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Atari Lynx Capacitor Replacement Guide

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Component side of an original Lynx board, C103949-001 Rev. 1. C38 and C39 stand beside the speaker at the top left; the backlight assembly sits in the middle

The original Atari Lynx main board has fifteen or sixteen aluminium electrolytic capacitors, depending on the board revision. Atari's schematic for the board, drawing C104019 Rev. C, gives the value and voltage of every one of them.[1] The capacitor map that K-Retro publishes through the Atari Lynx Vault gives the same designators and values for a later board, with two extra positions.[2] For the Lynx II, which uses a different board and different designators, see the Atari Lynx II Capacitor Replacement Guide.

The Atari Lynx Vault calls a recap a must-do job on any Lynx, especially one with display faults or low speaker volume.[3] The same site recommends replacing the power-circuit MOSFET and zener before a newly acquired Lynx is switched on, because their failure puts 9 V into the processor. Do both jobs at the same sitting; the procedure is on the Atari Lynx Troubleshooting Guide.[4]

Board revisions

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The Atari Lynx Vault lists three original Lynx boards: C103949-001 Rev. 1, C103949-001 Rev. C and C104193-001 Rev. B. The Rev. 1 board has no C75 or C76 and has a C34 instead, rated the same as the C75 of later boards.[5] The revision is printed on the component side next to the Atari logo.

Capacitor list

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Original Lynx electrolytic capacitors
Ref Atari schematic C104019 Rev. C K-Retro map (later board) Where it sits on the schematic
C7 10 µF 6.3 V 10 µF 6.3 V Reset line, with D1 and R65
C8 1 µF 6.3 V 1 µF 50 V Audio coupling, between the DAC filter and the volume control VR2
C9 47 µF 6.3 V 47 µF 6.3 V Supply decoupling for the 74HC04 audio stage (U7), fed through R20
C10 47 µF 6.3 V 47 µF 6.3 V LM386 amplifier, pin 7
C11 220 µF 6.3 V 220 µF 6.3 V LM386 output coupling to the speaker and headphone jack
C19 2.2 µF 50 V 2.2 µF 50 V LCD drive circuit, beside Q6 and Q7
C20 2.2 µF 50 V 2.2 µF 50 V LCD drive circuit, beside Q6 and Q7
C23 10 µF 35 V 10 µF 35 V LCD bias circuit around Q9
C25 10 µF 6.3 V 10 µF 6.3 V LCD bias, VD2/VM lines (TP25, TP24)
C26 10 µF 6.3 V 10 µF 6.3 V LCD bias, VD2/VM lines (TP25, TP24)
C29 10 µF 35 V 10 µF 35 V +20 V supply at TP12, from the backlight inverter
C34 1 µF 50 V not listed ON button circuit, with R2 (Rev. 1 boards; see C75)
C38 100 µF 25 V 100 µF 35 V Unregulated input to the switching regulator
C39 470 µF 10 V 470 µF 10 V Regulated +5 V output, after L6 and D14
C42 10 µF 6.3 V 10 µF 6.3 V Cartridge supply, connector pin 33
C75 not on schematic 1 µF 50 V Later boards only; replaces C34
C76 not on schematic 47 µF 6.3 V Later boards only; under the RF shield near Mikey

The values come from the schematic,[1] and the third column is K-Retro's map as published by the Atari Lynx Vault.[2] Igor Kromin's picking list from 2017, built from the capacitor lists then online, gives the same quantities.[6] The two sources disagree in two places. Atari prints C8 as a 6.3 V part where the kit uses 50 V, and C38 as 25 V where the kit uses 35 V. A higher rating does no harm if the part fits. The Vault also notes that some Lynx I boards carry a 63 V part in the 2.2 µF positions and that 50 V is enough there.[2]

C38 sits on the unregulated supply from the batteries or the 9 V adaptor, so do not fit anything rated below the 25 V on Atari's schematic in that position.[1]

Procedure

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See Recommended Tools for equipment and Capacitor Failure Symptoms for what a failed part looks like.

  1. Remove the batteries. Undo the four Phillips screws on the back: the two on the left are longer than the two on the right.[7]
  2. Lift the back of the case like a clamshell, nearest edge first. Desolder the two battery wires from the main board.[7]
  3. Lift the board out of the front case. The speaker comes out with it. Watch for the button pads, which tend to stick to the board.[7]
  4. Note the polarity mark printed beside each capacitor before removing it, and work one position at a time.
  5. Leave about 3 mm of lead above the board on each new capacitor so it can be bent to lie flat and clear the case.[2]
  6. Clean off the flux, check the joints, and refit the battery wires before reassembly.

After the recap

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The Atari Lynx Vault's dead or alive test uses C39 as its power entry point on the original Lynx: 5 V applied across C39 runs the board with the switching regulator bypassed. It warns that more than 5 V at that point destroys the processor and other chips.[8] With the regulator in circuit, the same capacitor is on the +5 V rail that Atari's schematic marks at TP15, so a reading across C39 with the Lynx switched on is a quick check of the regulator output.[1]

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References

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  1. ↑ 1.0 1.1 1.2 1.3 Atari Corporation, Schematic Diagram, Handy Game (FCC), drawing C104019 Rev. C (document stamp 11 March 1992). Electrolytic values and positions read from the drawing. Hosted here as File:Atari Lynx schematic C104019 Rev C.png.
  2. ↑ 2.0 2.1 2.2 2.3 Atari Lynx Vault, "Atari Lynx Capacitor Maps" (changed 4 October 2023): K-Retro's Lynx 1 component map and picking list, with the note on C75, C76 and C34 and the advice on lead length. Vendor-published community source, CC BY-NC-SA 4.0.
  3. ↑ Atari Lynx Vault, "Atari Lynx Hardware Mods" (changed 9 October 2023), "Capacitor Replacements / Recapping". Community source.
  4. ↑ Atari Lynx Vault, "Replacing the MOSFET and zener diodes in an Atari Lynx" (changed 4 October 2023). Community source.
  5. ↑ Atari Lynx Vault, "Atari Lynx Motherboard Revisions" (changed 24 September 2023). Community source.
  6. ↑ Igor Kromin, "Picking lists for Atari Lynx capacitor replacement kits", 14 July 2017. Personal blog.
  7. ↑ 7.0 7.1 7.2 Atari Lynx Vault, "Lynx 1 disassembly steps and Screw size chart" (changed 5 October 2023). Community source.
  8. ↑ Atari Lynx Vault, "Atari Lynx Dead/Alive Test - Bypassing The Atari Lynx 9V" (changed 6 November 2023). Community source.


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