GS Rom 0 Stuck on Firmware Splash; blown disk controller.

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GS Rom 0 Stuck on Firmware Splash; blown disk controller.

One of my other GS logic boards has a logic fault: When powered on, it hits the Apple Firmware splash screen, but it never attempts to scan for drives or devices. With no drives connected, it does not reach the 'bonk', 'No devices' screen, and I cannot exit to the Control Panel. It is stuck solid on the splash screen. 

 

This unit has always been a drive tested for rebuilding and aligning drive mechs. I'm pretty sure that someone connected a Mac drive to its Disk port, which likely fried something. 

 

What components should I be examining on the mainboard itself that could have fried, that would cause this?

The 'SLOTMAKER' ? Anything else?

 

(I need to look for my old blue Apple Service binders and see if I have the GS diagnostics chart, but those books rarely covered component-level repairs.)

 

I have other GS boards, but this one is by far the cleanest of the lot.