The A4 is a temperamental beast, and keeping them going can be a hard job at times. This is a list of faults I and others have managed to fix.
Machine runs fine from battery, and battery is charged, but is unable to
run on mains power. When in mains power mode without battery, screen and
floppy drive make a fluttering sound.
This is due to the machine being powered off the charging supply, which oscillates from 12-14V. The machine will work at 14V, but not at 12V so each cycle is a periodic power up and shut down. Check the two large SMD Schottky diodes (SOT89 package I think) in the middle of the rear side of the board, and one on the front side. Replace as necessary (1A 30V Schottky).
Machine won't run from battery, but battery is still charged.
Andre says this is usually due to installing a shorted battery or one with a contact shorted to the internal diodes. He says this can be fixed by replacing the two fusible resistors under the hard disc (0.33 ohms, 0.5W).
Philip Pemberton adds:
Machine power flutters with battery removed. Battery will not charge when AC adapter is connected and machine is powered up - battery LED flashes green (battery error). If battery is removed, power "flutters" rapidly.
Power supply output inoperative. Machine is running from the current-limited battery charge supply (12V).
Open power supply cover, remove PSU circuit board. Replace the 50V 1uF electrolytic capacitor near power inlet (on left side of PCB when viewed with the mains inlet connector facing AWAY from you). It may be necessary to move the mains filter capacitor (black sleeved object, about 1" by 0.75" with two wires). The capacitor should be replaced with a good-quality 105 deg.C low-ESR capacitor, e.g. Matsushita-Panasonic NHG (ECA-HG) series. Note that the case plastic may be brittle. Be careful when removing the screws, then cover the screw-posts with a fairly thick layer of five-minute epoxy (e.g. Araldite). Leave the epoxy to set overnight. This should strengthen the posts enough to stop them shattering. Also, when tightening the screws, do not apply any pressure to the screwdriver - rotate it, but don't push down on it. Before driving the screws in, rotate them counterclockwise until you hear (or feel) a "click". Then drive the screws in fully. This should make the screws run on the original thread, rather than creating a new thread (and severely weakening the plastic).
Another thing - if you're going to replace the one capacitor, it might be worth replacing the whole lot. This should cost around £10 in parts and take around an hour. It should also significantly extend the life of the power supply.
He also adds:
Check around the glass on the LCD and make sure that no part of it is sitting on top of the L-shaped plastic guides, or you'll end up breaking the LCD when you re-fit the cover.
Page by Theo Markettos (email at theo [at@] markettos.org.uk), last modified 2005-01-13
Return to Theo's A4 pages.