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Rebuild from Atari 400/800 Field Service Manual (hosted): every designator in the old tables was impossible (400 uses C1xx-C5xx blocks by board). Real list is 8 electrolytics - C192 on the motherboard and C201/202/204/205/207/209/210 on the PSU board. Added real rails (+5A/+5B/+12/-5), real regulators A201/A202, clock check points; cited throughout
 
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[[File:Atari 400 (photo).jpg|thumb|right|300px|Atari 400]]
The '''[[Atari 400]]''' is a four-board machine: a motherboard, a power supply PCB, a plug-in CPU card and a plug-in RAM card. '''Every aluminium electrolytic capacitor in the machine except one is on the power supply PCB''', and that board is also where the 9 V AC input is rectified and regulated. Everything else on the 400 is ceramic, mylar or polyester film and does not need replacing on age alone.


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The values below come from Atari's own parts list in the ''ATARI Home Computer Field Service Manual 400/800''.<ref name="fsm">Atari, Inc., ''ATARI Home Computer Field Service Manual 400/800'', June 1982, Section 9, "ATARI 400 Computer Console Parts List", pages 9-1 to 9-6. Hosted on this wiki: [[:File:Atari 400 800 Field Service Manual June 82.pdf]]. Source of every capacitor value, voltage rating, reference designator and Atari part number on this page.</ref>


'''Recapping your Atari 400 is a crucial preventative step to ensure reliable operation, stable power delivery, and crisp video output.''' 
== How the 400 is numbered ==
The original aluminium electrolytic capacitors in the Atari 400 are now over four decades old—well past their intended service life. Ageing capacitors can cause power instability, random crashes, distorted audio, and display artefacts. Proactive replacement restores system health and helps prevent catastrophic failures.


== 🔍 Visual Inspection & Failure Signs ==
Atari allocated a block of reference designators to each board, and this is the quickest way to tell whether a designator you have been given is even possible:<ref name="fsm" />
Before beginning, examine each capacitor for classic signs of failure:


* '''Bulging or domed tops''' – Indicates internal gas pressure and imminent failure.
{| class="wikitable styled-table" style="width:80%;"
* '''Leaking electrolyte''' – Brown, black, or green residue at the base or leads.
|+ Atari 400 reference designator blocks
* '''Corrosion or PCB staining''' – Green/white deposits or darkened board areas.
! Board !! Atari assembly number !! Designators
* '''Intermittent resets, video glitches, or audio hum''' – Often traceable to dried-out or high-ESR capacitors.
|-
| Motherboard || CA014807 || C101–C203, R101–R185, A101–A111, Z101–Z105
|-
| Power supply PCB || CA014155 || C201–C213, R201–R203, A201–A203, S201–S203, J201–J204
|-
| CPU card || CA017173 || C301–C307, R302–R313, A301–A303, Z301–Z304
|-
| RAM card || CA014801 (8K) / CA014802 (16K) || C501–C523, Z501–Z512
|}


If any single capacitor shows symptoms, it is best practice to replace '''all''' electrolytic capacitors on the mainboard.
A capacitor list for the 400 that quotes designators below C101 is not describing this machine.


== 📋 Atari 400 Capacitor List ==
== Visual inspection and failure signs ==


The Atari 400 uses a modest number of electrolytic capacitors, all of which are through-hole types on the mainboard and power supply board. SMD electrolytics are not present in this model.
* '''Bulging or domed tops''' — internal gas pressure and imminent failure.
* '''Leaking electrolyte''' — brown, black or green residue at the base or leads.
* '''Corrosion or board staining''' — green or white deposits, or darkened board around the leads.
* '''Random resets, video noise or audio hum''' — often traceable to dried-out or high-ESR capacitors on the supply board.


=== 🖥️ Mainboard Electrolytic Capacitors ===
See [[Capacitor Failure Symptoms]] for the general case, and [[Battery Explosion, Capacitor or Corrosion Damage]] if electrolyte has already reached the board.


{| class="wikitable styled-table" style="width:100%; text-align:center;"
== Capacitor list ==
|+'''Atari 400 Mainboard Electrolytic Capacitors'''
 
! Ref. Designator !! Capacitance !! Voltage !! Function / Notes
=== Power supply PCB (CA014155) ===
 
This board carries the mains-derived circuitry, both regulators, the RF modulator and the power and interlock switches. Seven of the machine's eight electrolytics are here.<ref name="fsm" />
 
{| class="wikitable styled-table" style="width:90%; text-align:center;"
|+ Atari 400 power supply PCB electrolytic capacitors
! Designator !! Value !! Rating !! Package !! Atari part number
|-
|-
| C44 || 2200 µF || 16 V || Main +5 V rail smoothing (bulk filter)
| C201 || 470 µF || 16 V || Axial || C014370
|-
|-
| C43 || 470 µF || 16 V || +12 V rail smoothing (video/audio circuits)
| C202 || 470 µF || 16 V || Axial || C014370
|-
|-
| C42 || 47 µF || 16 V || +5 V local decoupling (logic)
| C204 || 2200 µF || 16 V || Axial || C014373
|-
|-
| C41 || 10 µF || 16 V || +5 V local decoupling (logic)
| C205 || 2200 µF || 16 V || Axial || C014373
|-
|-
| C40 || 10 µF || 16 V || +5 V local decoupling (logic)
| C207 || 10 µF || 16 V || Axial || C014371
|-
|-
| C39 || 1 µF || 50 V || Video output coupling
| C209 || 4700 µF || 16 V || Radial || C014374-01 or C014374-02
|-
|-
| C38 || 1 µF || 50 V || Audio output coupling
| C210 || 22 µF || 16 V || Axial || C014393
|}
|}


''Note: Some board revisions may use slightly different reference numbers—always cross-check with your silkscreen before ordering.''
The remaining capacitors on this board are not electrolytics and should be left alone unless they test faulty: C203, C208 and C211 are 0.22 µF polyester film (C010394), C206 is 0.1 µF ceramic and C212–C213 are 0.001 µF ceramic.<ref name="fsm" />
 
=== Motherboard (CA014807) ===
 
{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+ Atari 400 motherboard electrolytic capacitors
! Designator !! Value !! Rating !! Package !! Atari part number
|-
| C192 || 10 µF || 16 V || Axial || C014371
|}
 
C192 is the only aluminium electrolytic on the 400 motherboard. Everything else in the C101–C203 range is ceramic (0.001 µF, 0.01 µF, 0.1 µF, or small NP0 values), mylar (C135–C142 and C181 at 0.047 µF) or polyester (C177–C178 at 820 pF).<ref name="fsm" />
 
=== CPU and RAM cards ===
 
'''Neither plug-in card contains an electrolytic capacitor.''' C301–C307 on the CPU card and C501–C523 on the RAM card are all ceramic axial types.<ref name="fsm" /> If someone has sold you a "400 cap kit" containing parts for these cards, it is not a 400 kit.
 
The Console5 Tech Wiki capacitor list for the 400 agrees with Atari's parts list exactly — the same eight designators at the same values.<ref name="c5">[https://wiki.console5.com/wiki/Atari_400 "Atari 400"], Console5 Tech Wiki, retrieved September 2026. Secondary source; its capacitor list matches Atari's own parts list designator for designator, and it additionally identifies A201 as a 7812 and A202 as a 7805.</ref>
 
== What the rails actually are ==


=== 🔌 Internal Power Supply Board ===
Atari is explicit about this, and it matters because it tells you what each capacitor is working against:


If your Atari 400 has the original internal linear power supply (NTSC models), it contains additional electrolytic capacitors:
<blockquote>"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="fsm2">Atari, Inc., ''ATARI Home Computer Field Service Manual 400/800'', June 1982, page 1-6, "Power Supply". Source of the 9 V AC input figure and the four-rail breakdown.</ref></blockquote>


{| class="wikitable styled-table" style="width:80%; text-align:center;"
{| class="wikitable styled-table" style="width:80%;"
|+'''Atari 400 Power Supply Board Electrolytic Capacitors'''
|+ Atari 400 supply rails
! Ref. Designator !! Capacitance !! Voltage !! Function
! Rail !! Purpose
|-
| +5 V A || Supply voltage for the logic PCBs
|-
| +5 V B || Specially filtered supply for the video circuitry
|-
|-
| C1 || 4700 µF || 16 V || Main input filter (rectified DC)
| +12 V || Supply for the dynamic RAM chips (and SIO pin 12)
|-
|-
| C2 || 1000 µF || 16 V || +12 V rail filter
| −5 V || Supply for the dynamic RAM chips
|}
|}


''PAL models (with external power bricks) may not have these internal capacitors. Always inspect your specific unit.''
The 16K RAM card is populated with eight DRAMs at Z505–Z512 that need all three of +12 V, +5 V and −5 V; that is why the 400 has rails an XL-series machine does not.<ref name="fsm" />


== 🛠️ Recapping Procedure ==
The regulators are '''A202 (5 V)''' and '''A201 (12 V)''' on the power supply PCB.<ref name="fsm" /> Console5 identifies these as a 7805 and a 7812 respectively.<ref name="c5" />


# '''Power off and unplug''' the Atari 400. Wait several minutes for capacitors to discharge.
== Recapping procedure ==
# '''Disassemble''' the case: remove screws from the underside, gently separate the top shell, and disconnect the keyboard membrane.
# '''Remove the mainboard''' and, if present, the internal power supply board.
# '''Label all connectors''' for easy reassembly.
# '''Desolder each capacitor''' using a soldering iron (350–375 °C) and wick or pump. Take care not to lift PCB pads.
# '''Clean the pads''' with isopropyl alcohol and inspect for damage.
# '''Install new capacitors''', matching '''polarity''' (long lead = positive) and ensuring correct lead spacing.
# '''Trim excess leads''', solder cleanly, and inspect for bridges or cold joints.
# '''Reassemble''' the unit, reconnecting all cables and the keyboard membrane.


== 🧰 Recommended Tools & Parts ==
{{Warning|The power supply PCB is fed from a transformer, but its ON/OFF switch (S203) opens the '''9 V AC''' input, and the board carries that AC as far as the rectifier diodes CR206–CR209. Unplug the adaptor at the wall before working on the board, and remember that C209 (4700 µF) can hold a charge after power-off — discharge it through a resistor before touching the board.}}


* Temperature-controlled soldering iron (2 mm chisel tip recommended)
# Unplug the adaptor and all peripherals.
* Desoldering braid and/or spring pump
# Open the case and lift out the power supply PCB. Note that the '''power interlock switch S202''' is on this board; it cuts power when the cartridge cover is lifted, so the machine will appear dead on the bench with the lid off.<ref name="fsm" />
* Leaded 63/37 or quality lead-free solder (0.5–0.7 mm)
# Photograph and label every connector before disconnecting: J201 (20-pin socket to the motherboard), J202 (13-pin SIO), J203 (phono) and J204 (power jack).
* Isopropyl alcohol (99%) and antistatic brush
# Desolder each capacitor with braid or a pump. Take care with the pads around C209 — it is the largest can and its pads carry the full rectified current.
* Side-cutters for trimming leads
# Clean the pads with isopropyl alcohol and check for lifted traces, particularly if electrolyte has already leaked.
* Multimeter (for continuity and voltage checks)
# Fit the new capacitors observing '''polarity'''. A higher voltage rating than the original is always acceptable; a lower one never is.
* '''105 °C, low-ESR''' radial electrolytic capacitors (brands: Nichicon, Panasonic, Rubycon)
# Reassemble, then verify the rails before fitting the cards back (see below).
* Kapton tape (optional, for insulating capacitors near shielding)


== ⚙️ Voltage & Ripple Check ==
== Recommended parts ==


After recapping and reassembly, verify the power rails at the mainboard edge connector or test points:
* 105 °C radial aluminium electrolytics from a reputable manufacturer (Nichicon, Panasonic, Rubycon).
* C209 is the only radial part in the original design; the rest are axials. Radial replacements are fine electrically but need their leads dressed to reach axial pads.
* See [[Recommended Tools]] for soldering and desoldering equipment.


{| class="wikitable styled-table" style="width:70%; text-align:center;"
== Verifying the result ==
|+'''Atari 400 Power Rails (No Cartridge, BASIC READY)'''
 
! Test Point !! Expected Voltage !! Max Ripple (p-p)
Measure the rails with the machine assembled and running. Atari does not publish a tolerance band for the 400's internal rails, so treat the regulator types as the specification: a healthy 7805 and 7812 sit within a few per cent of nominal, and anything more than about 5 % off, or any visible ripple on a scope, means the job is not finished.
 
A more useful go/no-go check is the clock, which Atari ''does'' specify. With a scope, the following should be present:<ref name="fsmclock">Atari, Inc., ''ATARI Home Computer Field Service Manual 400/800'', June 1982, Table 5-1, "Clock Circuit", page 5-36. Frequencies and pin numbers for the 400/800 clock chain.</ref>
 
{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+ Clock check points (Atari Table 5-1)
! Point !! Board !! Frequency (MHz)
|-
| Pin 21 of J101 || CPU card || 1.789
|-
| Pin 9 of Z302 || CPU card || 1.789
|-
| Pin 35 of A302 (ANTIC) || CPU card || 3.579
|-
| Pin 29 of A301 (GTIA) || CPU card || 3.579
|-
| Collector of Q104 || Motherboard || 3.579
|-
|-
| +5 V (logic) || 4.90 – 5.10 V || < 50 mV
| Pin 7 of A101 (POKEY) || Motherboard || 1.789
|-
|-
| +12 V (video/audio) || 11.5 – 12.5 V || < 100 mV
| Pin 25 of A102 (PIA) || Motherboard || 1.789
|}
|}


* Use an oscilloscope (20 MHz bandwidth) to check ripple if available.
If the clock is right and the rails are right, a machine that still fails is not a capacitor problem — work through [[Atari 400 Troubleshooting Guide]] instead.
* Excessive ripple or unstable voltages may indicate a faulty power supply or incorrect capacitor installation.


== 💡 Additional Tips ==
== Related pages ==
* [[Atari 400]]
* [[Atari 400 General Maintenance]]
* [[Atari 400 Troubleshooting Guide]]
* [[Capacitor Failure Symptoms]]
* [[Recommended Tools]]


* '''Double-check polarity''' before soldering—reverse installation can damage the board.
== References ==
* Use capacitors with equal or higher voltage ratings; never substitute lower-voltage parts.
<references />
* Clean any electrolyte residue thoroughly to prevent corrosion.
* If the video output remains noisy after recapping, check the RF modulator and its internal capacitors (if fitted).
* Store the Atari 400 in a dry environment and power it up periodically to keep capacitors healthy.
* Dispose of old capacitors at an approved electronics recycling centre.


== 🔗 Related Pages ==
* [[Atari 400 Troubleshooting Guide]]
* [[Atari 400 Capacitor Replacement Guide]]
* [[Atari 400 Power Supply Maintenance]]
[[Category:Atari Systems]]
[[Category:Atari Systems]]
[[Category:Capacitor Replacement Guides]]
[[Category:Capacitor Replacement Guides]]
{{Navbox-AtariVintageComputers|state=collapsed}}

Latest revision as of 22:19, 22 September 2026

Atari 400

The Atari 400 is a four-board machine: a motherboard, a power supply PCB, a plug-in CPU card and a plug-in RAM card. Every aluminium electrolytic capacitor in the machine except one is on the power supply PCB, and that board is also where the 9 V AC input is rectified and regulated. Everything else on the 400 is ceramic, mylar or polyester film and does not need replacing on age alone.

The values below come from Atari's own parts list in the ATARI Home Computer Field Service Manual 400/800.[1]

How the 400 is numbered

[edit | edit source]

Atari allocated a block of reference designators to each board, and this is the quickest way to tell whether a designator you have been given is even possible:[1]

Atari 400 reference designator blocks
Board Atari assembly number Designators
Motherboard CA014807 C101–C203, R101–R185, A101–A111, Z101–Z105
Power supply PCB CA014155 C201–C213, R201–R203, A201–A203, S201–S203, J201–J204
CPU card CA017173 C301–C307, R302–R313, A301–A303, Z301–Z304
RAM card CA014801 (8K) / CA014802 (16K) C501–C523, Z501–Z512

A capacitor list for the 400 that quotes designators below C101 is not describing this machine.

Visual inspection and failure signs

[edit | edit source]
  • Bulging or domed tops — internal gas pressure and imminent failure.
  • Leaking electrolyte — brown, black or green residue at the base or leads.
  • Corrosion or board staining — green or white deposits, or darkened board around the leads.
  • Random resets, video noise or audio hum — often traceable to dried-out or high-ESR capacitors on the supply board.

See Capacitor Failure Symptoms for the general case, and Battery Explosion, Capacitor or Corrosion Damage if electrolyte has already reached the board.

Capacitor list

[edit | edit source]

Power supply PCB (CA014155)

[edit | edit source]

This board carries the mains-derived circuitry, both regulators, the RF modulator and the power and interlock switches. Seven of the machine's eight electrolytics are here.[1]

Atari 400 power supply PCB electrolytic capacitors
Designator Value Rating Package Atari part number
C201 470 µF 16 V Axial C014370
C202 470 µF 16 V Axial C014370
C204 2200 µF 16 V Axial C014373
C205 2200 µF 16 V Axial C014373
C207 10 µF 16 V Axial C014371
C209 4700 µF 16 V Radial C014374-01 or C014374-02
C210 22 µF 16 V Axial C014393

The remaining capacitors on this board are not electrolytics and should be left alone unless they test faulty: C203, C208 and C211 are 0.22 µF polyester film (C010394), C206 is 0.1 µF ceramic and C212–C213 are 0.001 µF ceramic.[1]

Motherboard (CA014807)

[edit | edit source]
Atari 400 motherboard electrolytic capacitors
Designator Value Rating Package Atari part number
C192 10 µF 16 V Axial C014371

C192 is the only aluminium electrolytic on the 400 motherboard. Everything else in the C101–C203 range is ceramic (0.001 µF, 0.01 µF, 0.1 µF, or small NP0 values), mylar (C135–C142 and C181 at 0.047 µF) or polyester (C177–C178 at 820 pF).[1]

CPU and RAM cards

[edit | edit source]

Neither plug-in card contains an electrolytic capacitor. C301–C307 on the CPU card and C501–C523 on the RAM card are all ceramic axial types.[1] If someone has sold you a "400 cap kit" containing parts for these cards, it is not a 400 kit.

The Console5 Tech Wiki capacitor list for the 400 agrees with Atari's parts list exactly — the same eight designators at the same values.[2]

What the rails actually are

[edit | edit source]

Atari is explicit about this, and it matters because it tells you what each capacitor is working against:

"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 400 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

The 16K RAM card is populated with eight DRAMs at Z505–Z512 that need all three of +12 V, +5 V and −5 V; that is why the 400 has rails an XL-series machine does not.[1]

The regulators are A202 (5 V) and A201 (12 V) on the power supply PCB.[1] Console5 identifies these as a 7805 and a 7812 respectively.[2]

Recapping procedure

[edit | edit source]
  1. Unplug the adaptor and all peripherals.
  2. Open the case and lift out the power supply PCB. Note that the power interlock switch S202 is on this board; it cuts power when the cartridge cover is lifted, so the machine will appear dead on the bench with the lid off.[1]
  3. Photograph and label every connector before disconnecting: J201 (20-pin socket to the motherboard), J202 (13-pin SIO), J203 (phono) and J204 (power jack).
  4. Desolder each capacitor with braid or a pump. Take care with the pads around C209 — it is the largest can and its pads carry the full rectified current.
  5. Clean the pads with isopropyl alcohol and check for lifted traces, particularly if electrolyte has already leaked.
  6. Fit the new capacitors observing polarity. A higher voltage rating than the original is always acceptable; a lower one never is.
  7. Reassemble, then verify the rails before fitting the cards back (see below).
[edit | edit source]
  • 105 °C radial aluminium electrolytics from a reputable manufacturer (Nichicon, Panasonic, Rubycon).
  • C209 is the only radial part in the original design; the rest are axials. Radial replacements are fine electrically but need their leads dressed to reach axial pads.
  • See Recommended Tools for soldering and desoldering equipment.

Verifying the result

[edit | edit source]

Measure the rails with the machine assembled and running. Atari does not publish a tolerance band for the 400's internal rails, so treat the regulator types as the specification: a healthy 7805 and 7812 sit within a few per cent of nominal, and anything more than about 5 % off, or any visible ripple on a scope, means the job is not finished.

A more useful go/no-go check is the clock, which Atari does specify. With a scope, the following should be present:[4]

Clock check points (Atari Table 5-1)
Point Board Frequency (MHz)
Pin 21 of J101 CPU card 1.789
Pin 9 of Z302 CPU card 1.789
Pin 35 of A302 (ANTIC) CPU card 3.579
Pin 29 of A301 (GTIA) CPU card 3.579
Collector of Q104 Motherboard 3.579
Pin 7 of A101 (POKEY) Motherboard 1.789
Pin 25 of A102 (PIA) Motherboard 1.789

If the clock is right and the rails are right, a machine that still fails is not a capacitor problem — work through Atari 400 Troubleshooting Guide instead.

[edit | edit source]

References

[edit | edit source]
  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, Section 9, "ATARI 400 Computer Console Parts List", pages 9-1 to 9-6. Hosted on this wiki: File:Atari 400 800 Field Service Manual June 82.pdf. Source of every capacitor value, voltage rating, reference designator and Atari part number on this page.
  2. ↑ 2.0 2.1 "Atari 400", Console5 Tech Wiki, retrieved September 2026. Secondary source; its capacitor list matches Atari's own parts list designator for designator, and it additionally identifies A201 as a 7812 and A202 as a 7805.
  3. ↑ Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, page 1-6, "Power Supply". Source of the 9 V AC input figure and the four-rail breakdown.
  4. ↑ Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982, Table 5-1, "Clock Circuit", page 5-36. Frequencies and pin numbers for the 400/800 clock chain.



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