PROBLEME :
Lorsque j'essaye de démarrer mon Macintosh IIcx, par le bouton Power-On du clavier ou bien via le bouton marche-arrêt, ce dernier ne donne aucun signe de vie.

EXPLICATION :
L'alimentation, de conception ASTEC, équipant ces Macintosh a tendance à développer une mauvaise connexion dans l'alimentation d'énergie résiduelle (Trickler). L'alimentation en énergie résiduelle est présente tant que le Mac est branché sur le secteur (même lorsque le Mac est "éteint"), et fournit la puissance nécessaire au démarrage par la touche "Power-On" du clavier ou par le bouton de démarrage à l'arrière du Macintosh.
Même si les circuits de l'alimentation d'énergie principale sont corrects, il suffit que le Trickler soit déffectueux pour qu'il ne puisse fournir le signal nécessaire au démarrage.

SOLUTION :
D'une façon générale, il est possible de débloquer le trickler (en débranchant le Mac pendant 20 secondes à 5 min). Cela fonctionnera mais pour une courte durée (le phénomène reprendra au bout de quelques instants). Aussi, si vous avez un Mac avec ce problème, vous pouvez commencer par le débrancher pendant un moment, et essayer ensuite de le rédémarrer par le bouton de mise sous tension. Pour régler ce problème de manière permanente, vous devrez ouvrir le bloc d'alimentation : déclipsez les deux agrafes qui maintiennent le ventilateur et retirrez le. Dévissez alors les deux vis qui tiennent la plaque métallique et enlevez-là. Enlevez maintenant la feuille isolante qui était sous la plaque. Si vous tenez l'alimentation avec le circuit imprimé vers vous et la fente de ventilateur sur le dessus, le problème se situera sur une des soudures dans le quart inférieur gauche du circuit. Refaites toutes les soudures qui se trouvent à cet endroit (faîtes attention de ne pas laissez tomber les composants du circuit imprimé lorsque vous referez les soudures).

Si les résultats ne sont pas probants, essayer ce qui suit (non traduit) :

Repairing your sluggish starting Mac IIcx, IIci, or Quadra 700 Astec Power Supply Copyright 1992 by Owen Hartnett Symptom: Macintosh IIcx, IIcx or Quadra 700 refuses to start up from either the power on key on the keyboard or the rear power switch. Cause: The unit's +5volt trickle voltage degrades to 0 volts when AC power is supplied to the unit. These model Macintosh use this 5 volt trickle voltage to power the startup circuits. This voltage is supplied while the main power (the Macintosh itself) is off but while the unit is still plugged in to the AC line. The voltage degrades variably and intermittantly making problem diagnosis difficult. The problem, however, becomes progressively worse. In it's latest stages, the line would degrade within one minute after power off. Removing the power supply from the AC line for 20 seconds to five minutes will generally permit subsequent power on attempts. Test 2: Remove the power supply from the Macintosh. Attach the negative lead of a voltmeter to the metal case of the power supply. Set the voltmeter to measure AC voltage in the 9 volt range. Measure the indicated pin from the transformer T4 for approximately 9 volts AC voltage. It is fairly easy to find T4 even on the lead side of the printed circuit board. It has 6 leads which are arranged in the pattern as shown above. There is a noticable gap on the board that contains no leads which T4 spans and which appears under the two top pins. Measure the 9 volts AC on the specified lead. The 9 volt lead has a short trace which connects to one other object (a diode) up and to the left of the transformer lead. You may find that the 9volts is there when you first apply AC power, but dissipates after a variable amount of time. If you can measure voltage on this lead considerable less than 9 volts (this author measured 0 volts) when power is supplied to the unit (but the unit is off), then you have the problem. The Repair: The fix consists of replacing three transistors, (optionally) one transformer, and adding one resistor. All the parts are on the upper board, but it is necessary to remove both the upper and lower board from the power supply. To remove the boards: Remove the power supply from the Macintosh (first unplug the AC line and monitor cord). Remove the top cover of the power supply by removing the two screws which hold it. Remove the fan by squeezing the two fingers at the bottom of the fan and lift the fan up partway. Unplug the plastic connector which connects the AC line outlet to the upper circuit board. Remove the two screws which secure the upper PC board to the power supply's metal frame. The upper PC board is permanently attached to the lower board by two wiring harnesses. Remove the three screws which hold the lower board to the metal power supply case. One screw is in the corner near the fan, one screw is located near the AC cord connector and another screw is in the middle of the board near the back. Remove the AC power receptacle unit by lifting it up and away from the metal power supply frame. On the underside of the unit, remove the plastic spacer "key" which fits between the exterior connector plug and the metal case by squeezing the middle of the key and sliding it off. The exterior connector plug is retained by two split fingered plastic finger plugs. It is necessary to squeeze these (this author used needle nosed pliars) so that the split fingers moved in opposite directions. This is the biggest pain in the neck to remove in the whole disassembly (and it's not that bad!!). Be careful not to break the split fingers, but they are fairly hardy. Once the exterior connector plug is free from the metal case, you can remove both PC boards as a unit by tilting the bottom board on its way out. You don't have to force it, there's a way to tilt it to get it out without incident. A little experimentation will show you the proper way. The Fix: According to an engineer at Astec, who was kind enough to supply me with this information, there are three parts known to give trouble in this model supply. They are transistors Q4, Q5, and Q6. There is also a modification to the supply using a resistor which is currently being done to all current versions of the supply. I also replaced the transformer T4, because I thought it might be faulty in my trials. Replacement of the three transistors alone, or the three transistors and transformer were not enough to fix the problem. It was necessary to make the modification to effect the fix. I do not think that the transformer replacement was necessary, but I ordered the part and did it anyway. I did not test the fix with the original transformer due to time constraints. Parts List: Q4, Q5: Transistor 2NP5401 Astec Part #210-11700620-0152 Q6: Transistor 2SC1213A Astec Part #209-11700690-0120 T4: Transformer Astec Part #852-00012100-7777 Modification: 1K Ohm Resistor - at least 1/6 watt (I used a 1/4 watt). The colors are Brown Black Red for this value. To fix: Replace Q4, Q5 and optionally T4. Replace Q6 but instead of inserting all three leads of the transistor through the board, only insert the middle and right leads. Leave the left lead positioned above the board and away from the other leads. Now insert the 1K Ohm resistor into the hole where the uprooted lead from Q6 would have gone. Solder the resistor in series with the remaining lead from Q6.Replace the boards in the power supply by reversing the instructions above. When replacing the fan, make certain that you put the fan connector back correctly. The ridge on the plug connector goes toward the back of the connector on the lower board. Owen Hartnett omh@cs.brown.edu OHM Software Company 98 Long Pasture Way Tiverton, RI 02878 (401) 253-9354 (If necessary, leave a message on the machine that indicates you are calling for parts.)