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Atari Lynx II Troubleshooting Guide

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Atari Lynx II motherboard (C104471-001 Rev A)
Lynx II board C104471-001 Rev. A. The power circuit is at the top left: C41, C39, Q12 below them, D13 to its right, and the transformer T1 lower down

Fault-finding on the Atari Lynx II, using Atari's schematic C104247 Rev. 1, the 1991 owner's manual, and repair notes from the Atari Lynx Vault, Retro Isle and Igor Kromin's repair log.[1][2] The schematic is an engineering issue drawn for the Hayato version of the board; the power and button circuits match the production boards' designators, but some audio parts differ (see Atari Lynx II Capacitor Replacement Guide). The original Lynx is covered by Atari Lynx Troubleshooting Guide, and disassembly by Atari Lynx II General Maintenance.

Before you start

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Work through Atari's own checks first. The owner's manual's troubleshooting table gives:[2]

Owner's manual troubleshooting (1991)
Problem Atari's remedy
No picture, single player Turn up the brightness; make sure the power is on; check the adaptor connection; fit or replace batteries
No picture, multiplayer If the power light is on, check that the backlight is switched on; switch all units off, then on within 7 seconds of each other
Picture too dark or too light Adjust the brightness from directly in front of the screen; if the power light is on and the screen is totally dark, switch the backlight on
Erratic game operation or screen flicker Fit the batteries correctly or change them
No sound Adjust the volume
Sound distorted or weak Replace the batteries
Software does not respond to controls Restart, or switch off and on again
  • Put a known-good cartridge in the slot. Game cards connect cartridge pin 31, which supplies the soft-power inverter, to pin 33, so the Lynx II does not switch on without one.[3]
  • INSERT GAME on the screen means the console is running; clean the cartridge contacts or try another cartridge.[4]
  • If the Lynx does not start, do not keep pressing ON with batteries or the adaptor connected. The Atari Lynx Vault warns that a failed power circuit can put 9 V into the chips; check the board with the regulator bypassed first.[4][5]

Will not switch on

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The power circuit

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The ON and OFF buttons on the membrane set a latch built from two gates of the 4069 hex inverter U6 (U6F and U6E); TP17 (ON-HI) and TP18 (ON-LOW) are on its two sides. The remaining gates of U6 drive the MOSFET Q12 (MTD3055E), which switches the 100 µH inductor L15, with the Schottky diode D12 (1N5817), the input capacitor C39 and the output capacitor C41. The 2N3906 transistor Q8, the 120 Ω resistor R74 and the 4.3 V zener D13 (1N5991B) set the output voltage; the schematic labels the zener junction TP19 "ZERO" and the output TP15 "+5V". Q7, also a 2N3906, is part of the ON/OFF switching circuit.[1]

Orange-Phantom, quoted by the Atari Lynx Vault, describes this as a true switching regulator: the zener is the voltage reference for the inverter that switches Q12 at high frequency, and if the zener is removed the inverter stops switching and 9 V goes straight into the Lynx.[6]

Measurements

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  • With the adaptor connected and only the power lead plugged into the board, the adaptor voltage, less the drop of the input diode, appears across C39. With the Lynx switched on there is about 5 V across C41.[7] Orange-Phantom measured the input diode drop as 0.7 V.[6]
  • The schematic's test points (below) give the rest.[1]

Dead or alive test

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The Atari Lynx Vault's method bypasses the regulator:[4]

  1. Open the Lynx and find C41, the 470 µF capacitor at the top left of the board.
  2. Solder the red lead of a cut-down USB cable to the positive leg of C41 on the underside, and the black (or white) lead to the negative leg.
  3. Insert a cartridge and plug the USB lead into a 5 V supply rated for at least 1 A. The Lynx starts without the ON button.
  4. A game or INSERT GAME means the board is alive and the power circuit is at fault. A black or white screen or other glitches mean the board itself has probably failed.

Warning: use 5 V only. More than 5 V at C41 destroys the processor and possibly other chips.[4] The Vault also sells a cable that does the same through the ComLynx socket without opening the case.[4]

Parts to replace

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Lynx II power-circuit parts
Ref Part (Atari schematic) Location and notes
Q12 MTD3055E N-channel MOSFET Below C39 at the top left. Snip the two legs close to the body, then heat the tab and lift the part off.[5] Retro Isle gives the STD12N06 as a current replacement with the same pinout.[7]
D13 1N5991B, 4.3 V zener Surface-mount, to the right of Q12 under the brightness wheel. A through-hole replacement is bent to fit the pads, stripe towards the RF shield and R74.[5]
Q7, Q8 2N3906 Near the power socket. They fail less often than the MOSFET and zener but can also stop the Lynx starting.[8]
U6 4069 hex inverter The Atari Lynx Vault reports that it can fail and leave the ON and OFF buttons with no effect.[9]

Designators and part types are from the schematic;[1] locations are from the Atari Lynx Vault's guides and K-Retro's map.[5][10]

Power jack

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The jack's internal pin can break off where it meets the board. Replace the jack (Best Electronics part CB102242 for the Lynx II) and glue it on both sides with hot-melt glue so it cannot rock.[7] The Atari Lynx Vault's guide covers removing the old glue and desoldering the three pins.[11]

Test points

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Lynx II test points (schematic C104247)
Test point Label on the schematic Connected to
TP15 +5V Regulated output and C41
TP19 ZERO Junction of the zener D13 and R74
TP16 B- Battery negative
TP17 ON-HI ON side of the soft switch, with C37 and R68
TP18 ON-LOW OFF side of the soft switch, at U6F pin 13
TP12 +20V LCD supply from the backlight transformer, with C23
TP21 V18 LCD bias circuit
TP24, TP25 VM, VD2 LCD bias lines, with C27 and C28
TP22, TP23 LCD VDD, LCD VSS LCD module supply
TP20 SWITCHED VCC Switched supply to cartridge pin 34
TP11 SPEAKER LM386 output, after C36
TP1 RESET/ Processor reset, with C3 and D1
TP2 to TP10 DOWN, UP, RIGHT, LEFT, OUTSIDE, INSIDE, OPTION2, OPTION1, PAUSE Button lines into Suzy

Buttons

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The buttons connect to the board through the 14-pin JP2 ribbon. Pressing any button except the soft power switches joins its line to pin 14, which carries +5 V on the schematic, so the button's test point should go high while the button is held.[3][1]

The Atari Lynx Vault's checks on the membrane:[12]

  1. Look at the fingers at the ribbon end. Worn or broken printing there stops buttons working; trim up to about 3 mm off the end and push the ribbon fully home.
  2. With the membrane out and the rubber pads removed, measure each button's pair of fingers on the 200 kΩ range. Unpressed, every button should read open circuit. A reading means carbon dust or sticky residue is bridging the traces somewhere along their length; clean them.
  3. Pressed, a good contact reads about 200 Ω; up to 20 kΩ still works, but a high reading means the membrane is wearing out.
  4. If the membrane tests good and a button still does nothing, the pad's carbon face may have hardened. Rub it lightly on clean white paper until it leaves a black trail.

Screen faults

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  • A dark screen with the power light on: press the backlight button first.[2] The tube is driven by T1 and the 2SD965 transistors Q13 and Q14 from the +5 V rail through L17, and the backlight-off circuit uses U11 (74HC74).[1]
  • Black lines across the picture, with poor colour: Igor Kromin's Lynx II showed this, and a full recap cured it.[13][14]
  • Dim or washed-out picture: the Atari Lynx Vault lists display faults among the reasons to recap.[9] A replacement LCD kit removes the original panel and tube; see Atari Lynx II LCD & Backlight Mod.

Sound faults

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  • Plug in headphones. If they are loud and clear but the speaker is quiet or crackles, suspect the speaker. Retro Isle reports speakers damaged by the 9 V adaptor being plugged into the headphone socket.[7] Igor Kromin's recapped Lynx II stayed very quiet until he swapped the speaker, after confirming good sound through headphones.[15]
  • The speaker is 40 mm, 16 Ω.[7][1] An 8 Ω 40 mm speaker fits and plays louder.[15]
  • Crackling sound: Igor Kromin's crackle went with the recap.[14] The speaker amplifier is an LM386 (U5) and the headphone amplifier an NJM2073 (U12).[1]
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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 Corporation, Schematic Diagram, Lynx II (Hayato), drawing C104247 Rev. 1 (engineering issue), 29 June 1990, sheet 1: power section, button connector JP2 and test points, backlight, audio. Hosted here as File:Atari Lynx II schematic C104247 Rev 1.png.
  2. ↑ 2.0 2.1 2.2 Atari Corporation, Lynx Portable Color Entertainment System Owner's Manual, 1991, "Troubleshooting", pp. 14-15. Hosted here as File:Atari Lynx II Owner's Manual (1991).pdf.
  3. ↑ 3.0 3.1 Atari Lynx Vault, "Atari Lynx Hardware Notes" (changed 3 October 2023), cartridge and button pinouts, reproduced with permission from Osman Celimli. Community source.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Atari Lynx Vault, "Atari Lynx Dead/Alive Test - Bypassing The Atari Lynx 9V" (changed 6 November 2023). Community source.
  5. ↑ 5.0 5.1 5.2 5.3 Atari Lynx Vault, "Replacing the MOSFET and zener diodes in an Atari Lynx" (changed 4 October 2023). Community source.
  6. ↑ 6.0 6.1 Atari Lynx Vault, "Power draw inefficiencies measured for the Atari Lynx McWill mod" (changed 8 November 2023), quoting Orange-Phantom's 2015 measurements and notes. Community source.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 Retro Isle, "Lynx Repair Info": MTD3055E replacement, DC power jack, no sound. Community source.
  8. ↑ Atari Lynx Vault, "Replacing the 3906 transistors on an Atari Lynx" (changed 5 October 2023). Community source.
  9. ↑ 9.0 9.1 Atari Lynx Vault, "Atari Lynx Hardware Mods" (changed 9 October 2023). Community source.
  10. ↑ Atari Lynx Vault, "Atari Lynx Capacitor Maps" (changed 4 October 2023): K-Retro's Lynx 2 component map. Vendor-published community source.
  11. ↑ Atari Lynx Vault, "Replacing the power socket on an Atari Lynx" (changed 5 October 2023). Community source.
  12. ↑ Atari Lynx Vault, "Troubleshooting Lynx Model 2 buttons and D-pad" (changed 5 October 2023). Community source.
  13. ↑ Igor Kromin, "Atari Lynx repair - Part 1 - introduction and case disassembly", 11 September 2017. Personal repair log.
  14. ↑ 14.0 14.1 Igor Kromin, "Atari Lynx repair - Part 2 - re-capping the motherboard", 12 September 2017. Personal repair log.
  15. ↑ 15.0 15.1 Igor Kromin, "Atari Lynx repair - Part 3 - broken speaker replacement", 13 September 2017. Personal repair log.


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