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Macintosh IIsi Power Supply Diodes

bibilit

Well-known member
I completely re-capped my first IIsi Sony power supply (it was a mess in there...) a while back with good results except for one odd issue. When first powered on and for ~3-5 minutes after (until everything warms up) if I issue a Shutdown command the IIsi does the shutdown, the power supply clicks but then immediately restarts. As I mentioned, after its been running a while start up and shutdowns work as expected.  

Does this behavior ring any bells for anyone?
Yes, it’s an issue with the main chip on the daughter board being contaminated. 

 

bibilit

Well-known member
This is the chip I am talking about. 

This board was heavily coated with cap goo, making the reflow process hard to manage. 

84FAF0DA-43A6-453D-B110-B6AB81C12059.jpeg

 

Fizzbinn

Well-known member
@bibilit Finished recapping my second IIsi power supply, this one wasn’t as bad cap leakage wise as the first but I did take your advice on the chip on the daughter card. 
 

This picture is after an initial IPA Q-tip cleaning:

87FEF868-1C85-4A6F-80AD-1096E3342CCF.jpeg
 

This is after removing the old caps (which had clearly leaked), cleaning their pads, removing the IC (I used chip quik), and putting some UV mask near the lower cap pads where the copper was exposed:

86D7CBEE-0F87-4C09-9D33-85ED9E3CA10E.jpeg

And the final results after further IPA cleaning, soldering the IC back on, and new tantalum capacitors:

059E4625-A75A-44C9-92E1-3419F62A6A84.jpeg
 

Initial testing after finishing the rest of the recap of the PS looks good, no weird issues with shutdowns!

 

thegarse

Active member
Multiple components fell off my card when cleaning and recapping. Is there a possibility of bypassing this card and have the computer power on without the button?
 

joshc

Well-known member
@thegarse I could be barking up the wrong tree, I'm awake at the wrong hour - BUT... if you twist the power button at the back of the IIsi, it should recess and that will tell the PSU to always be on, bypassing soft power essentially. I don't know however if, without components on that card, that it will work properly still.

However...Why not just put the components that fell off back on? Which ones are you missing? Most of it is diodes and resistors, couple of caps and the main IC... you could just measure components and match them up against the schematics and refer back to a photo to make sure everything is in the right place.

Higher res photo mid way through cleaning/recap, for some reason I never took a photo after it was finished.

1629250606807.png

The top capacitor is a 100uf 6.3V cap. The bottom one next to the M51977FP is a 33uf 25V cap.

There are schematics for the AP41S sub-board / daughter board but I am finding them a bit hard to figure out (again, possibly because I'm awake at the wrong hour). I've attached the PDF that contains them, on pages 12/13.

It is a little tricky as I cannot remember if there's markings on the back of this board or not, but I think with enough effort we could figure out what goes where on this board.
 

Attachments

  • Macintosh IIsi Schematic (bomarc).pdf
    6.5 MB · Views: 24
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