I have just tested voltage of the 5.00v line on the analog board connector and the reading was 0.30v. It sometimes fluctuated but stayed steady on 0.30v.

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I would highly recommend getting a copy of Macintosh Repair & Upgrade Secrets by Larry Pina if you can, there is a lot of discussion on testing voltages on the 128/512 and failed component identification.

Used copies seem pretty inexpensive at the moment: http://www.amazon.com/gp/product/0672484528/ref=oh_details_o06_s00_i00?ie=UTF8&psc=1