Quote:
Originally Posted by neoxide
... It sound like something's trying to start, but can't for some reason ...
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This is a standard method of failure in the IIcx, IIci and Quadra 700, which have a common power supply as well as case form. It results from change in bias voltage across a diode as a result of ageing. The result is unreliable production of the 5V TRKL supply that enables soft-power startup from the keyboard. The fault is common in the Astec power supplies, and less so in the Delta units.
Permanent cure is either replacement of the PSU, or a
repair that involves insertion of another diode in series with the out-of-spec component to increase the required bias voltage. This involves dismantling the PS, with some risk to you if you do not allow the filter capacitors to discharge before you do so.
Some people have found a temporary workaround, which is much less satisfactory than an active repair by replacement or repair, viz. to flick the
mains power switch at the wall or on a powerboard off and on again quickly while holding down the power key on the keyboard. I have found that complete removal of the power supply for several minutes also works, but is not specially convenient. Neither is the other suggested alternative of switching the
mains power switch at the wall or on a powerboard off when the Mac is not in use, and on again a few seconds before trying to start up from the keyboard. This latter is also an effective way of wasting your PRAM battery's charge while the Mac is not getting mains power. Note that these mains switch techniques are
not intended for the auto-restart-after-power-failure switch on the back of the Mac.
The eBay seller elkinfaun has sold a number of IIcx/IIci/Q700 PSUs for about AUD20 during the last several months, and is worth watching, or contacting through eBay's internal email system.
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