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Apple PowerBook Duo Dock Capacitor Replacement Guide

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The power supply, 661-1660, sits in the base under the subassembly (Apple Service Source, PDF p. 121)

The Apple PowerBook Duo Dock, Duo Dock II and Duo Dock Plus all use power supply 661-1660, and that supply is where the dock's electrolytic capacitors are.[1] Its usual failure is the "tick of death": the dock ticks when plugged in and will not power up, take a Duo or eject one.[2] Apple treats the supply as a sealed exchange part and publishes no component list for it, so the values here come from owners.[3]

Signs of failure

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  • Periodic ticking from the dock, worst after it has been unplugged. In mild cases it stops after an hour or two plugged in; later it does not stop, and a Duo inside may not eject.[2]
  • No power, a ticking supply and no raster. Apple's test is the power supply to logic board cable: pin 5 (yellow) 5 V ±0.5 V and pin 7 (blue) 20 V ±0.5 V.[3]
  • A dock that ticked and would not start in a 2017 68kMLA thread came back after a recap of the supply.[4]

See Capacitor Failure Symptoms for what failed electrolytics look like.

Power supply capacitor list

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jmacz recapped an original Duo Dock's supply in March 2025 and posted this list; the ticking stopped and the dock inserted, ran and ejected a Duo afterwards. He found no electrolytics anywhere else in the dock, and on his supply a daughterboard position that holds a surface-mount electrolytic on other units carried a tantalum.[5]

Duo Dock power supply electrolytics (jmacz, 68kMLA, community source)[5]
Positions Capacitance Voltage Temperature Size (D × H, mm)
C24, C28, C30 100 µF 25 V 85 °C 6 × 11
C6, C31 47 µF 25 V 105 °C 5 × 11
C10, C13, C35 470 µF 25 V 105 °C 10 × 20
C9, C11, C17 2200 µF 25 V 105 °C 13 × 39

Low End Mac names C28 as the usual culprit and says some supplies have the failing part at C24 instead.[2] On Byrd's supply both C24 and C28 were 100 µF 35 V parts, not the 25 V Low End Mac describes, and he replaced both; Mark97062 revived two supplies the same way.[6] Every part in jmacz's list is rated 25 V. Read the markings on your own board before ordering, because supplies differ.

The logic boards have no aluminium electrolytics on the boards jmacz and jvernet opened (an original Duo Dock and a Duo Dock II).[5][7] techknight's advice in the same Duo Dock II thread was to recap the logic board as well as the supply; check your own board.[7]

Procedure

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Warning: the supply runs from mains and its primary-side capacitors can stay charged after it is unplugged. Leave it unplugged for some time and check with a meter before touching the board.

  1. Unplug the dock, take off the cover and lift out the subassembly as on Apple PowerBook Duo Dock General Maintenance.[3]
  2. Press the two plastic latches and push the supply in at the mains inlet to free it, then lift it out of the base. Low End Mac tips the dock so the supply slides out.[3][2]
  3. Drill out the four rivets holding the two halves of the case: two on the top and two on the end.[2] Clear every chip of metal from inside the case before closing it.[4]
  4. Bend back the metal flaps and slide out the fan. Note which slot each fan lead uses and which way the fan blows before disconnecting it.[2]
  5. Work the bundle of output wires and its rubber collar out of the keyhole in the side wall.[2]
  6. Remove the three Torx screws holding the board to the case and lift the board.[2]
  7. C28 is close to the mains inlet, on the far side of a vertical board from the word "CAUTION" printed on it, in line with the letter O.[2] Replace it, and C24 if present, observing polarity; replace the rest of the list if you are recapping the whole supply.
  8. Refit the board, wires and fan. Close the case with short sheet-metal screws (Low End Mac) or aluminium pop rivets (68kMLA).[2][4]
  9. Refit the supply by hooking its cut-outs over the three tabs in the base and pushing it towards the rear panel until it latches.[3]
  10. Before closing the dock, check pin 5 and pin 7 of the power cable against Apple's limits.[3]

After the recap

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Power supply output check (Apple Service Source)[3]
Cable pin Wire Expected
5 Yellow 5 V ±0.5 V
7 Blue 20 V ±0.5 V

If the ticking has stopped but the Duo still will not draw in, check the docking mechanism next; jmacz's recapped dock still needed its lock linkage adjusting.[5] See Apple PowerBook Duo Dock Troubleshooting.

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References

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  1. ↑ Apple Computer, PowerBook Duo Dock Service Source, January 1996, Exploded View, PDF p. 121. Hosted as File:PowerBook Duo Dock Service Source.pdf. Power supply 661-1660 common to all three docks.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 Dan Knight, "The Duo Dock Tick of Death", Low End Mac, 2 September 2016, https://lowendmac.com/2016/the-duo-dock-tick-of-death/ (read 4 October 2026), adapted from Sean Cleary's Duo Dock page. Symptoms; the 100 µF capacitor at C28, or C24 on some supplies; removing the supply, drilling the four rivets, removing the fan and board; closing the case with short sheet-metal screws.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Apple Computer, PowerBook Duo Dock Service Source, Take Apart chapter, "Power Supply", PDF pp. 89–91, and Troubleshooting chapter, "Symptom Charts/Power", PDF p. 36.
  4. ↑ 4.0 4.1 4.2 68kMLA forum thread "Duo dock plus/ll", July 2017, https://68kmla.org/bb/threads/duo-dock-plus-ll.7275/ (read 4 October 2026). Ticking supply; recap cured it; rivets drilled out and replaced with aluminium pop rivets; clear the drilling swarf.
  5. ↑ 5.0 5.1 5.2 5.3 68kMLA forum thread "Powerbook Duo 280c + Accessories Maintenance", jmacz, posts of 10 and 15 March 2025, https://68kmla.org/bb/threads/powerbook-duo-280c-accessories-maintenance.49469/ (read 4 October 2026). Duo Dock power supply capacitor list by designator; no electrolytics on the logic board; result of the recap.
  6. ↑ 68kMLA forum thread "Duo Dock repair - "click of death" fixed, now GLOD!", March and April 2012, https://68kmla.org/bb/threads/duo-dock-repair-quot-click-of-death-quot-fixed-now-glod.25039/ (read 4 October 2026). 100 µF 35 V parts at C24 and C28 on one supply; two more supplies revived by the same replacement.
  7. ↑ 7.0 7.1 68kMLA forum thread "DuoDock II: crash often and now do not boot", February 2017, https://68kmla.org/bb/threads/duodock-ii-crash-often-and-now-do-not-boot.6186/ (read 4 October 2026). No can capacitors on the Duo Dock II logic board; techknight's advice to recap the supply and the logic board.


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