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Mattel Aquarius II Capacitor Replacement Guide

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Aquarius II catalogue page (1983)
The Aquarius II in Mattel's 1983 catalogue (Mattel; used to identify the product).

The electrolytic capacitors in the Mattel Aquarius II. Sean Harrington replaced every electrolytic capacitor on the main board of his Aquarius II, together with the 5 V and 12 V regulators, but did not publish their values or positions, and no parts list or schematic of the Aquarius II board has been published.[1]

What is known

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  • The main board has separate 5 V and 12 V regulators.[1]
  • The power supply is external, on a cord that unplugs from the computer.[2][1]
  • Some models have an RGB-to-SCART video board as well as the main board.[1][3]
  • The rest of the circuit follows the Aquarius: the same processor, ROM contents, character set and ports.[2][4]

The original Mattel Aquarius has eight electrolytic capacitors: 10,000 µF 16 V and 1,000 µF 25 V reservoirs, 47 µF 10 V on the +5 V output, 10 µF parts on the +12 V and −12 V lines and in the cassette output, and small values in the reset and cassette input circuits. They are listed with their circuit positions on the Mattel Aquarius Capacitor Replacement Guide.[5] The Aquarius II board is not the same: its +12 V comes from a regulator where the Aquarius uses a discrete transistor regulator, and its power cord unplugs from the case.[1][6][2] Use the Aquarius list only to recognise which part of the circuit a capacitor belongs to, never as a parts list for the Aquarius II.

Recording your own board

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Before removing anything:

  1. Photograph both sides of the main board and, if fitted, the SCART board, square-on and in good light.
  2. Number each electrolytic on the photographs. For each, write down the printed capacitance, voltage rating, temperature rating, maker and series, whether it is radial or axial, and which pad is marked positive on the board or on the part.
  3. Note any silkscreen designators beside the parts. Harrington added his own designators when he recreated the Aquarius board, so do not expect the Aquarius board's numbering to match.[7]
  4. Identify the 5 V and 12 V regulators and note which capacitors sit at their inputs and outputs. These are the parts that matter most to the machine's power.
  5. Look for any capacitor on a negative supply line. On the Aquarius, the −12 V line's capacitor has its positive lead to ground; check the polarity marking on the board before fitting a replacement.[6]
  6. Measure each capacitor's capacitance and ESR once it is out, and keep the readings with your notes.

Replacement procedure

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  1. Unplug the power supply from the computer and from the mains.
  2. Open the case and lift out the main board, photographing each step.
  3. If the board is covered by an RF shield, find out how it is fixed before lifting it. On the Aquarius the shield is soldered at several points as well as twist-locked, and a pad can tear if a joint is not fully cleared.[8]
  4. Replace the capacitors one at a time with the same capacitance and the same or a higher voltage rating, matching the polarity you recorded.
  5. If you replace the regulators as well, as Harrington did, use parts with the same pinout and output voltage.[1]
  6. Reassemble and check the outputs of the 5 V and 12 V regulators before plugging in cartridges or peripherals.

Checks after recapping

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After the recap
Check Expected Source
5 V regulator output +5 V [1]
12 V regulator output +12 V [1]
Power-on Extended BASIC start-up; 1,652 bytes free without the 16 KB cartridge [9]

These are nominal values; no tolerances have been published for the Aquarius II.

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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 Sean P. Harrington, "Aquarius II Computer", Get Your 8-Bit On! (retrieved 2026-10-19): on the motherboard of his Aquarius II "the electrolytic capacitors were replaced, and the 5v and 12v regulators were updated to modern, switched versions"; the unit came without a power supply; RGB-to-SCART video board in some models; documentation on the Aquarius II has been thin.
  2. ↑ 2.0 2.1 2.2 M. van der Steenoven, "Mattel Aquarius II" (retrieved 2026-10-19): the power cord can be disconnected from the system; same processor, RAM and character set as the Aquarius; same rear interfaces.
  3. ↑ Leyco France advertisement, Micro 7 no. 22, December 1984, Internet Archive copy (retrieved 2026-10-19): SCART (Péritel) connection in SECAM.
  4. ↑ MAME source, src/mame/mattel/aquarius.cpp at commit eee415b (retrieved 2026-10-19): the Aquarius II's 8 KB BASIC ROM is the same as the Aquarius S2, and its character ROM is the Aquarius's.
  5. ↑ Sean P. Harrington and Mack Wharton, Aquarius Motherboard 1-1-0, bill of materials v1-1-0d (GitHub, retrieved 2026-10-19): the eight electrolytic capacitors of the original Aquarius NTSC board.
  6. ↑ 6.0 6.1 Sean P. Harrington and Mack Wharton, Aquarius Motherboard v1-1-0 Rev D schematic (the Aquarius, not the Aquarius II), 30 April 2022, hosted here as File:Aquarius Motherboard v1-1-0 Rev D Schematic.pdf: +12 V from transistor Q4 with zener ZD1; C13 on the −12 V line has its positive terminal to ground.
  7. ↑ Sean P. Harrington and Mack Wharton, Aquarius Motherboard 1-1-0, README (GitHub, retrieved 2026-10-19): silkscreen added to the recreation with all components identified, and components renumbered.
  8. ↑ Leaded Solder, "Mattel's Little Friend", 1 August 2023 (retrieved 2026-10-19): on the Aquarius, the RF shield is soldered to the board in places as well as twist-locked; a corner pad tore during removal.
  9. ↑ Kathleen Peel, "Review: Aquarius II", Your Computer, April 1984, pp. 64-65 and 67, Internet Archive copy (retrieved 2026-10-19): 4K leaving 1,652 bytes free; Extended BASIC.


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