Routine Maintenance of Atari Power Supplies?

[+Larry]

Is it necessary (or useful) to replace the large electrolytic caps inside the "repairable"-type Atari power supplies or inside the computers? Perhaps especially the 1200XL since it uses the standard AC-output power supplies? I've read before about these caps "drying out" and failing with dire Atari consequences, but I've never had any issues personally.

 

-Larry

[russg]

Is it necessary (or useful) to replace the large electrolytic caps inside the "repairable"-type Atari power supplies or inside the computers? Perhaps especially the 1200XL since it uses the standard AC-output power supplies? I've read before about these caps "drying out" and failing with dire Atari consequences, but I've never had any issues personally.

 

-Larry

I haven't run into a bad capacitor problem with old electronics. I've had 75 year old capacitors in old telephones working just fine. Old capacitors were huge and supposedly unreliable.

They used paper and aluminum foil. Modern capacitors are the size of a grape that are the same farads as the four by two inch ones in old phones.

Edited April 15, 2012 by russg

[Rybags]

One possible reason at least for the ones inside our machines - the operating voltage and current isn't very much so there's not the amount of stress when power cycling, or amount of heat (usually) vs modern PCs or most other home electronic gear - having the mains -> DC conversion outside the machine also helps a lot.

 

Also, probably most of them are for filtering purposes which I imagine is a low wear application.

[+bob1200xl]

Let me see if I can remember this right...

 

A capacitor is two conductors separated by a dielectric insulator. Its ability to hold charges depends on the dielectric properties, the area of the plates and the distance between them.

 

Old foil/paper caps are just that - foil and paper. There is very little to 'wear out' in them. There is no polarity and I can believe that they may last forever as long as the internals stay sealed.

 

Electrolytic caps have the dielectric 'grown' on the plates and have a polarity that you must observe, lest you 'un-grow' the dielectric. When used as power supply filters, high AC currents flow through the cap, generating heat and stress. This deteriorates the dielectric and reduces its effectiveness as a filter. If the cap fails, it may short, blowing a fuse, or be unable to filter out all the AC component, causing hum bars in the video and audio.

 

Neither of these will normally affect the rest of your computer, other than the fuses and perhaps the rectifiers. The dangerous failure is one where the voltage regulator shorts. This puts high voltages (>8v) on all your ICS without blowing any fuses. Whether the regulator is in an internal power supply, such as an 800/1200XL/1050, or an external supply, such as a 130XE/800XL, makes no difference. If the regulator shorts, you're going to smoke test your computer.

 

Bottom line: Electrolytics have a high failure rate but cause little damage,

 

As a side note, newer, large electrolytics usually come in higher values for the same package size. This means that you can replace a 6800/16v cap with a 10,000/25v unit. Don't get crazy with the ufd. Installing a 25,000ufd cap where you had 4,700ufd can cause current in-rush problems. Use a higher voltage unit with less than a 50% increase in ufd.

 

Bob

[+poobah]

... and older electronics often had more 'head room' on the components. Stuff you get today is often close to, if not already out of spec.