Atari 800 General Maintenance

Atari 800

The Atari 800 is built from plug-in boards: a CPU board, a ROM personality module and up to three RAM modules sit in edge connectors on the motherboard, and a separate power supply board carries the regulators, the switches and the jacks. Most maintenance on the 800 is keeping those edge connectors clean and the supply board healthy.

Opening the machine

Atari's disassembly order (pp. 4-8 to 4-14):

1. Switch off. Open the cartridge door, turn the two door clamps outwards, lift the door assembly 1/4 inch, pull it towards you and lift it off. Lift out the RAM modules, the ROM module and any cartridges.
2. Turn the console upside down, remove the five bottom-cover screws and tilt the bottom cover off.
3. Remove the two screws in the aluminium casting flange and the screw at the lower left corner of the power supply board, and set the speaker aside.
4. Turn the console over, tilt the top cover back to 90°, unplug the keyboard ribbon and set the top cover aside. The keyboard is held in the top cover by four corner screws.
5. Lift the power supply board straight up; unplug the RF cable and the harness and remove its three screws.
6. For the CPU board, turn the unit over, remove the nine screws of the lower shield and lift the motherboard and shield out of the aluminium casting. The motherboard is held to the shield by four nylon clips; pry them off carefully and do not bend the motherboard connector pins.

Atari's notes for this section: do not mix screws, keep to 6 inch-pounds of torque into plastic and 10 inch-pounds into aluminium, work on a soft surface when the console is upside down, and take static precautions with every board. On reassembly the ROM module goes in the slot nearest the keyboard and up to three RAM modules in the others.

Early 800s have plastic cases on the ROM and RAM modules and thumb tabs on the cover over the slots. Later machines, with 48 KB as standard, have bare cards held by a plastic strip across their tops and a screwed-down cover. Jason Harmon, quoted in the FAQ, says the cases were dropped to improve cooling.

Cleaning the board contacts

Atari's procedure for the edge fingers of the CPU, RAM and ROM boards (pp. 4-20 and 4-21):

1. Inspect the contacts for flux, dirt, foreign material and deep scratches.
2. Clean both sides of the fingers with a dust-free cloth moistened with ZEP Safety Solvent or isopropyl alcohol, removing old lubricant. Do not touch the contacts afterwards.
3. If corrosion or residue remains, scrub with a board-cleaning brush and solvent, four to six firm strokes, and repeat step 2.
4. Apply an even coat of Lubriplate DS-ES to the fingers on both sides with an acid brush, thick enough to protect them from corrosion, and keep it off the rest of the board.

Inspection

Atari's visual inspection (p. 4-21):

• Controller and peripheral jacks: broken or bent pins.
• RF cable: cracked insulation, bare or pinched areas.
• Interlock switch: with the machine on and Memo Pad on screen, open the cartridge door, press the plunger down with a small screwdriver and release it. It must spring back to its open position, which powers the console down.
• Cartridge slots: foreign objects or damage.
• Power jack: bent or damaged pins.

The keyboard ribbon changed during production; Atari's parts list shows an early white ribbon and a later multicoloured one.

Power supply

The adaptor (Atari C014319) is a transformer delivering 9 V AC; measure it on the AC range. The power supply board (CA014171) rectifies it with the bridge CR206–CR209 (MR501) and regulates it with A202 (5 V, drawn as a 7805, C014348) and A201 (12 V, printed 78M12, C014349) on heatsink assembly CA014708.

Atari 800 supply rails

Rail	J201 pin	Purpose (Atari p. 1-6)
+5 V A	18, 19	Logic boards
+5 V B	17	Video circuitry, specially filtered
+12 V	21	Dynamic RAM; also SIO pin 12
−5 V	1	Dynamic RAM

The power switch S202 and the interlock S201 are both in the 9 V AC input. Atari's flowcharts check that each rail is present at J201 and print no tolerance band; the checks and the parts they point to are on the Atari 800 Troubleshooting Guide.

The clock can be checked with a scope against Atari's Table 7-1: 1.789 MHz at pins 21 and 22 of the CPU board connector J101, 3.579 MHz at ANTIC (A302) pin 35 and GTIA (A301) pins 28 and 29 and at the collector of Q102 on the motherboard, and 1.789 MHz at POKEY (A101) pin 7 and PIA (A102) pin 25.

Capacitors

The 800 has ten aluminium electrolytics. Eight are on the power supply board: C201 and C202 (470 µF 16 V), C204 and C205 (2200 µF 16 V), C207 and C208 (4700 µF 16 V) and C210 and C211 (10 µF 16 V). The other two, C179 and C199 (10 µF 16 V), are on the motherboard. The CPU, ROM and RAM boards have none. The full list with packages and part numbers is on the Atari 800 Capacitor Replacement Guide.

Common failure points

Atari's symptom checklist (Section 6) is shared by the 400 and 800; it and the 800 flowcharts are reproduced on the Atari 800 Troubleshooting Guide. Points that matter for routine maintenance:

• A snowy screen is first the switch box, adaptor, channel switch, modulator adjustment or RF cable, before anything in the console.
• A green or yellow screen first means a faulty RAM module; Atari checks the lowest RAM slot first, then swaps the ROMs A401–A403.
• Some dead keys point at the keyboard; all keys dead point at POKEY (A101) and the multiplexers Z103 and Z104.
• Missing tones include C179, the radial electrolytic on the motherboard, among the possible causes.

Operating system ROMs

The same tip says to replace the ROMs if a printer overprints ("hiccups").

CTIA and GTIA

A301 on the CPU board is the video chip. Early machines have the CTIA (C012295) and later ones the GTIA (C014805). Atari's Upgrade Bulletin 1 describes the swap and says that software written for the GTIA's extra modes does not display correctly on a CTIA machine. Late-production 800s have a revised CPU board with Atari's SALLY 6502.

Lock-ups

Atari's Tech Tip 10 (22 February 1983) names dirty or corroded edge connectors and heat-related failure, particularly of the 6502, as the hardware causes of intermittent lock-ups, after ruling out BASIC editing and faulty software. Its test is a 12-hour burn-in on the SALT 2.05 continuous RAM test.

Diagnostics

The 400 and 800 have no built-in self-test. With no cartridge and no powered disk drive a working 800 starts in Memo Pad. Atari's field tests use the SALT II diagnostic cartridge in the left slot: colour bar, grey bar, keyboard, tone, console switch, ROM verify, RAM and port tests, each with a flowchart in section 7.

Recommended tools

See Recommended Tools. For this machine: a meter that reads AC volts for the adaptor, isopropyl alcohol and a contact lubricant for the board fingers, and a scope or frequency counter for the clock checks.

Maintenance checklist

1. Measure the adaptor on the AC range.
2. Check the interlock S201 and the power switch S202.
3. Remove the ROM and RAM modules and clean and lubricate their edge fingers.
4. Inspect the controller, peripheral and power jacks, the RF cable and the cartridge slots.
5. Look for domed or leaking electrolytics on the power supply board, and replace any that have failed (see Atari 800 Capacitor Replacement Guide).
6. Refit the ROM module in the slot nearest the keyboard.

Related pages

• Atari 800
• Atari 800 Capacitor Replacement Guide
• Atari 800 Troubleshooting Guide
• Atari 400 General Maintenance
• Recommended Tools