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Atari ST Book Capacitor Replacement Guide

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Atari ST Book

Capacitor replacement in the Atari ST Book. Atari's schematic, drawing C104446-001 Rev 7.0, gives a value and voltage for every electrolytic it shows,[1] but no populated parts list for the ST Book is known, so the list below is the schematic's and should be checked against the board. Owners report that boards of the same revision were built with surface-mount electrolytics on some machines and through-hole parts on others, and that the LCD panel's own board, which the schematic does not cover, has electrolytics that leak.[2]

Signs of failure

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  • A weak picture or vertical lines on the display: leaked electrolytics on the LCD panel board.[2]
  • The power LED lights but the screen stays blank until the reset button is pressed: on one machine this was cured by replacing C100.[2]
  • Residue around capacitor bodies, or a brown film on the back of the LCD glass.[2]

See Capacitor Failure Symptoms for the general signs.

Main board electrolytics

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Electrolytic capacitors on Atari's schematic C104446-001 Rev 7.0
Position Value Voltage Circuit Sheet
C100 10 µF 16 V Reset and power-on timing, LM555 U104 2
C102 22 µF 6.3 V LM555 U104 timing 2
C231 10 µF 16 V RS-232 driver MAX241 U206, V+ output; positive terminal to V+ 3
C232 10 µF 16 V RS-232 driver MAX241 U206, V− output; positive terminal to ground 3
C233 4.7 µF 25 V RS-232 driver MAX241 U206 3
C234 4.7 µF 25 V RS-232 driver MAX241 U206 3
C235 47 µF 6.3 V Audio amplifier LM386 U212, output to speaker connector J205 3
C236 10 µF 16 V Audio amplifier LM386 U212 3
C240 1 µF 50 V Volume control to LM386 U212 input 3
C805 100 µF 6.3 V Backup supply VBAK 9
CE1005 1 µF 50 V LCD contrast control 9
CE1006 1 µF 50 V LCD bias circuit, MAX634 U1004 9
CE1007 330 µF 25 V LCD bias output; positive terminal to ground 9
C909 330 µF 25 V Common power source, input to both converters 10
C904 1000 µF 6.3 V VCC converter U904 output; marked HFQ 10
C914 1000 µF 6.3 V Hard-disk motor converter U905 output; marked HFQ 10

Source: Atari's schematic, sheets 2, 3, 9 and 10.[1] Sheets 4 to 8, 11 and 12 show no electrolytics. The backup battery on sheet 9 is drawn as 6.0 V; one restorer replaced it with a holder for two ML2016 rechargeable cells.[1][2]

Voltage ratings

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The ratings are not uniformly low. C909 sits on the common power source, which Atari specifies at 8 to 20 V and which the 16 V adaptor feeds,[3][4] and CE1007 holds the LCD bias, which Atari's specification gives as −12 to −17 V in its supply table and −12 to −16 V in its description of the bias regulator.[3] Both are 25 V parts on the schematic. Never fit a lower voltage rating than the schematic shows.

CE1007 and C232 smooth negative supplies, the LCD bias and the MAX241's V− output, so their positive terminals go to ground. C231 sits between VCC and the MAX241's V+ output, with its positive terminal on V+.[1]

LCD panel board

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The LCD panel (an Epson ECM-A0572, according to one restorer) has its own small board with electrolytics, which leak. One restorer replaced six, cutting the old capacitors' legs close to the body and then removing the legs from the pads, and cleaned residue from the back of the glass with isopropyl alcohol. Surface-mount replacements were about half a millimetre taller than through-hole parts laid on their sides, so he used through-hole parts.[2] Atari's schematic does not cover this board.[1]

Procedure

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  1. Remove the battery pack and disconnect the adaptor.
  2. Photograph the board before removing anything and note the polarity of every electrolytic, including C232 and CE1007.
  3. On surface-mount parts, heat both pads together with hot air at low airflow and lift the part, or cut it away and remove the legs separately. On through-hole parts, take care with the pads: one lifted under C232 during removal.[2]
  4. Clean the pads and check the traces under each part for corrosion.
  5. Fit 105 °C parts of the same value and at least the same voltage rating, in a package that fits under the case.
  6. Check VCC, MTR and the LCD bias for shorts to ground before powering up.

Checks after recapping

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  • VCC and MTR: 5 V ±1%.[3]
  • LCD bias: −12 to −16 V, adjustable with the contrast control (Atari's supply table allows down to −17 V).[3]
  • The power LED should go green on a charged pack or the adaptor; yellow means the common power source is between 8.8 V and 7.2 V, and red that it is below 7.2 V.[3]

The Atari ST Book Troubleshooting Guide gives the full supply table.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 Atari Corporation, Schematic Diagram MAXIST, drawing C104446-001 Rev 7.0, twelve sheets (index dated 18 March 1992): sheet 2 (C100, C102), sheet 3 (C231–C236, C240), sheet 9 (C805, CE1005–CE1007, backup battery), sheet 10 (C904, C909, C914). Hosted here: File:Atari STBook Schematic Rev 7.0 C104446-001.pdf.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Thread "Repairing a ST Book.", exxos forum, posts by AndresPlazaR and DrJansen, 14 July to 21 September 2024, https://www.exxosforum.co.uk/forum/viewtopic.php?t=7118 (pages 2 to 4, retrieved 2026-10-01).
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Atari Corporation, ATARI STBook Hardware Specification, 10 September 1992, section 10, "Power Supply". Hosted here: File:Atari STBook Hardware Specification.pdf.
  4. ↑ "Leichtgewicht: Das ST BOOK", atari-computermuseum.de, last edited 25 August 2024, https://www.atari-computermuseum.de/nst.htm (retrieved 2026-10-01). Source for the adaptor rating.


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