Power SuppliesWARNINGDanger of severe electric shock or worse.Do not operate the power supply without observing all the proper safety precautions. Do not operate with the covers removed or connected to the mains supply. If in doubt consult a qualified electrical engineer The ACT Sirius 1 comes fitted with one of two types of power supply made by different manufactures. The level of failure increases as the components age. Try to avoid long periods of power down. Power up the computer at regular intervals but avoid rapid switching on and off. COMPOWER 
Click to see larger image in new window. This is the most common power supply fitted. Should this power supply fail a large number of components will have to be replaced. Due to the low impedence of the primary circuit all components should be removed before testing. The usual components to fail are:
Transisors
Once the supply is working adjust R116 to give 5 volt output on full load. ASTEC 
Click to see larger image in new window. This power supply is slightly better than the Compower supply in respect of its higher current capability and cooler running. This power supply is fully self regulated i.e. no presets to adjust the output so voltages may vary from that specified i.e. 5 volts and 12 volts. Capacitors should be checked for leakage or bulging. There are at least two revisions of this power supply with a noticible difference a voltage regulator at IC2 is missing plus other suptle differences. This may be an earlier version. Check for dry joints around R4 27ohm 1W and other resistors near the power transistor. Dry joints round terminals of switch mode transformer (the one marked "DANGER" high voltage) Components likley to cause failure:
Transistors
A fault that is becomming increasingly common is clouds of foul smelling smoke and a cracking sound usually at power on. The first cause is C1 mains suppression capacitor. This is positioned across the input AC supply and produces the smoke as it fails. Generally this does not destroy the power supply simply replace with a 0.1uF 275Vac metallised polypropylene capacitor. It MUST be AC rated to above 275Vac. The second is C2 there may be clouds of smoke and cracking sounds although this is not always the case. Check this capacitor and if found defective replace with 0.22uF 275Vac metallised polypropylene capacitor. It MUST be AC rated to above 275Vac. Observe all precautions whilst checking or repairing this power unit. Here is the effects a capacitor failing. The capacitor is C2. This happened whilst I was checking other components in the computer. See it HERE If you have any other fixes to these power supplies or a circuit diagram to add to this page please email them for inclusion and a mention on the contributors page. Note: The information above is used at your own risk and implies no warranty as to its suitability as a repair. No responsibility can be accepted for any accidents or injuries as a result of using the information. All liability rests with you. |