Check also C1, C7, C12, C13 which are also +5V bypasses to ground that you probably recapped (47uf/16V). There are also a ton of .1 and .01 SMT caps on the underside that bypass +5v, however these rarely short unless mechanically disrupted.

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Wally you'r so precise ! This evening i tested all capacitors you suggested: it seems that C13 had been ground shorted. There was a lifted and broken plate so when i tried to connect C13 to the remaining "underlevel" ground point i guess i've intercepted a +5 line on the upper surface. I rerouted C13 ground lead to C11, the nearest ground point known and i obtained 233 ohm reading between J12-12,13 and ground. No more ground short.I still have some concerns about the continuity of this 5V line, we'll see.

http://img61.imageshack.us/img61/4899/627lh1.jpg

Then i tested some lines i thought fine

UB10-15/UB11-15 +C5- ground line is fineUB11-10 +C4- ground line is fine

UB11-7 +C6- ground line is fine

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In particular UB10-15/UB11-15 +C5 line, whose reading wasn't properly 0 ohm but something between 1 and 2 ohm. The trace was lifted (not broken) but i guess neither this nor cold joint was the problem. May be it was corroded somewhere increasing resistance value: this leaded me to rework these audio circuits with some bypasses.

http://img89.imageshack.us/my.php?image=633zd6.jpg

Now overall +5 line to ground resistance has misteriously increased to 290 ohm.

http://img207.imageshack.us/img207/2342/637nr5.jpg

Tomorrow or the day after tomorrow when i have some time i'll try if it starts (i've Se30 remaining parts in my old house) and i'll let you know.

I'm really excited cause i'm waiting my fourth apple IIgs (SCSI card equipped) deliver from germany. Vintage apple computing is taking a lot of time in my life, i would avoid not to become haunted. [] ]'>