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17.011 Some of our classroom IIe's don't work at all. There is no beep and nothing on the monitor. Do the power supplies need to be replaced?




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This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.

17.011 Some of our classroom IIe's don't work at all. There is no beep and nothing on the monitor. Do the power supplies need to be replaced?

         Maybe not. My experience with a couple Australian Platinum //e's indicates
that you may be able to repair the power supplies.

     The power supply in the //e's I fixed is made by Dyna Comp, Inc. for
Apple, model no: 699-0136. Ratings are as follows: Input 240V/50Hz, Output +5V/
4A, +12V/1A, -5V/.25A, -12V/.25A.

     Measuring the voltages on the //e motherboard I get +5V= +1.3V, +12V=
+2.8V, -5V= -4.3V. If I disconnect the power supply connector from the
motherboard and switch it back on, I measure the correct voltages on the
connector.

     The fault is caused by one or two failed 1uF 35V 85deg small
electrolytics. The location of each is as follows:

o- 103mm (4.1") from the back, and 27mm (1") from the left of the circuit board

o- 163mm (6.4") from the back, and 10mm (0.4") from the left of the circuit
board.

I checked each of the ones I removed. they measured less than .05uF.

     The fix is to replace each capacitor with a 1uF 35V or higher rated
electrolytic-- if there is no "+" indication on the circuit board, mark the
plus side before removing the old capacitor. I used 1uF 50V 85deg as that's
what was in my parts bin. (You may need to clean up some gunk leaked onto the
board by the old capacitors.)

By:  Mark Cummings

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

By:  Stephen Shaw

     These are called "kickstart capacitors" in switched mode power supply
(SMPS) technology  circuit descriptions. If you ever get an SMPS in with
tripping or low output voltage or amperage, change all small value electrolytic
capacitors (below 330uF and 35v) with high temperature capacitors (105 degree
centigrade).
    

 

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