Re: help diagnosing an Apple IIe, please.

adric22 wrote:
I just opened up the power supply. None of the capacitors appear to
be blown, but I know sometimes just old-age will get them. Are there
any particular ones that are more prone to failing than others? There
are quite a few in there and it would take a while to replace them
all.

The prime suspects are the (usually two) higher voltage electrolytics
near the power connector. When they lose capacitance, the power to the
switcher is decreased to the point where it cannot maintain regulation.

You can diagnose them by paralleling both with a pair of similar
capacitors prior to desoldering the old ones and replacing them.

The voltage rating should be as high or higher and the capacitance
rating should be equal to as much as 50% higher.

-michael

******** Note new website URL ********

NadaNet and AppleCrate II for Apple II parallel computing!
Home page: http://home.comcast.net/~mjmahon/

"The wastebasket is our most important design
tool--and it's seriously underused."
.

Relevant Pages

  • Re: Tantalum cap failures
    ... out and slowly losing capacitance, it's easy in most cases to just grossly overkill on capacitance and voltage rating and buy reliability that way. ... I also like their ECH and ECHU series when film caps are called for. ...
    (sci.electronics.design)
  • Re: Replace cap11 on Rottendog board....
    ... All I can find are 15,000 uF Caps. ... changing their capacitance value would have a significant ... effect on the functioning of the timed circuit. ... Keeping the voltage rating as high or higher is always good advice. ...
    (rec.games.pinball)
  • Re: 5.5V @ 0.33F enough for a memory cap?
    ... The standard is a 1.0f which has roughly 3 times the capacitance of ... The voltage rating on a cap specifies its *maximum* working voltage. ... having a cap rated at a higher voltage isn't a problem. ...
    (rec.games.pinball)
  • Re: Variable Capacitors used in a phase converter
    ... I wasn't assuming that this is the primary capacitance and so that's ... Volts rating is for this? ... power distribution lines. ... you *do* exceed the voltage rating and thus precipitate a breakdown. ...
    (rec.crafts.metalworking)
Loading