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Atari 5200 Joystick Pot Line Repair

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Atari 5200 pot control line flowchart (FSM p. 4-17)
Atari's pot control line chart and the table of pot line error codes, port pins, POKEY pins, capacitors and resistors (field service manual p. 4-17)

The Atari 5200 reads each analogue joystick through two of the eight pot lines of the POKEY chip (U7 on the original four-port board CA018087, A7 on the later boards). The controller's two potentiometers sit between a supply called +CAV and the pot line, and the voltage on +CAV is set by the console's trimmer R132 through the transistors Q11 to Q14.[1][2][3] A failing pot line shows up as one of the error codes 22 to 29 on Atari's diagnostic cartridge. Some CA018087 boards also show paddle jitter, which Atari traced to ripple on the POKEY's +5 V supply and fixed with Tech Tip 14.[4] The steps below follow Atari's pot control line chart and that tech tip. A controller that fails on every console is covered by Atari 5200 Controller Flex Circuit and Potentiometer Repair.

Symptoms

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  • The diagnostic cartridge's error summary shows a code from 22 to 29. Each code is one pot line: 22 and 23 are port 1 horizontal and vertical, 24 and 25 port 2, 26 and 27 port 3, 28 and 29 port 4.[5][1]
  • On the Pokey Adjust screen the values cannot be brought into range: Atari sets port 1 horizontal to 112 ± 1 with R132, after which every other value should read between 100 and 124.[6]
  • The joystick jitters in play on a CA018087 board: Atari's Tech Tip 14.[4]

Try a known-good controller first. Atari's controller tests are on Atari 5200 Controller Flex Circuit and Potentiometer Repair.[7]

Tools and parts

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  • A multimeter, the Diagnostic Cartridge 1.1, a known-good controller, and for the Q11 to Q14 readings in Port Test mode no port (loop-back) board.[2][8]
  • Known-good POKEY (U7 or A7) and GTIA (U5 or A5) chips to swap in. Both are socketed on all three boards.[2][9]
  • For Tech Tip 14: a 10 µF 20 V tantalum capacitor (Atari C017516), about 2 inches of 16 gauge bus wire and 4 inches of 16 gauge plastic sleeving.[4]

Pot lines

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Pot lines (FSM p. 4-17)
Error code Pokey Adjust failure Port and pin POKEY (U7) pin Capacitors Resistor
22 HOR 1 1-10 14 C98, C106 R106
23 VERT 1 1-11 15 C97, C105 R110
24 HOR 2 2-10 12 C96, C104 R107
25 VERT 2 2-11 13 C95, C103 R111
26 HOR 3 3-10 10 C94, C102 R108
27 VERT 3 3-11 11 C93, C101 R112
28 HOR 4 4-10 8 C92, C100 R109
29 VERT 4 4-11 9 C91, C99 R113

On the controller, pin 10 is pot 2 (horizontal), pin 11 pot 1 (vertical) and pin 9 +CAV.[10]

Procedure

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Following Atari's chart

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Read U as A on a CA020108 board.[1]

  1. Run the diagnostic cartridge and select the Pokey Adjust test.[1]
  2. Measure +CAV on the failing port (pin 9) and turn R132. If it can be set anywhere between 4 and 6.4 V, go to step 3. If not, go to the +CAV checks below.[1][10]
  3. Swap U7 for a known-good POKEY and run the test again. If the pot lines pass, the old POKEY was faulty.[1]
  4. If they still fail, use the error code and the table above to find the failing line, and check that line's two capacitors and resistor for the correct value.[1]
  5. If the parts are good and the line still fails, look for an open or shorted trace between the port pin and the POKEY pin and repair it.[1]
  6. Set R132 so that port 1 horizontal reads 112 ± 1 on the Pokey Adjust screen, and check that every other reading is between 100 and 124.[6]

+CAV checks

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Atari 5200 pot control line flowchart (FSM p. 4-18)
The +CAV checks and the Q11 to Q14 voltages for the A and B conditions (field service manual p. 4-18)
  1. Swap U5 (GTIA), then U7 (POKEY), for known-good chips. If +CAV can now be set, the console is repaired.[2]
  2. If not, measure Q11 to Q14 on the Pokey Adjust screen (condition A) and compare with the table below. Replace any transistor that reads wrongly, then check that Pokey Adjust passes; if it still does not, a component in the Pokey Adjust circuit is faulty.[2]
  3. If the condition A readings are correct, put the console in Port Test mode without the port board and measure again (condition B). Replace any transistor that reads wrongly. If they are all correct, look for opens and shorts in the circuit and repair them.[2]
Q11 to Q14 (FSM p. 4-18); A = Pokey Adjust screen, B = Port Test without the port board
Q11 A Q11 B Q12 A Q12 B Q13 A Q13 B Q14 A Q14 B
Emitter 13 V 13 V 3.2 V 0 V 0 0 3.2 V 0 V
Base 12 V 13 V 4 V 0 V 0 0.7 V 3.8 V 0 V
Collector 4 to 6.4 V 0 V 13 V 13 V 3.8 V 0 V 12 V 13 V

The parts list gives Q11 as a 2N3906 and Q12 to Q14 as 2N3904; R132 is a 1 kΩ trimmer (C019103).[9] On Atari's schematic the network is labelled "joystick centering".[3]

Atari 5200 four-port motherboard power switch circuit (A26, S2, Q6 to Q10)
The right-hand end of a four-port board: the R132 trimmer (blue) and Q13 and Q14 are at the bottom of the photograph (photo: Evan-Amos, public domain)

Paddle jitter on CA018087 (Tech Tip 14)

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Atari 5200 Tech Tip 14 paddle jitter wire (figure 1)
Solder side of the CA018087 board: pin 1 of U7 and the ground lead of C104, the two ends of the sleeved wire (Tech Tip 14, figure 1)

Atari's Tech Tip 14 (3 July 1983) applies to CA018087 boards that show paddle jitter. Atari traced it to ripple on the +5 V supply to the POKEY and an inadequate ground trace at U7 pin 1, and asks for the seven steps to be done only on boards that show the fault.[4]

  1. Trim the 10 µF tantalum capacitor to an overall length of 1⅝ to 1¾ inches.[4]
  2. Cover its leads with sleeving, leaving about ⅛ inch of each lead bare for soldering.[4]
  3. Solder the + lead to U7 pin 17 (+5 V), on the chip's leg.[4]
  4. Solder the other lead to U7 pin 1 (ground), on the chip's leg.[4]
  5. Cover 1¼ inches of bus wire with plastic sleeving, leaving enough bare wire at each end to solder.[4]
  6. On the solder side of the board, solder one end of the sleeved wire to U7 pin 1.[4]
  7. Solder the other end to the ground lead of C104.[4]

Testing

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  • Pokey Adjust: port 1 horizontal at 112 ± 1 after setting R132, every other value between 100 and 124.[6]
  • Run the port test with the port board fitted; codes 22 to 29 should no longer appear on the error summary.[5][8]
  • After Tech Tip 14, Atari's test is to reassemble the console and play a game, checking that the jitter has gone.[4]
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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 Atari, CX5200 Field Service Manual FD100127 Rev. 4, "Pot Control Line Troubleshooting", p. 4-17, with the table of pot lines.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Atari, CX5200 Field Service Manual FD100127 Rev. 4, "Pot Control Line Troubleshooting (Cont.)", p. 4-18, with the Q11 to Q14 voltages.
  3. ↑ 3.0 3.1 Atari, Inc., Atari 5200 Programmable Video Game System schematic, main board sheet (I/O section: POKEY, the controller port pot lines and the "joystick centering" network). See File:Schematic Atari5200 4000.png.
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 Atari, Inc., Tech Tip VCS 14, "Paddle Jitter on CX5200 PCB (P/N CA018087)", 3 July 1983, with figure 1, in Atari 2600 and Atari 5200 Field Change Orders, Upgrade Bulletins, Tech Tips. Hosted here as Atari 2600 and 5200 Field Change Orders and Tech Tips.
  5. ↑ 5.0 5.1 Atari, CX5200 Field Service Manual FD100127 Rev. 4, Table 3-1, "Diagnostic Error Codes", p. 3-9.
  6. ↑ 6.0 6.1 6.2 Atari, CX5200 Field Service Manual FD100127 Rev. 4, "Pokey Adjust", p. 3-7, and figure 3-4, p. 3-8.
  7. ↑ Atari, CX5200 Field Service Manual FD100127 Rev. 4, section 6, controller tests, pp. 6-3 to 6-5.
  8. ↑ 8.0 8.1 Atari, Inc., CX5200 Field Service Manual, FD100127 Rev. 4, July 1983, section 3, pp. 3-1 and 3-2: the diagnostic cartridge 1.1 and the port (loop-back) board. Hosted here as Atari CX5200 Field Service Manual.
  9. ↑ 9.0 9.1 Atari, CX5200 Field Service Manual FD100127 Rev. 4, section 8, parts lists for CA018087, CA020108 and CA021374: Q11 to Q14, R132, U5/A5, U7/A7 and the IC sockets.
  10. ↑ 10.0 10.1 Atari, CX5200 Field Service Manual FD100127 Rev. 4, figure 6-9, "CX52 Game Controller Schematic", p. 6-13.


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