Re: Need help with AppleIIGS

[Rubywand <rubywand@swbell.net>]

Brookie Stein writes ...
> 
> Hello,
>         I have an AppleIIGS, I'm pretty sure it has Rom 3. I've had it for a
> long time (it's not recently purchased), and it used to work fine. Now,
> I can almost never turn it on. 
 ....
> Sometimes, when the light is
> very bright, the computer actually boots up, for about 3 seconds, and
> the little beep even ... beeps, but after that the machine hums and
> crackles off.
 ....
>         Obviously, it's a power problem. I'd assume it would be in the
> rectangular silver box inside the computer, but my question is: Is there
> anyway to fix my problem? I've heard (or read, I don't remember) that
> the power supply (I think that's what the box is, right?) has a
> performance expectancy of 2-6 years.
 ....

     Depends. There is a flaw in the design of the IIgs power supply
which does appear to shorten its life-- the +5V, +12V, and GND leads are
too skimpy. As long as you stick with a bare bones system, the odds a
pretty good that your PS will be okay. Once you start expanding RAM,
adding diskette drives, and plugging in Slot cards for an Accelerator,
Hard Disk interface, ..., the additional current demand produces
significant voltage drops and noise glitching across the leads.
Evidently, the noise glitches mess up the PS feedback signal and
excessive current is drawn which damages one or more components.

     Based upon similar problems with II+ and IIe power supplies, a good
suspect for failure seems to be a capacitor associated with the PS
control circuitry ...


>>

From: O Aaland

012- My Apple IIe fails to turn on! I have to turn its power
     switch on and off several times and sometimes wait a long
     time before it finally powers up!

     If the power supply you are working on is an ASTEC brand the most
common problem is the 10V 220 uf capacitor located about 1 inch to the
rear and left of the transformer. I find this to be the cause in about
80 pecent of the ones I repair. Use a 25V 220uf capacitor as a
replacement and chances are real good that it will not fail again.

----------------------------


From: Stephen Shaw

     If you open the power supply up (WITH THE MAINS PLUG OUT!) you will
find a capacitor C7 near the transformer in the middle of the printed
circuit board (a 220 uF 16V capacitor if I remember correctly) change it
for a 220uF 25V 85 degree Centigrade rated capacitor and it should clear
the problem up.

----------------------------


From: Jeff Allen

     I've been trying to fix several dead Apple II power supplies from a
local school and have managed to bring back one from the dead now. The
fix was to replace the 10V, 220uF electrolytic cap with a new one. (I
used a 35V piece). Assuming that the board markings are useful, this was
C7, on an Astec board with the datecode "T8312" on it. I'm curious if
anyone else that has replaced that cap has noticed any browning of the
pc board where the leads enter from that 27ohm 2W 'R4' beast. ....

<<


     Other suspects include the set of larger capacitors near the AC
input side and/or a cracked 'glowbar' resistor element-- a black disk
thing near the point at which AC power comes into the board.

     Since your PS seems close to functioning correctly, one of the
fixes mentioned above may do the trick.

     For the longer term, it is a good idea to fatten up the +5V, +12V,
and GND leads. We did this several years ago when an accelerator board
was added and our original (1986) IIgs power supply is still going
strong. (For info on fattening the leads and other PS stuff, see the
Csa2Power.txt FAQs file on Ground at
ftp://ground.ecn.uiowa.edu/2/apple2/Faqs .)


> The board was slightly brown in some areas, so I'm
> thinking it probably is partially burned out.

     Some browning is normal. Usually it means that a nearby resistor
gets hot. Replacing the resistor with a bigger version of the same
value-- like swapping in a 5 or 10 Watt resistor for a 2 Watt resistor--
should eliminate the hot spot.


> I probably won't go to the
> trouble of buying a new power-thingy (50 bucks I think)
 ....

     Probably, a good choice. The "heavy duty Apple II" replacement
power supplies do not seem to offer significantly heavier leads. We got
one when our II+ PS bombed back in the early 80's-- we had installed an
accelerator board-- and, after a few years of noisy operation, it had to
be replaced.

     What worked for the II+ was a nice compact PS pulled from an old
'portable' PC. It was necessary to install an ON/OFF switch and power
cord socket on a panel in the back of the II+ and, of course, a few new
holes had to be drilled to mount the PS board. This time, too, we made
sure to use heavy leads to connect the PS to the II+ motherboard.

     There are piles of good power supplies listed at low prices in
surplus electronic parts catalogs. (See the Vendors listing included in
the "Main Hall" FAQs file.)  For around $20 you can find one which will
power a GS and which can be fitted inside the case. Still, fitting a new
PS can be a fair bit of work. Quite a few users have gotten one of the
external Buggie Power Supplies and seem very satisfied with the results.



Rubywand