about mac plus

i baught an old APPLE - MAC PLUS computer . i pluged it to 230 v ac . nothing happened . so i opened the cover . i saw the fuse inside it had burst . so i changed a onw 5 amp fuse . and i powdered it ON . i saw spark of fire in POWDER/SWEEP board . and again the new fuse had burst . i think some component had burst too. so please give me an idea to repaire it . OR give me the circuit ,so that i can verify it...

Isn't 5A a bit large for the fuse? You may have caused further damage by installing too large a fuse.

These are not difficult machines to work on, just use standard switchmode power supply troubleshooting procedures to track down defective components. You likely have a shorted rectifier or chopper transistor on the input side of the power supply. They're notorious for cooking flyback transformers as well.

Are you sure it was a 230 volt model? If it had been imported from the U.S. it was 120 volt only.

Look for Larry Pina's book "Macintosh Upgrade and Repair Secrets".

Where are you, I can lend you the tools and books, but I expect you are not nearyby.

Geoff.

The power supply is very close to what's inside the Apple II, so find the schematic (it was in the Apple II manuals) and you have a good start.

Of course, this is assuming the power supply is the problem. SOmething further on could be at fault, straining the power supply and blowing the fuse.

Michael

If you have, or know where I can get one of the flybacks for these that would be cool, I realized I have a 512 kicking around with a bad one, last one I bought was over a decade ago and the place is out of business now.

Many years since I used to fix these.

But some ideas, BP cap on the video,LM??? chip in the video, GI??? diode in the video, Mis-jumped 120v, dead EHT ,(the little ones would blow, and were replaced by a physically larger unit that was also used in the SE which lasted.These faults were so common that you could buy kits of parts to fix them for the 128k,512k,plus and SE, of which I am sure I still have a few.

regards Andrew

The SE flyback transformer also had a built in drain to remove any remaining charge on the CRT anode.

Geoff.