I have experienced SimasiMac on multiple SE/30 logic boards. SimasiMac in its truest form is a set of HORIZONTAL bars that are very clean with no stray pixels here and there. The Shimada "Repair Macintosh SE/30" web page shows a tiny graphic that somewhat resembles the artifacts shown in SemperFi94's photo, but I've never experienced that myself "as a http://pre-symptom of SimasiMac." But I have experienced that same exact screen garbage (no variation at all from the photos posted by SemperFi94) AFTER recapping an SE/30 logic board. Interestingly, I can only see it at cold boot when I have a IIfx or SE/30 ROM in my motherboard along with 128MB of RAM. For whatever reason, that RAM/ROM combination causes that garbage to appear. Then after the cold boot RAM checks conclude (which take almost 2 minutes for 128MB RAM), the garbage goes away and the machine boots normally.

On a different logic board, which I also cleaned and professionally recapped, I get a different pattern of screen garbage at cold boot (with maxed out RAM and a IIsi ROM installed).

So you may need to recap the board (if it has not been already). And if the caps are good, then perhaps you are merely experiencing what I did due to RAM and/or a non-stock ROM being installed. Even so, if you are not getting sound, then you probably need a board recap. Remove the board, shoot us some crystal clear photos of it, then we can tell you for sure.