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Apple Newton MessagePad Capacitor Replacement Guide

From RetroTechCollection
Power supply of the Original MessagePad (H1000) on Sharp's circuit diagram. C51 (3.3 µF 35 V) is on the +28 V output; C59 (33 µF 16 V) is at the lower left.

Polarised capacitors in the Apple Newton MessagePad family, where they fail, and how to replace them. The Original MessagePad and MessagePad 100 (both model H1000) have three small packaged electrolytics, and two of them fail often enough that owners replace them as a matter of course. For the MessagePad 2000 and 2100 the values come from Apple's prototype schematic. For the 110, 120 and 130 no capacitor values have been published.

Original MessagePad and MessagePad 100

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Sharp's service manual for the H1000 (Sharp model BO-A300) contains a circuit diagram but no parts list, and the lower edge of the scanned diagram is cut off.[1] The values below are read from that diagram and confirmed by owners who have replaced the parts.

H1000 electrolytic capacitors[1][2][3]
Ref Value Circuit Fault when it fails
C1 100 µF 4 V Speaker output Start-up chime and sounds almost inaudible
C51 3.3 µF 35 V Output of the +28 V LCD booster (IC18) Garbled, flickering display with lines and black bars
C59 33 µF 16 V Power supply, at the 47 µH coil L3 None reported

C1 and C59 are the only parts of their kind on the board: a silver cylindrical electrolytic inside a black rectangular holder. C51 is a surface-mount electrolytic on the far side of the main board.[2][3] The circuit diagram also shows C52 and C56, both 10 µF 16 V, in the power supply; no failures of them have been reported, and the diagram does not say whether they are electrolytic or tantalum.[1] Victor Rehorst, working from Frank Gründel's photographs, also suggests replacing a 470 µF 10 V capacitor at the edge of the board as a precaution, without naming its designator.[4]

Replacement

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Warning: the H1000's power circuit uses field-effect transistors that static kills easily. Work on an earthed mat with a wrist strap. Frank Gründel lost Schottky diode D11 on his first C51 repair; the unit then ran from batteries but not from the adapter until it was replaced.[2]

  1. Open the case and take out the main board as described on General Maintenance. C1 can be reached once the back of the case is off; C51 is on the other side of the board.[3]
  2. Remove C1 with two fine soldering irons, one on each lead, or cut its legs with a craft knife and unsolder each stub separately. Levering it off tears the pads away.[3]
  3. Clean the old electrolyte off the board round each position with a suitable cleaning fluid before fitting the new parts.[3]
  4. Fit replacements of the same capacitance. A higher voltage rating is fine as long as the part is no bigger than the original, or the case will not close; C51 was originally 4 mm across, and a 6.4 mm part kept the board from sitting flat. Small tantalum capacitors have worked for C51.[3][2] Observe the polarity marked on the board.
  5. Keep the soldering iron to 320 °C or less and each joint under 5 seconds, which is Sharp's limit for electrolytic capacitors on this board.[1]
  6. Test from batteries and from the adapter before closing the case.

MessagePad 110, 120 and 130

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No capacitor values have been published for these boards, and the faults reported on them are not capacitor faults. On the 130 the usual power-up and backlight failures come from a loose IC (U43) and badly made resistors; see the troubleshooting guide.[5]

MessagePad 2000 and 2100

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Sheet 11 of Apple's "Q" EVT2 schematic: the four switching supplies and their capacitors

Apple's schematic for the EVT2 prototype of the MessagePad 2000 (code name Q, "EVT2 Schematic V2.1") gives values for every capacitor.[6] It is a pre-production drawing, so check positions against your board. Connector and IC designators that owners report on production boards (J4, J5, J7, J13, U34 and the SI9712 card-slot switches) and the blown C147 reported on a 2100 all match it.[7][8][9] The drawing marks polarity but does not say whether each part is tantalum or aluminium.

Polarised capacitors on the "Q" EVT2 schematic[6]
Ref Value Sheet Where it is on the drawing
C88 0.1 F 2.5 V 1 superDvcc backup supply, fed from dVcc through R5
C61 100 µF 10 V 3 aVcc supply to the Keynes audio and tablet ASIC (U6)
C51 10 µF 6.3 V 3 Microphone supply filter after R18 (marked "10UF-NO_FUSE")
C5 100 µF 10 V 4 aVcc beside the infrared LEDs DS1 and DS2
C128 47 µF 16 V 9 Backlight inverter supply after switch Q7
C121 4.7 µF 25 V 9 Backlight inverter, at transformer T1
C140 10 µF 16 V 9 Card-slot supply rails feeding U29 and U30
C144 10 µF 16 V 9 Card-slot supply rails feeding U29 and U30
C152 47 µF 16 V 10 Main battery line after current sensor U36 (MAX471)
C147 100 µF 10 V 11 psVin, input of the +3.3 V converter U40 (MAX1651)
C139 100 µF 10 V 11 +3.3 V output
C123 100 µF 10 V 11 Input of the LCD bias converter U32 (MAX1771)
C119, C124 4.7 µF 50 V 11 +19 to +30 V LCD bias output
C153 100 µF 10 V 11 psVin, input of the +12 V converter U38 (MAX1771)
C148, C149 33 µF 20 V 11 +12 V output
C150 100 µF 10 V 11 psVin, input of the +5 V converter U34 (MAX1771)
C151, C154 100 µF 10 V 11 +5 V output

C147, C153 and C150 sit directly on psVin, the supply rail fed from the battery or the adapter, so they see whatever the adapter puts out.[6] They are rated 10 V; Apple's own adapter is rated 7.5 V.[10] C147 is one of the first parts to fail on a wrong adapter, and the same overvoltage usually kills U34; check both, and the adapter, before powering the board again.[9][11]

C88 is the backup capacitor that keeps the clock running while the batteries are out; Apple allows about an hour.[6][12] Matthias Melcher found it almost dead on a 2100 in 2026 and ordered a replacement; he describes it as easy to reach and replace.[13] Fit a part of the same capacitance and at least the same voltage rating, and check that it fits the space.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 Sharp Corporation, Service Manual, Model BO-A300 (Newton MessagePad). Hosted as File:Sharp BO-A300 Newton MessagePad Service Manual.pdf; see Sharp BO-A300 Service Manual. Circuit diagram, PDF pp. 37–38 (sheet dated 24 May 1993); soldering notes for electrolytic capacitors and coils (320 °C maximum, within 5 seconds) and electrolytic lead forming, p. 35; speaker lead soldering, p. 19.
  2. ↑ 2.0 2.1 2.2 2.3 "MessagePad 100 (OMP H1000) Flickering/glitching", NewtonTalk, October 2018: Frank Gründel's reply of 6 October [1], his follow-up of 9 October [2] and Erik Johnson's reply of 10 October [3] (MARC archive). Community repair reports. C51, 3.3 µF 35 V, surface-mount, 4 mm diameter in Erik Johnson's unit; a 5 mm part also fitted but a 6.4 mm part stopped the board sitting flat; C51 as the output capacitor of the 28 V LCD converter round IC18; C1 and C59 as the only two capacitors of their packaged type; tantalum replacements of about the original size; D11 lost to static during Frank Gründel's first C51 repair; Erik Johnson's suggestion to replace C1, C51 and perhaps the third capacitor on every H1000.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Frank Gründel, "How to fix hardware-related sound volume problems on OMPs and MP100s", NewtonTalk, 2 February 2015, MARC archive, and "Notephone and OMP/MP100 issues", 15 November 2020, [4]. Community repair reports. C1, 100 µF 4 V: location left of the white fuse, near the speaker pads, with the battery compartment towards you; silver, cylindrical, in a black rectangular holder; removal with two irons or by cutting the legs; cleaning; a higher voltage rating is acceptable if the part is no larger; C51 on the far side of the board.
  4. ↑ Victor Rehorst, reply in "Capacitor Replacements?", NewtonTalk, 6 February 2026, MARC archive. Community report: C1 100 µF 4 V for the sound and C51 3.3 µF 35 V for the display, from Frank Gründel's draft disassembly notes; tantalum parts for C51; a 470 µF 10 V capacitor on the side of the board suggested as a precaution.
  5. ↑ Frank Gründel, "MP130 Fixes", PDA-Soft, pda-soft.de (read 2 October 2026). Community repair guide: U43; resistors R73, R79, R61 and R52 (4.64 kΩ) and R112 (1.5 kΩ).
  6. ↑ 6.0 6.1 6.2 6.3 Apple Computer, schematic "Q", EVT2 Schematic V2.1 (drawing AP2375-10 on sheet 1), 12 sheets. Hosted as File:Apple MessagePad 2000 Q EVT2 schematic.pdf; see Apple MessagePad 2000 Q EVT2 Schematic. Polarised capacitors on sheets 1, 3, 4, 9, 10 and 11; C88 (0.1 F 2.5 V) on the superDvcc line on sheet 1.
  7. ↑ Frank Gründel, "How to disassemble / take apart an Apple Newton MessagePad 2000 / 2100", PDA-Soft, pda-soft.de/2x00_disassemble.html (read 2 October 2026). Community guide: connectors J4 (speaker), J5 (microphone), J7 (power switch), J9 (display) and J13 (backlight); the gold capacitor that replaces the backup battery.
  8. ↑ Frank Gründel, "The MAX1771 Problem", PDA-Soft, pda-soft.de (page dated 24 October 2011; read 2 October 2026). Community repair report: U34 (MAX1771) and an SI9712 per PC Card slot on production 2100 boards.
  9. ↑ 9.0 9.1 Frank Gründel, reply in "Tantalum caps", NewtonTalk, 26 March 2011, MARC archive. Community report: a blown C147 on a dead 2100, and C147 as one of the first parts to fail on a wrong power supply.
  10. ↑ Newton FAQ, Part II: Hardware, B7 "Which power adapters can I use?", newtonfaq.com (read 2 October 2026). The Newton 9W Power Adapter, model H0165, rated 7.5 V at 1.2 A; no more than 7.5 V from any substitute.
  11. ↑ Frank Gründel, reply in "Need Assistance With Repairing eMate 300", NewtonTalk, 1 January 2025, MARC archive. Community report: above 7.5 V a 2x00 usually loses its MAX1771.
  12. ↑ Apple Computer, MessagePad 2100 User's Manual, 1997. Hosted as File:MessagePad 2100 User's Manual (1997).pdf. Appendix A, pp. 243–245: a super capacitor as backup power; batteries out for no more than an hour.
  13. ↑ Matthias Melcher, "MP2100 repair, help needed", NewtonTalk, 23 July 2026, MARC archive. Community report: the single electrolytic supercap that keeps the time and date chip running, almost dead; easy to reach and replace.


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