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Elfen

LC III Circuit Mysteries

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Was looking over the dead LC III 25MHz, and saw an empty capacitor spot (C17). So I thought, "did I forget to put a cap there during recap?" I checked it with the other LC III (a 33MHz) that works. C17 spot is also missing on the other board.

 

Then I looked over the two boards, and I found a lot of dead end areas. This one on the top of the board in particular as a 10µf capacitor was recapped in this area. Which I have a question...

Part%20of%20LC3.png

 

I can not see where the trace goes because "U32" is covering it. But from that I can make out, it loops back to C18. And the middle trace goes to an empty pad area.

 

Does that loop trace goes under the VRAM Chip at location U32? I have a feeling that it does not.

 

And there are other funny areas I found looking for dead traces. Underside of board R71 is one such area that goes to nowhere as there is no R71. Again on the underside R88 is another, a trace comes out of it to a junction to the other side BUT there is another trace that breaks at that point because R88's trace is in the way. I found several funny spots like that, confirming them with the working LC III.

 

So... why so many funny areas? This makes looking for broken traces when one runs into a dead end spot. An in the case of C18, it is necessary or can it be removed? That depends if the trace goes under U32, which I can not see.

Edited by Elfen

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does your board look like the one in this thread?? Maybe it had the "official Apple mod" because it had a PCB problem.  Then someone got it and thought it was a crazy mod so took it all off?  Just a thought :D

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It's funny, MiniMOJOMan - both machines have this and other strange circuits on the mother board.

 

At first I thought it was trace rot, but most of these are on the underside of the board where trace rot does rot happen. Then I ket looking and saw that some of these go nowhere like an empty ic pad area or stops in the middle of nowhere. Its time to get batteries for the digi-cam. This is really weird.

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