintenance
.jpg)
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]
| 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]
| 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]
| 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] | 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. |
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]
Recommended tools
[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]- Test the adaptor on the AC range.
- Check and clean the interlock switch S201 and the power switch S202.
- Reseat the ROM and RAM modules and clean their edge fingers.
- Clean both cartridge slots and the SIO connector.
- Replace the power supply PCB electrolytics if they are original (see Atari 800 Capacitor Replacement Guide).
- Inspect the keyboard ribbon for cracked conductors.
- Keep the vents clear; the 800 has no fan.
Related pages
[edit | edit source]- Atari 800
- Atari 800 Capacitor Replacement Guide
- Atari 800 Troubleshooting Guide
- Atari 400 General Maintenance
- Recommended Tools
References
[edit | edit source]- ↑ 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.
- ↑ 2.0 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).
- ↑ Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, page 1-6, "Power Supply".
- ↑ Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, Table 5-1, "Clock Circuit", page 5-36.
- ↑ 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.
- ↑ Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, Figure and Table 5-2, "Defective RAM Identifier", page 5-39.
- ↑ 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.
- ↑ 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.