If I recall correctly from my experiments, the IIx ROM does exactly that in a IIci - gray screen - so I would rule out using the IIx ROM right away. It might work in your IIcx but I wouldn't count on it in the IIci. The machines are very similar but they are in fact different in some ways when you start swapping things between them.
Did you try connecting the display to the onboard video and without the IIx ROM SIMM installed? That's an important test.
When you say that the hard drive "spins up and starts working", does this mean that it started making sounds like it was loading something off of the drive? If so, that would mean the IIci has trouble with loading the OS. It is completely possible that the exact same hard drive will death chime on a IIci and not on a IIcx -- for example, system 6.0.3 works fine on IIcx and not at all on IIci. If this is happening, it is conceivably a separate issue from the black screen.
The test for OS-related death chime is to disconnect the HD and see if it still death chimes.
Also, does it make the normal startup chime at first?
The fact that your IIci makes sound and responds to the power button properly is evidence that your caps are still pretty good.
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As for the Mac II/IIx, if this was the source of your ROM SIMM, did you remember to put it back in there before turning it on? I think it'll do something like you described without that in there.
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trag: I had a IIci logic board that was badly scratched through a number of traces, and one additional trace underneath the battery holder was corroded open from a very slight battery leak. Also very bad, messy caps on that Mac.
Did you try connecting the display to the onboard video and without the IIx ROM SIMM installed? That's an important test.
When you say that the hard drive "spins up and starts working", does this mean that it started making sounds like it was loading something off of the drive? If so, that would mean the IIci has trouble with loading the OS. It is completely possible that the exact same hard drive will death chime on a IIci and not on a IIcx -- for example, system 6.0.3 works fine on IIcx and not at all on IIci. If this is happening, it is conceivably a separate issue from the black screen.
The test for OS-related death chime is to disconnect the HD and see if it still death chimes.
Also, does it make the normal startup chime at first?
The fact that your IIci makes sound and responds to the power button properly is evidence that your caps are still pretty good.
----------
As for the Mac II/IIx, if this was the source of your ROM SIMM, did you remember to put it back in there before turning it on? I think it'll do something like you described without that in there.
-----------
trag: I had a IIci logic board that was badly scratched through a number of traces, and one additional trace underneath the battery holder was corroded open from a very slight battery leak. Also very bad, messy caps on that Mac.