Atari 800 Capacitor Replacement Guide
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The Atari 800 has five kinds of circuit board: the motherboard, the power supply board, a plug-in CPU board, a plug-in ROM personality module and one to three plug-in RAM modules. It has ten aluminium electrolytic capacitors, eight of them on the power supply board, which rectifies and regulates the 9 V AC from the external adaptor. The CPU, ROM and RAM boards have no electrolytics.
The values below are from Atari's parts list in the ATARI Home Computer Field Service Manual 400/800.[1]
Designators
[edit | edit source]Atari numbers each board in its own block:[1]
| Board | Atari assembly or board number | Designators |
|---|---|---|
| Motherboard | CA014829 (bare board) | C101–C200, R101–R206, A101–A104, Z101–Z106, Q101–Q107 |
| Power supply board | CA014171 | C201–C216, R201–R204, A201–A203, CR201–CR211, S201–S207, J201–J206 |
| CPU board | CA017173 | C301–C307, R302–R313, A301–A303, Z301–Z304 |
| ROM personality module | CA014090-01 (board CA014803) | C401–C411, R401–R404, A401–A403, Z401–Z403 |
| RAM module, 16 KB | CA014802 | C501–C523, Z501–Z512 |
The motherboard's resistor numbers run past R200, so R201–R204 appear in both the motherboard and power supply lists as different parts. Check which board a list refers to before ordering.[1]
Visual inspection
[edit | edit source]Look for domed tops, electrolyte residue at the base or leads, and staining of the board around the leads. See Capacitor Failure Symptoms for the general case, and Battery Explosion, Capacitor or Corrosion Damage if electrolyte has reached the board.
Before replacing anything, measure the adaptor on the AC range, check the interlock switch S201 with the cartridge door shut, and measure the three rails at J201 as described under Checks after the recap. Atari's flowcharts name the power supply electrolytics only once a rail is missing.[2] On his Atari Projects site Jason Moore reports that the original electrolytics in Atari 8-bit computers do not fail often, though some do.[3]
Capacitor list
[edit | edit source]Power supply board (CA014171)
[edit | edit source]This board carries the bridge rectifier, both regulators, the RF modulator, the monitor and SIO jacks, the power and interlock switches and the four console keys.[1][4]
| Designator | Value | Rating | Package | Atari part number | Circuit (Figure 2-8) |
|---|---|---|---|---|---|
| C201, C202 | 470 µF | 16 V | Axial | C014370 | −5 V supply |
| C204, C205 | 2200 µF | 16 V | Axial | C014373 | +12 V voltage doubler |
| C207, C208 | 4700 µF | 16 V | Radial | C014374-01 or -02 | Reservoir after the bridge rectifier, ahead of the 7805 |
| C210 | 10 µF | 16 V | Axial | C014371 | +5 V B (video) filter |
| C211 | 10 µF | 16 V | Axial | C014371 | SIO motor control line (J204 pin 8) |
The Console5 TechWiki list, headed "Power Supply, REV B", gives C207 and C208 as 25 V and agrees with Atari on the other positions.[5] Read what is printed on the parts in your machine; a 25 V part fits either way.
The other capacitors on this board are C203 and C206 (0.22 µF 100 V poly film, C010394), C215 across the AC input (0.47 µF 100 V mylar, 21-101474M), C209 (0.1 µF ceramic), C212 and C216 (0.001 µF ceramic) and C214 (10 pF ceramic).[1][4]
Motherboard
[edit | edit source]| Designator | Value | Rating | Package | Atari part number |
|---|---|---|---|---|
| C179 | 10 µF | 16 V | Radial | C014392 |
| C199 | 10 µF | 16 V | Axial | C014371 |
These are the only electrolytics on the motherboard.[1] C179 is one of the parts Atari's symptom checklist lists for "tones missing during sound or games".[6]
The rest are ceramics, 0.22 µF 100 V poly film at C103 and C180 (C010394), 0.047 µF 100 V mylar at C127–C134 (21-101473, with a ceramic alternative), and two 820 pF 50 V capacitors at C169 and C173 (C010821, the part number Atari's 2600 parts list gives for its 820 pF polystyrene capacitors).[1][7] On the 800, C177 and C178 are 0.001 µF ceramics; the 820 pF parts at C177 and C178 are on the 400 motherboard.[1]
CPU board, ROM module and RAM modules
[edit | edit source]None of the plug-in boards has an electrolytic. C301–C307, C401–C411 and C501–C523 are ceramic axial parts: 0.001 µF, 0.01 µF and 0.1 µF decoupling, plus 47 pF and 68 pF on the ROM module and 47 pF on the RAM module.[1]
Supply rails
[edit | edit source]Atari's description: "The Power Supply PCB receives 9VAC from an external power adaptor (transformer) and provides +5Vdc, +12Vdc, and -5Vdc for the Console system."[8]
| Rail | J201 pin | Use (Atari p. 1-6) | Source (Figure 2-8) |
|---|---|---|---|
| +5 V A | 18, 19 | Logic boards | A202, drawn as a 7805 (Atari C014348), with R203 (33 Ω 2 W) across it |
| +5 V B | 17 | Video circuitry, specially filtered | +5 V A through L201, with C209 and C210 |
| +12 V | 21 | Dynamic RAM, and SIO pin 12 | Doubler CR204/CR205 with C204/C205, then A201, printed 78M12 (Atari C014349) |
| −5 V | 1 | Dynamic RAM | CR202/CR203 with C201/C202, zener CR201 (1N5231B); the power LEDs CR210 and CR211 are in this circuit |
The 9 V is AC from the adaptor (Atari C014319). The bridge is CR206–CR209 (MR501), and the regulators sit on heatsink assembly CA014708.[1][4]
Recapping procedure
[edit | edit source]Atari's disassembly order, from section 4 of the manual:[9]
- Switch off and unplug the adaptor and all peripherals.
- 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.
- Turn the console upside down, remove the five bottom-cover screws and tilt the bottom cover off.
- Remove the two screws in the aluminium casting flange and the single screw at the lower left corner of the power supply board. Disconnect and set aside the speaker.
- Turn the console over, tilt the top cover back to 90°, unplug the keyboard ribbon and set the top cover aside.
- Lift the power supply board straight up. Unplug the RF cable and the power supply harness and remove the board's three screws.
- Desolder each capacitor with braid or a pump, clean the pads with isopropyl alcohol and check for lifted traces.
- Fit the new capacitors with the correct polarity. A higher voltage rating than the original is acceptable; a lower one is not.
- Reassemble in reverse order. Atari's torque limits are 6 inch-pounds into plastic and 10 inch-pounds into aluminium, and screws of different sizes are not interchangeable.[9] The ROM module goes in the slot nearest the keyboard.[10]
C179 and C199 are on the motherboard, which comes out after the nine screws of the lower shield and four nylon clips (pp. 4-12 and 4-13); pry the clips carefully so as not to bend the motherboard connector pins.[9]
C207 and C208 are the only radial parts on the power supply board; the other electrolytics there are axial. Radial replacements work in axial positions if their leads are dressed to reach the pads. See Recommended Tools for soldering and desoldering equipment.
Checks after the recap
[edit | edit source]Atari's 800 power-up flowcharts check for +5 V at J201 pin 17, −5 V at J201 pin 1 and +12 V at J201 pin 21. With +5 V missing they point at the bridge diodes CR206–CR209 (and say to replace 1N4001-type diodes there with 1N5391, C017988), A202, C208, C209, R203 and the power switch S202. On the 800, C209 is the 0.1 µF ceramic and C207 is the second 4700 µF reservoir, in parallel with C208, so check C207 as well. With +12 V missing they point at A201, CR204 and C203–C205. The box for missing −5 V prints the same +12 V parts (CR204, CR205, C203–C205, C212); on the schematic the −5 V supply is CR201–CR203 with C201 and C202.[2][4] Atari gives no tolerance band for these rails.
With a scope, the clock should be present at these points:[2]
| Point | Board | Frequency (MHz) |
|---|---|---|
| Pins 21 and 22 of J101 | CPU board | 1.789 |
| Pins 8, 9, 10 and 13 of Z302 | CPU board | 1.789 |
| Pin 37 of A303 | CPU board | 1.140 (as printed) |
| Pin 6 of Z301 | CPU board | 1.789 |
| Pin 34 of A302 (ANTIC) | CPU board | 1.789 |
| Pin 35 of A302 (ANTIC) | CPU board | 3.579 |
| Pins 28 and 29 of A301 (GTIA) | CPU board | 3.579 |
| Collector of Q102 | Motherboard | 3.579 |
| Pin 7 of A101 (POKEY) | Motherboard | 1.789 |
| Pin 25 of A102 (PIA) | Motherboard | 1.789 |
If the clock and the rails are right and the machine still fails, see the Atari 800 Troubleshooting Guide.
Related pages
[edit | edit source]- Atari 800
- Atari 800 General Maintenance
- Atari 800 Troubleshooting Guide
- Atari 400 Capacitor Replacement Guide
- Capacitor Failure Symptoms
- Recommended Tools
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, Section 9, "ATARI 800 Computer Console Parts List", pp. 9-7 to 9-13. Hosted here as Atari 400/800 Field Service Manual (PDF). Source of every capacitor value, voltage rating, designator and Atari part number below.
- ↑ 2.0 2.1 2.2 Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, Section 7, "800 Power-Up" flowcharts AA (snowy screen, p. 7-3) and BB (black/grey screen, p. 7-4), and Table 7-1 "Clock Circuit", p. 7-36.
- ↑ Jason H. Moore, "Replace Faulty Capacitors on Your Atari 8-Bit Computer Circuit Board", Atari Projects, 6 October 2024: the capacitors in 1970s and early-1980s Atari 8-bit computers "don't seem to fail too often".
- ↑ 4.0 4.1 4.2 4.3 Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, Figure 2-8, "800 Power Supply Schematic", p. 2-13.
- ↑ Console5 TechWiki, "Atari 800", capacitor list. Community kit list, not an Atari document.
- ↑ Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, Section 6, "Symptom Checklist", pp. 6-1 and 6-2.
- ↑ Atari, Inc., Video Computer System Field Service Manual, Domestic Model 2600/2600A, Section 8 parts lists: C010821, "Cap. Polystyrene 820pF (50V)". Hosted here as Atari 2600 and 2600A Field Service Manual.
- ↑ Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, p. 1-6, "Power Supply".
- ↑ 9.0 9.1 9.2 Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, Section 4, "ATARI 800 Home Computer Console – Disassembly", pp. 4-8 to 4-14, and the notes on p. 4-1.
- ↑ Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, "RAM and ROM Module Installation", p. 4-20.