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Atari 2600 Colour Adjustment

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Atari 2600 six-switch motherboard colour delay control R211
The colour delay control R211 (CLR DLY ADJ) on a six-switch motherboard, with the crystal X200, the oscillator transistors Q200 and Q201, and CR200, CR201, C208 and C209 below it (photo: Evan-Amos, public domain)

The Atari 2600 has one adjustment for colour: a potentiometer that sets the TIA's colour delay, R211 on the six-switch CX2600 and R213 on the four-switch CX2600A.[1] Atari sets it during the colour bar test of its Diagnostic Test Cartridge.[1] Skooter Blog found the colours drift as the console warms up, and retro64 had a console that showed black and white for ten minutes before colour appeared, cured by turning the pot a little.[2][3] When the colour cannot be set, Atari's colour troubleshooting charts trace the fault through the crystal, the diodes that feed the delay control and the TIA's colour output.[4][5]

The procedures are for NTSC consoles, the domestic models in Atari's manual. A PAL TIA in an NTSC console gives wrong colours; Atari's NTSC TIA is C010444, and Tynemouth Software reports the PAL part marked C011903.[6][7]

Symptoms

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  • Colours that are slightly wrong in every game, or that change as the console warms up: an adjustment.[2]
  • No colour at all, only the reference bar, or colour that will not adjust: a fault. Atari's checklists name the parts round the colour circuit (below).[8]
  • Grainy colour with faint vertical bars on a CX2600A: Atari's Field Change Order 1A puts it down to 12 V radial capacitors at C241 and C242; see Atari 2600 Capacitor Replacement Guide.[9]
  • Colour that cannot be set on a console with a failing regulator or a leaking 2200 µF reservoir. retro64 could not adjust the 2600-mode colour of an Atari 7800 until he had replaced both; on the 2600A the colour delay network is fed from the switched supply through a 4.7 kΩ resistor, with two diodes to +5 V.[3][10] Check the supply first: Atari 2600 Power Supply Circuit Repair.
Atari's checklist causes for colour faults
Symptom CX2600 (motherboard; switchboard) CX2600A
No colour X200, A201; L101, RF module, RF cable X200, A201, C210, C211, RF cable
Only the reference bar appears C208, R211 R213, C205, A201
Colour will not adjust R211, C208, C209 R213, C205, CR200, CR201
Weak colour C212, C213, R215; RF module, L101, RF cable RF module, C210, C211, R210, RF cable

The table is from Atari's symptom checklists.[8]

Tools

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  • A small flat-blade screwdriver for the potentiometer, and a colour television on the RF input the console will normally use.
  • A test pattern. Atari used its Diagnostic Test Cartridge, version 2.6, part MA017600.[11][9] Skooter Blog used the homebrew Color Bar Generator by VideoSoft, run from a Harmony cartridge.[2] Best Electronics and Vintage Gaming and More use ordinary games whose colours they know.[12][13]
  • For fault-finding: a multimeter and an oscilloscope; Atari's procedures also use a frequency counter.[11]

Procedure

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Getting to the control

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Atari 2600 CX2600A regulator A203 area (Rev 16)
R213, the white potentiometer to the right of the regulator, on a Rev 16 four-switch board (photo: Evan-Amos, public domain)
  1. Open the console as in Atari 2600 Power Supply Circuit Repair#Opening the console. Leave the board connected so that the console can run.[13][14]
  2. Find the pot. Vintage Gaming and More describes it as the big plastic circle at the bottom left of the board, the only pot on it, on both four-switch and six-switch boards.[13][14] It is R213 on the CX2600A, outside the shield, and R211, marked CLR DLY ADJ, on the CX2600 motherboard.[15][16]
  3. Connect the power, the television and, on a six-switch console, the switchboard cable.[14]

Adjusting with Atari's test cartridge

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  1. Set all the console switches to their initial positions (on the CX2600A, front switches up and rear switches to the left), insert the Diagnostic Test Cartridge and switch on.[17]
  2. The colour bar screen appears: horizontal colour bars with a thin grey or blue reference line about three bars from the bottom.[1]
  3. Turn R211 or R213 until the bars immediately above and below the reference line are within one shade of each other.[1]
  4. Leave the test running for at least ten seconds and watch for a bar that changes colour or blanks.[1]
  5. If the colours cannot be brought into line, go to the fault-finding steps below.[18][19]

Adjusting with a colour bar program

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Skooter Blog's method, worked out with advice from AtariAge member Trebor:[2]

  1. Let the console stand switched off for at least 45 minutes so that it is cold.
  2. Switch on and start Color Bar Generator straight away.
  3. Turn the pot until the top and bottom of the program's opening screen show the same colour. Work quickly: as the console warms, the bottom of the screen darkens towards brown while the top stays green.
  4. Switch off, let the console cool for at least 45 minutes again, and check that the top and bottom still match from a cold start. Skooter needed four or five rounds; the pot is sensitive.

Adjusting with known games

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  • Best Electronics' references for an NTSC console set to Atari's standard: a green band at the bottom of the Space Invaders screen, orange at the bottom of Missile Command, an off-green strip at the bottom of Pac-Man and a full screen of bright green in Casino.[12]
  • Vintage Gaming and More suggests a game with many bright colours that you know well, such as Frogger or Pitfall.[13]
  • retro64 lets the console warm up before adjusting.[3]

Finding the fault when the colour will not adjust

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Atari's charts check the following points. Work through the table for your board, then swap the TIA (A201), the 6532 (A202) and the 6507 (A200) in turn if the readings are good.[4][5]

CX2600 colour checks (Atari pp. 4-21, 4-22)
Check Expected If wrong
X200 frequency 3.546 MHz ±0.04 MHz as printed on Atari's chart X200 defective
TIA (A201) pin 10 with R211 fully anticlockwise 6.5 to 7.5 V If correct, swap A201, A200, A202
Cathode of CR201 +6 to 7 V If present but pin 10 is wrong: C208, C209, R211, or an open track from CR201 to A201 pin 10
Cathode of CR200 3 to 5 V peak to peak If present but CR201 is wrong, CR200 or CR201 is defective; if absent, look for an open or shorted track to the diodes
Weak or no colour: between C213 and R215 3.5 to 5 V peak to peak If present, R215 defective
Between C212 and C213 3.5 to 5 V peak to peak If present, C213 defective
A201 pin 9 3.5 to 5 V peak to peak If present, C212 defective; if absent, pin 9 is shorted to another line
CX2600A colour checks (Atari pp. 6-16 to 6-18)
Check Expected If wrong
No colour at all: between R210 and C211 2 to 2.5 V peak to peak on a 2.5 V level If present, check the crystal, the RF modulator tuning, R213 and the RF cable (next rows)
Between C210 and C211 2.5 to 3 V peak to peak on a 3 to 3.5 V level If present, replace C211
Between C210 and R228 4.5 to 5 V peak to peak If present, replace C210
TIA pin 9 4.5 to 5 V peak to peak If present, the track from TIA pin 9 to C210 is open; if absent, check R228 and R211, then swap A201, A202, A200
Crystal (X200; Y200 on the chart) 3.5795 MHz ±0.004 MHz Crystal, or the oscillator transistors Q200 and Q201
RF modulator Tuned to 61.25 MHz ±0.15 MHz Tune it, or replace it if it will not tune
Some colour but it will not set: TIA pin 10 while R213 is turned The voltage changes, up to about 6 V (the lower figure is not legible in the scan) If it changes and the crystal is right, swap A201, A200, A202
Anode of CR200, with R213 fully clockwise 6 V If present, R213 is defective or open to A201
Anode of CR201 5.5 V If present and R212 is good, CR200 is defective
Cathode of CR201 +5 V If present, CR201 is defective; if absent, the feed from +5 V is open
Colour constantly rolling or cycling Seen on the screen C205, then A201

Testing

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  • Run the colour bar test again: the bars either side of the reference line should be within one shade, and no bar should change colour or blank for at least ten seconds.[1]
  • Switch the TV-type switch to black and white and check the grey bar test: eight grey bars from black to white with no colour anywhere.[20]
  • Recheck after the console has run for a while and again from cold, as Skooter Blog does.[2]
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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Atari, Field Service Manual FD100133 Rev. 02, "Color Bar Test", p. 3-9: the reference line, the R211 (R213 on the 2600A) adjustment to within one shade, and the ten-second watch.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Skooter Blog, "Ajustando as cores do Atari 2600 - Parte 2", 13 March 2017 (Portuguese): adjusting with Color Bar Generator from a cold start, the drift towards brown as the console warms, and the 45-minute cooling between checks.
  3. ↑ 3.0 3.1 3.2 retro64, "Atari 2600 and 7800: repair tales": a 2600 that showed black and white for ten minutes before colour appeared, adjusted after warm-up, and a 7800 whose 2600-mode colour could be set only after the 7805 and the 2200 µF capacitor were replaced.
  4. ↑ 4.0 4.1 Atari, Field Service Manual FD100133 Rev. 02, "Color Troubleshooting Procedure, Motherboard", pp. 4-21 and 4-22.
  5. ↑ 5.0 5.1 Atari, Field Service Manual FD100133 Rev. 02, "2600A Color Troubleshooting", pp. 6-16 to 6-18.
  6. ↑ Atari, Field Service Manual FD100133 Rev. 02, Section 8 parts lists: TIA C010444 at A201.
  7. ↑ Dave Curran, "Atari 2600 Black Screen Repair", Tynemouth Software, February 2015: PAL TIA marked C011903.
  8. ↑ 8.0 8.1 Atari, Field Service Manual FD100133 Rev. 02, Section 5 symptom checklists, colour failures, pp. 5-3 and 5-6.
  9. ↑ 9.0 9.1 Atari, Inc., Atari 2600 and Atari 5200 Field Change Orders, Upgrade Bulletins, Tech Tips: Field Change Order 1A (2600A, 19 July 1982) and the test cartridge part numbers in Tech Tip 1. Hosted as File:Atari 2600 and 5200 Field Change Orders and Tech Tips.pdf; see Atari 2600 and 5200 Field Change Orders and Tech Tips.
  10. ↑ Atari, Inc., Video Computer System (Main Board) schematic, CX-2600A, sheet 2 of 4, 30 May 1982: the 500K colour delay pot to TIA pin 10, the 4700 Ω feed from the switched supply and the two 1N914 diodes to +5 V. Hosted as File:Schematic Atari2600A 2000.png.
  11. ↑ 11.0 11.1 Atari, Inc., Video Computer System Field Service Manual, Domestic Model 2600/2600A, FD100133 Rev. 02, "Equipment Requirements", p. 3-1. Hosted as File:Atari 2600 and 2600A Field Service Manual.pdf; see Atari 2600 and 2600A Field Service Manual.
  12. ↑ 12.0 12.1 Best Electronics, "What to look for when buying a used or third party reconditioned Atari 2600 / 2600A / 2600Jr console", tip 6: video and colour test with known games.
  13. ↑ 13.0 13.1 13.2 13.3 Vintage Gaming and More, "Atari 2600 4 Switch Tune Up Kit Installation Guide": the colour potentiometer and adjusting it with a familiar colourful game.
  14. ↑ 14.0 14.1 14.2 Vintage Gaming and More, "Atari 2600 6 Switch Tune Up Kit Installation Guide": the colour potentiometer on the six-switch motherboard, adjusted with power, ribbon and television connected.
  15. ↑ Evan-Amos, "Atari-2600-Four-Switch-Motherboard-Flat.jpg", Wikimedia Commons, public domain: R213 on a Rev 16 CX2600A, outside the shield.
  16. ↑ Evan-Amos, "Atari-2600-Six-Switch-Motherboard-Flat.jpg", Wikimedia Commons, public domain: R211 marked CLR DLY ADJ on a CX2600 motherboard.
  17. ↑ Atari, Field Service Manual FD100133 Rev. 02, "Initialization", p. 3-7, and figure 3-6.
  18. ↑ Atari, Field Service Manual FD100133 Rev. 02, "Color Bars Test Procedure", p. 4-6.
  19. ↑ Atari, Field Service Manual FD100133 Rev. 02, "2600A Color Bars Test Procedure", p. 6-7.
  20. ↑ Atari, Field Service Manual FD100133 Rev. 02, "Gray Bar Test", p. 3-10.


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