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Atari ST Book LCD Board Repair

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Atari ST Book
An Atari ST Book open. The LCD panel has its own small circuit board inside the lid, behind the back cover.

The Atari ST Book display is an Epson ECM-A0572 panel with its own small circuit board, which carries electrolytic capacitors that leak with age. A weak picture, with bars or vertical lines that no contrast setting clears, is the usual result.[1][2] Robert Tercsi found that replacing the capacitors was not enough on one machine: the leaked electrolyte had also damaged two of the small surface-mount resistors that feed the C324G amplifier on the board.[1] AndresPlazaR found a second fault on his: one of the two 74HC365 buffers on the panel board had failed, so that the bottom half of the screen showed only alternate pairs of columns.[2]

The panel is driven as two halves, the top from the data lines UD0 to UD3 and the bottom from LD0 to LD3, so a fault confined to one half points at that half's data path.[2][3]

Symptoms

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  • A weak picture, with areas that no contrast setting makes fully visible.[1]
  • Bars or vertical lines through the picture.[1][2]
  • The bottom half of the screen shows only every other pair of columns.[2]
  • Brown residue on the back of the LCD glass.[2]

See also the Atari ST Book Troubleshooting Guide and the Atari ST Book Capacitor Replacement Guide.

Safety

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Unplug the adaptor and remove the battery pack first.[4] The flux or glue that holds the old capacitors gives off irritating fumes when heated: work with ventilation.[1] Protect the board around the work with Kapton tape; C2 and C3 sit close to the edge of the board, next to sensitive lines.[1] The LCD glass is fragile.

Tools and parts

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  • A plastic opening tool for the lid's back cover.[2]
  • A fine-tipped soldering iron, desoldering braid, fine wire cutters and Kapton tape.[1]
  • A hot-air rework station, if a 74HC365 has to be replaced.[2]
  • Isopropyl alcohol and cotton swabs.[2]
  • An oscilloscope, to compare a buffer's inputs and outputs.[2]
Replacement capacitors for the LCD panel board
Value Quantity
22 µF 16 V 4
10 µF 16 V 1
4.7 µF 50 V 1

Source: Robert Tercsi; AndresPlazaR bought the same values.[1][2] The original capacitors are leaded parts with their leads bent so that they lie flat; Robert Tercsi used leaded replacements because the surface-mount parts he had were taller, and AndresPlazaR found surface-mount parts about half a millimetre taller than leaded ones laid on their side.[1][2]

Procedure

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Open the lid

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  1. Close the lid support and the screen, so that the back cover can come away once its tabs are free.[2]
  2. Starting from either side of the lid's lock, separate the plastic tabs along the edge of the back cover with a plastic tool, and lift the cover off.[2]

Replace the capacitors

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  1. Cover the board around the capacitors with Kapton tape, especially near C2 and C3 at the board's edge.[1]
  2. Start with the 4.7 µF capacitor, the easiest to reach.[1]
  3. Cut each old capacitor's leads with fine wire cutters as far from the pads as possible; Robert Tercsi chose to damage the capacitor's body and spare the board.[1]
  4. Lift the remaining leads off the pads with the soldering iron, without stressing the pads.[1]
  5. Clean the old solder and residue off the pads with the iron and braid.[1]
  6. Fit each new capacitor with the polarity of the old one, bending its leads so that the body rests on the board and does not hang from the pads.[1]
  7. Support the new capacitors with a little tape or glue.[1]

Clean the glass

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  1. Disconnect the ribbon cable between the screen and the panel board.[2]
  2. Remove the metal frame that holds the screen to the plastic frame, and lift the LCD out carefully.[2]
  3. Lift the clear protective layer on the back and clean any brown residue with isopropyl alcohol on a cotton swab.[2]

Check the resistors to the C324G

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  1. Inspect the four 4.7 Ω surface-mount resistors around C2 and C3, which feed the C324G amplifier.[1]
  2. Clean corrosion carefully, and replace any resistor that is damaged or loose on its pad.[1]

Half-screen faults: the 74HC365 buffers

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  1. If only the bottom half of the screen is faulty, compare the input and output of IC2, the 74HC365 that carries LD0 to LD3, on an oscilloscope. Each output should match its input.[2]
  2. If they differ, protect the area with Kapton tape and remove IC2 with hot air.[2]
  3. Clean the pads and fit a new 74HC365.[2]
  4. If only the top half is faulty, do the same for IC3, the unlabelled IC above the JP1 label.[2]

Reassemble

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  1. Refit the LCD in its frame and reconnect its ribbon.[2]
  2. Clip the back cover back on.

Testing

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  1. Switch on and work the contrast control through its range; the whole picture should reach full strength.[1]
  2. Check that both halves of the screen show every column.[2]
  3. Check that the bars and vertical lines have gone.[2]
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References

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  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 Robert Tercsi (Robson), "STBook Display repair", tercsirobi (Google Sites), 5 April 2021: weak display with bars; leaked electrolytics on the LCD board; replacement values 22 µF 16 V (4), 10 µF 16 V (1) and 4.7 µF 50 V (1); removing the old capacitors by cutting their leads; Kapton tape around C2 and C3; the four 4.7 Ω resistors that feed the C324G amplifier.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 2.20 2.21 2.22 2.23 AndresPlazaR and others, "Repairing a ST Book.", exxosforum.co.uk, from 12 July 2024 (pages 1 to 4): the machine that starts only after the reset button is pressed; the flat internal backup battery replaced with a holder for two ML2016 cells; the leaking Conner drive replaced with a CompactFlash card on a 2.5-inch IDE adaptor; four bombs from a missing disk or a corrupted TOS chip; the LCD panel Epson ECM-A0572, its capacitors, the residue on the glass and the 74HC365 buffers IC2 and IC3; partitioning with BOOKFMT.PRG from drive P:; a 512 MB card working where a 4 GB card failed; C100 replaced to cure the reset fault.
  3. ↑ Atari Corporation, ATARI STBook Hardware Specification, 10 September 1992, section 3.3, the LCD controller: the panel is an upper and a lower panel driven in parallel (PDF pp. 7–8). Hosted here: Atari STBook Hardware Specification (PDF).
  4. ↑ Robert Tercsi (Robson), "STBook disassembly", tercsirobi (Google Sites): tools; steps 1 to 8 (disconnect power and pack; trackpad; keyboard and TOS chip; top and screen, with two screws at the back, three inside and four tabs by the battery; disconnecting the ribbons; lifting the main board out past the volume and contrast controls; the hard disk; the screen); reassembly.


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