Re: GS Power Supply: Warning signal?

[dalloff@freenet.columbus.oh.us (Dave Althoff)]

Rubywand (rubywand@swbell.net) wrote:
: Dave Althoff writes ...
: > 
: > Just wanted to relate my experience with GS power supply failures on
: > upgraded ROM 00 GSes.  My GS at work is a ROM 00 upgraded to a ROM 01.  It
: > is now on its third power supply
: > 
: > ....
: > Anyway, I have noticed what seems to be a warning signal when the power
: > supply is about to die. ....
: >
: > It seems that when the power supply is about to go, the crackling becomes
: > more frequent and more pronounced. .... Then, when I returned a bit later, 
: > the supply was dead. In fact, I cracked the thing open and there is this 
: > nice crunchy ceramic cap, and a couple of clearly overheated spots on the 
: > board.

:      Thanks for the info.

:      Your GS seems to be eating power supplies. Ours is a Woz ROM-00 machine 
: (one of the first three purchased in Houston) which went through the ROM-01 
: upgrade and a few motherboard swaps. It is still on the original (no 
: internal fan) power supply, except that, before adding a Zip-GSx accelerator, 
: 4MB RAM, etc., we fattened-up the PS leads.

Hmmm...I should give a little more of the provenance of this machine...
ca. 1986:  Installed in public computer lab
ca. 1991:  Public lab dismantled...system moves to my office...first PS goes
           flaky.  It never died, but the +12v dropped to well below spec
           so that the disk drive wouldn't work.  The audio circuits also
           crackled (the crackling comes from the speaker, not the PS).  That
           PS was replaced with the on-hand spare.
Last Week: Power supply fails while I am not looking.

:      If there is something odd about the line voltage at your workplace-- 
: like it is too low or too high and/or you get frequent surges-- you may want 
: to get an UPS. Otherwise, the thin leads on your power supply could be 
: contributing to instability, over-currents, and failure.

Hmmm...Well, power here isn't exactly clean...

:      You mention finding a "nice crunchy ceramic cap". Are you sure it was a 
: cap?

:      A common failure point on Apple II supplies is a capacitor-looking thing 
: called a "globar". It is a disc-shaped resistance element which is in series 
: with the AC line input. When power is turned ON, the globar is cold and has a 
: resistance of, very roughly, 50 Ohms. A second or so after turn-ON, it has 
: heated up and its resistance drops to just a few Ohms. The idea is to limit 
: initial surge voltages.

Interesting.  This would be the little round blue gizmo connected directly
to the AC power switch, right?  Not the obviously-cooked component.  That
would be this itty bitty beige cap foreward (away from the power switch) of
the TO-220 heat-sink (not sure if that is a transistor or a regulator...I
haven't cross-referenced the part number yet) and just aft of the transformer.

:      Anyway, try beefing-up the +5V, +12V, and one GND lead to #10 or #12 
: gauge. This may help save your present power supply.

Hmmm...Perhaps I'll try that.  Along the same lines...anyone have a parts
list for the GS supply...I could probably repair the old one, perhaps even
beef it up a little...

--Dave Althoff, ][.
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