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Atari 2600 Jr Power Supply Circuit Repair

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Atari 2600 Jr motherboard power section (C26, S4, VR1)
The power section at the left end of an NTSC 2600 Jr. board: the reservoir C26 (blue, upper left), the power switch S4, the trimmer R9, C36, C37, R57, the red LED DS1 and the regulator VR1 (UA7805UC) screwed to its tinned pad (photo: Evan-Amos, public domain)

The Atari 2600 Jr runs from an external adaptor and makes its own +5 V with a 7805 regulator, VR1, on the main board.[1][2] retro64 describes the 2600's adaptor as a 9 V DC unregulated type, which leaves the regulator on the board to drop the voltage to 5 V for the chips.[3] When the supply path fails the console gives no picture, often with the power LED still lit, or the picture comes and goes. Atari's 2600 field service manual covers only the CX2600 and CX2600A, so the designators below come from Jerzy Sobola's redrawn schematic of a PAL Jr. board; the photographed NTSC board carries the same designators for every part in the power section.[4][1][2] For the six-switch and four-switch consoles see Atari 2600 Power Supply Circuit Repair.

Atari 2600 Jr PAL schematic, power input and regulator (Jerzy Sobola)
The power input on the PAL schematic: J2, C2, the 2200 µF reservoir C26, the power switch S4, C37, the 7805 VR1 and C36. R57 and the LED DS1 take their feed from the switched side of S4, ahead of the regulator (drawing: Jerzy Sobola)

The power path on the PAL schematic:[1]

2600 Jr. power path (PAL schematic)
Part Value or type Position
J2 Power input jack Adaptor input, at the rear edge of the board
C2 0.1 µF Across the input
C26 2200 µF Reservoir, ahead of the power switch
S4 Slide switch Power switch
C37 4.7 µF Regulator input, after the switch
VR1 7805 +5 V regulator (VCC)
C36 0.1 µF Regulator output
R57, DS1 750 Ω, LED Power LED, fed from the switched input ahead of VR1

Symptoms

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  • LED on, no picture: retro64's Jr. lit its power LED at full brightness but showed no picture; the supply on the chips was below 1 V and the 7805 was putting out the same low voltage. A new 7805 brought the picture back.[3] On the Jr. the LED runs from the unregulated supply, so it lights whether or not the regulator works.[3][1]
  • LED off, no picture: power is not getting through the switch. Check the adaptor, the jack J2 and the switch S4. If VR1's output is +5 V and only the LED is dark, check R57 and DS1.[1]
  • Flaky operation or a flashing screen: on the 2600 Dave Farquhar puts this down to a dirty or oxidised power switch.[5]
  • The regulator runs hot or the fault comes and goes: TBA has found Jr. consoles with nothing holding the regulator to its cooling pad.[6]

If VR1 gives a steady 5 V and the screen is still black or snowy, the fault is elsewhere; see the Atari 2600 Jr Troubleshooting Guide.

Safety

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  • The work is at low voltage; on the 2600 Farquhar expects no more than 15 V DC inside the console.[7]
  • C26 sits on the adaptor side of S4, so it can stay charged with the switch off.[1] On the 2600 Farquhar discharges the large reservoir by unplugging the adaptor, switching on and leaving the console for about five minutes, and otherwise keeps his fingers off its leads.[5]
  • The 6507, 6532 and TIA are sensitive to static; Atari asks technicians to wear a grounding strap when working on the 2600.[8]

Tools and parts

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  • A multimeter and a known-good adaptor. Farquhar expects a working original 2600 adaptor to read more than 9 V across its plug with no load, and a newer one may read 9 V.[5] The owner's leaflet warns that an adaptor not designed for the 2600 can damage the console.[9]
  • A new 7805 regulator in a TO-220 package; the photographed board has a UA7805UC at VR1.[2] Use a new part: retro64 first fitted a 7805 taken from a Commodore 64 board and it gave about 6 V on the original Atari adaptor until it was replaced with a new one.[3]
  • Heatsink compound and isopropyl alcohol.[7]
  • A screw and nut to hold the regulator to its pad if the board has none.[6]
  • Contact cleaner for the power switch.[5]
  • A soldering iron (Farquhar uses a 25 W iron), solder, flux and a desoldering tool.[5][7]

Procedure

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Opening the case

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Atari 2600 Jr with top case removed
With the top case off, the power section at the left end of the board sits outside the RF shield (photo: Evan-Amos, public domain)

TBA's manual warns that the Jr. case is brittle and that its internal screw posts and the board's snap levers break easily.[6]

  1. Unplug the adaptor and the RF cable. Turn the console over and remove the screws from the underside; R3UK's UK PAL Jr. had five.[10]
  2. Lift the left side of the top case first. The SELECT and RESET buttons are joined to the board by a flexible cable; pull it carefully out of its connector, then lift the top case away.[6][10]
  3. For the voltage checks the board can stay in the lower case: C26, S4, DS1 and VR1 are at the left end of the board, outside the RF shield.[11]
  4. To replace a part, release the snap levers on the left and right edges and lift the board out.[6]

Following the supply

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Atari 2600 and 2600A IC pinouts (FSM figure 2-1)
Atari's pinout for the 2600 regulator: in, ground, out (field service manual figure 2-1)

The 7805's pins are input (1), ground (2) and output (3).[12] Atari's drawing for the 2600 shows them in that order from the left, with the printed face towards you and the tab at the top.[13] On the Jr. the regulator lies flat with its legs pointing towards the LED, and the tinned area round it is ground.[2][10]

  1. Plug in a known-good adaptor and switch on. Put the meter's black lead on the regulator's fixing screw. Farquhar uses the screw, which is grounded, to avoid shorting the centre pin.[5] If there is no screw, use the tinned area round the regulator, which R3UK notes is ground.[10]
  2. Measure VR1's output pin, which connects to VCC and C36.[1] A 7805 is specified to give 4.75 to 5.25 V across its load and temperature range.[12] If the output is in range, the supply is good; go back to the Atari 2600 Jr Troubleshooting Guide.
  3. If the output is low or missing, measure VR1's input pin. On the 2600 Farquhar expects about 9 V there; TI gives 7.5 V as the lowest input that keeps a 7805 in regulation.[5][12]
  4. If the input is good and the output is not, the regulator is faulty. Farquhar treats a 2600 regulator whose output is more than about 0.15 V from 5 V as bad.[7] Atari's flowchart for the CX2600A also includes a check of the +5 V line for a short to ground.[14]
  5. If the input is missing, measure on both sides of S4 with the switch on. Voltage on one side only means the switch is open.[7][1]
  6. If neither side of S4 has voltage, measure across C26 and then at J2. No voltage at J2 with the adaptor plugged in points to the adaptor or the jack.[1][5]

Cleaning the power switch

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Atari 2600 Jr motherboard power jack J2
The power jack J2 at the rear edge of an NTSC Jr. board (photo: Evan-Amos, public domain)

Farquhar's method for the 2600's switches:[5]

  1. With the power off, work the switch back and forth about 100 times.
  2. If that does not cure it, spray a plastic-safe contact cleaner into the opening in the side of the switch and work it again.
  3. Leave it to dry for 30 minutes before powering up.

S4 on the photographed board is marked C020480-02; S5 beside it carries the same marking.[2]

Reflowing the power jack

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  1. With the board out, turn it over and find the joints under J2.[1][2]
  2. Reflow any that are dull or cracked, adding a little fresh solder. The finished joints should be shiny and unbroken, and the jack should not move when pushed by hand.[5]

Replacing the regulator

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Farquhar's method on the 2600, with TBA's note for Jr. boards that have no fixing:[7][6]

  1. Unplug the adaptor and take the board out. Remove the screw and nut that hold VR1 to its pad, if there are any, and keep them.[7][2]
  2. Bend the regulator straight up and cut its legs close to the body, leaving enough of each leg to grip.[7]
  3. Heat each joint from the underside and pull the leg out with pliers as the solder melts. Clear the holes.[7]
  4. Clean the old heatsink compound off the pad with isopropyl alcohol and put a small dab of fresh compound where the old compound was.[7]
  5. Fit the new regulator the same way round as the old one, bend it down onto the pad and fit the screw.[7] If the board had nothing holding the regulator, TBA advises fitting a screw through the board or soldering the tab to the pad.[6]
  6. Solder the three legs from the underside, using flux so that each joint takes less than about ten seconds, then clean the joints with isopropyl alcohol.[7]

Reassembly

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  1. Refit the board in the lower case so that the snap levers hold it.[6]
  2. Plug the SELECT and RESET flex cable back into its connector before closing the case.[6][10]
  3. Refit the top case and the screws with care; TBA warns that the screw posts snap easily.[6]

Testing

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  • With a game running, VR1's output should read between 4.75 and 5.25 V.[12] Check it on the adaptor you will use: retro64's second-hand 7805 gave 5 V on a home-built supply but about 6 V on the original Atari adaptor.[3]
  • retro64 recommends a regulated switching adaptor for the 2600, to put less stress on the 7805, and uses one rated at 1 A.[3]
  • With a game running, the picture should stay steady. On the 2600 Farquhar links intermittent power to cracked joints on the power jack and a flashing screen to a dirty power switch.[5]
  • Atari's procedures for the 2600 end every repair with a burn-in of at least two hours.[8]

Board variations

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  • The schematic is of a PAL board ("Motherboard C012283 rev. B"); the photographed board is NTSC. Both use J2, C26, S4, C37, VR1, C36, R57 and DS1 for the power section.[1][2]
  • The photographed NTSC board has VR1 held by a screw and nut.[2] TBA has seen Jr. boards with no fixing at all.[6]
  • TBA's manual mentions a rare "one-chip" Jr. board; it may not follow this layout.[6]
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References

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  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Jerzy Sobola, redrawn schematic "Motherboard C012283 rev. B, Atari 2600 Game Console", sheet 1 of 2, 8 September 2000 (PAL 2600 Jr.): J2, C2, C26, S4, C37, VR1, C36, R57 and DS1. Hosted here as File:Atari 2600 Jr PAL motherboard schematic (Jerzy Sobola).png.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Evan-Amos, photograph of an NTSC Atari 2600 Jr. motherboard, Wikimedia Commons, public domain; designators and markings read from the image. Hosted here as File:Atari-2600-Jr-Motherboard-Flat.jpg.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 retro64, "Atari 2600 and 7800: repair tales": a 2600 Jr. with the LED lit, no picture and less than 1 V on the chips; the LED on the unregulated supply; a used 7805 that gave about 6 V on the original adaptor; the 9 V unregulated adaptor and the 1 A regulated replacement.
  4. ↑ Atari, Inc., Video Computer System Field Service Manual, Domestic Model 2600/2600A, FD100133 Rev. 02. It does not cover the 2600 Jr. Hosted here as Atari 2600 and 2600A Field Service Manual.
  5. ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 Dave Farquhar, "Atari 2600 won't turn on? Try this.", The Silicon Underground, 26 June 2019, updated 19 January 2025: the large capacitor and how he discharges it, adaptor voltages, switch cleaning, reflowing the power jack, and measuring the 7805 with the black lead on its screw.
  6. ↑ 6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 6.11 The Brewing Academy, Bryan's Ultimate Atari Video Rev. D Instruction Manual, revision 1.94, "Atari 2600 Jr." (p. 12): the brittle case, the flex cable, the snap levers, the regulator pad, and the one-chip board. PDF from thebrewingacademy.com.
  7. ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 7.11 Dave Farquhar, "Atari 2600 voltage regulator troubleshooting and replacement", The Silicon Underground, 23 March 2020, updated 19 January 2025: voltage on both sides of the switch, readings within about 0.15 V of 5 V, and his replacement method.
  8. ↑ 8.0 8.1 Atari, Field Service Manual FD100133 Rev. 02, Section 4 introduction, p. 4-1: burn-in for at least two hours after every repair; the LSI chips' sensitivity to static and the grounding strap.
  9. ↑ Atari Corp., Atari 2600 owner's leaflet for the 2600 Jr., C026260-001, 1986: use only the AC power adaptor designed for the 2600. Hosted here as File:Atari 2600 Jr Owner's Manual C026260-001.pdf.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 David Savery, "Atari 2600 composite video mods", R3UK, 2004, updated 2008 (a UK PAL "Revision A" Atari Jr.): five screws, the SELECT and RESET ribbon cable, and the grounded area round the regulator.
  11. ↑ Evan-Amos, photograph of an Atari 2600 Jr. with the top case removed, Wikimedia Commons, public domain. Hosted here as File:Atari 2600 Jr with top case removed.jpg.
  12. ↑ 12.0 12.1 12.2 12.3 Texas Instruments, LM340, LM340A and LM7805 Family Wide VIN 1.5-A Fixed Voltage Regulators, datasheet SNOSBT0L, revised September 2016: TO-220 pin functions (section 5) and the LM7805 electrical characteristics (section 6.6), including the 4.75 to 5.25 V output range and the 7.5 V minimum input. ti.com.
  13. ↑ Atari, Field Service Manual FD100133 Rev. 02, figure 2-1, "2600/2600A IC Pinouts", p. 2-3: regulator pins in, ground, out.
  14. ↑ Atari, Field Service Manual FD100133 Rev. 02, "2600A Snowy Screen Troubleshooting Procedure", p. 6-12: the check for a shorted +5 V line.


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