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Atari 2600 Jr Troubleshooting Guide

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Atari 2600 Jr motherboard (angled view)
NTSC 2600 Jr. board; the regulator is on the copper pad at the front left

Fault-finding on the Atari 2600 Jr. Atari's 2600 field service manual stops at the CX2600A, so there is no Atari flowchart for the Jr.[1] The Jr. uses the same 6507, 6532 and TIA as the earlier consoles, so Atari's chip-level tests and pin assignments still apply, but its board, designators and power circuit are its own.[1][2] Designators below are from the photographed NTSC board and from Jerzy Sobola's redrawn PAL schematic, which share them.[2][3]

Before you start

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  • Try a known-good cartridge and controller, and clean the cartridge contacts.
  • Check the adaptor. The owner's leaflet warns that an adaptor not designed for the 2600 can damage the console.[4]
  • Set the channel selector on the back to match the television (channel 2 or 3).[4]
  • Atari's Diagnostic Test Cartridge 2.6 tests the RAM, colour bars, grey bars, a diagnostic matrix, audio tones and the paddle lines. The tests are described on the Atari 2600 Troubleshooting Guide; they check the chips, so they work the same way on a Jr.[1]

No power, no LED

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Power path (PAL schematic)
Point What to check
Adaptor DC output with the console unplugged
Power jack J2 Loose, dirty or cracked joints. Console5's notes for the 2600 family say the jacks often work loose and a tap on the plug can reset the console[5]
Reservoir C26 (2200 µF) Adaptor voltage present; bulging or leakage
Power switch S4 Voltage on both sides with the switch on
C37 and regulator input Same voltage after the switch
Regulator VR1 (7805) output +5 V. Console5 says the original regulators run close to their rating and often fail[5]
LED DS1 and R57 (750 Ω) If +5 V is present but the LED is dark

Positions are from the PAL schematic.[3] If the regulator runs hot or the fault comes and goes, check that it is fixed to its copper pad: TBA has found Jr. consoles with nothing holding it down and recommends soldering the tab or fitting a screw.[6]

Power on, no picture

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  • Check the RF path: the channel switch, the RF cable at J4 and the television's tuning.[4]
  • Check +5 V and ground at each LSI chip. Atari's CX2600A schematic gives the supply pins: 6507 Vcc pin 4, 6532 Vcc pin 20, TIA Vcc pin 20.[7][1]
  • Check the 6507 reset (pin 1) goes high after power-up. On the Jr. the reset circuit uses one section of the 4050 at A4, so a faulty 4050 can hold the processor in reset as well as upset the picture.[3][6]
  • Check the colour clock at the crystal Y1 and its oscillator transistors Q1 and Q2. The PAL schematic shows a 3.54 MHz crystal (Atari C016112).[3]
  • The three LSI chips on the photographed NTSC board are soldered in. Swapping them means desoldering; test the supply, clock and reset first.[2]

Picture faults

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Picture symptoms
Symptom Where to look
No colour, or colours wrong Trimmer R9 on the TIA's colour-adjust pin;[3] the crystal and the TIA. On the CX2600A Atari's checklist gives the crystal and the TIA for no colour, and the colour control and the capacitor beside it for colour that will not adjust[1]
Grey bars wrong, or sync lost The 4050 at A4, which buffers the luminance and sync lines, and the summing resistors after it[3]
Snow or a weak picture RF output: the modulator section around A5 (CA3086 or LM3086) and its supply[3][2]

Set R9 with a colour-bar pattern. Atari's method on the CX2600A is to adjust until the bars above and below the thin reference line are within one shade of each other.[1]

No sound

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The TIA's audio goes to the sound-carrier oscillator around Q4 (2N3563), the adjustable coil L8 and the 820 pF capacitors C53 and C54.[3]

  1. Check the television's volume and tuning.
  2. Replace C53 and C54 as a pair. On the CX2600 and CX2600A, Atari's tech tip 2 names the equivalent pair as the primary suspects for audio failures and notes that pressing on them can bring the sound back.[1] Console5 lists the Jr.'s C53 and C54 and calls the 2600's polystyrene pair "next in line for failure, causing a loss of audio".[5]
  3. Retune L8 for the sound carrier. Atari's tip 16 says the CX2600A's coil needs replacing only if the carrier cannot be adjusted.[1]

Controls

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  • SELECT or RESET does nothing: the two buttons reach the board through J6 on a flexible cable, which has to be unplugged whenever the top case comes off. Check that it is fully seated.[3][8][6]
  • A slide switch that misbehaves: the board has five, S1 to S5; S4 is the power switch.[2][3]
  • Joystick directions or fire button dead: the direction lines go to the 6532 and the trigger lines to the TIA, each with a small filter capacitor at the port.[3][1] Controller repairs are on the Atari 2600 General Maintenance page.
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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Atari, Inc., Video Computer System Field Service Manual, Domestic Model 2600/2600A, FD100133 Rev. 02: diagnostic test cartridge 2.6, symptom checklist, IC pinouts and NTSC tech tips 2 and 16. It does not cover the 2600 Jr. Hosted here as Atari 2600 and 2600A Field Service Manual.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Evan-Amos, photograph of an NTSC Atari 2600 Jr. motherboard, Wikimedia Commons, public domain. Hosted here as File:Atari-2600-Jr-Motherboard-Flat.jpg.
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 Jerzy Sobola, redrawn schematic "Motherboard C012283 rev. B, Atari 2600 Game Console", sheet 1 of 2, 8 September 2000 (PAL 2600 Jr.). Hosted here as File:Atari 2600 Jr PAL motherboard schematic (Jerzy Sobola).png.
  4. ↑ 4.0 4.1 4.2 Atari Corp., Atari 2600 owner's leaflet for the 2600 Jr., C026260-001, 1986. Hosted here as File:Atari 2600 Jr Owner's Manual C026260-001.pdf.
  5. ↑ 5.0 5.1 5.2 Console5 TechWiki, "Atari 2600", refresh-kit notes (7805, DC jack) and the Junior capacitor lists. Secondary source.
  6. ↑ 6.0 6.1 6.2 The Brewing Academy, Bryan's Ultimate Atari Video Rev. D Instruction Manual, revision 1.94, 23 March 2021, "Atari 2600 Jr." (p. 12). PDF from thebrewingacademy.com.
  7. ↑ Atari, Inc., Video Computer System (Main Board) schematic, CX-2600A, sheet 2 of 4, 30 May 1982. See File:Schematic Atari2600A 2000.png.
  8. ↑ David Savery, "Atari 2600 composite video mods", R3UK, 2004, updated 2008. Community project write-up.


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