MY PENTIUM 3 COMPAQ DESKPRO POWER FAIL TO START FOR KEEPING THE MACHINE OFF FOR A LONG TIME.PLEASE KINDLY HELP ME TO REPAIR.WITH CIRCUIT DIAGRAMS.
I'd assume this machine uses an ATX design power supply. ATX and other late designs (after the days of the AT style units) have a standby voltage supply which powers just a small portion of the motherboard circuitry (voltage= +5 volts). Your problem is likely caused by one or more electrolytics in this standby section. If you open the supply, you should see at least 2 switching transformers, likely sitting close to each other. One will be large (for the main/full power) and a small one (for the standby section). Usually the bad capacitor is on the primary side (on the side where the switching transistor is). It may be a 10MFD/50Volt or 47MFD/25Volt, or some value close. If the bad cap is on the secondary side (the section which is connected to your motherboard), then the value will be something like a 1000MFD/10Volt or 16Volt, or 1500MFD, 2200MFD. This capacitor will be physically larger than the one noted for the primary side. I can't tell you the exact location on the board where these capacitors might be, except they will be close to the small transformer mentioned above. If you have a digital camera, and could take a pic or 2, I might be able to point to the exact suspect part. You could send pic to [email protected]. Of course, you need a solder iron/solder, and a little skill...
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