exxos's Atari, Amiga & retro forum

Orientation is now correct, thank you.
I am now getting a black screen with white border. Research indicates this means no ram. Makes sense now that the original chips are gone, but it is clearly not picking up the new boards either.
I reseated the new components and verified no little legs were sticking out of anything they shouldn't be.
I found a bodge wire underneath the board that had unmoored itself on one end, so soldered that back onto the spot that appeared to be the most likely, given the shape and length of the wire, but this made no difference.

I also unsoldered the "switch" on the mmu board to being it to 1MB instead of 4MB, in case there was some compatibility thing with this revision board.

I don't see anything obviously wrong. After reseating the mmu a fourth time, I now have vertical bars on the black screen with white border, if that matters.

If this turns out to be toast, I may end up turning this into a Rastari machine with original case and keyboard, etc., and I still have another 520STFM in mint condition that is identical to the one from my childhood, which will be staying as is.

I think you have the RAM cable in upside down going by the image you posted a few posts back.

I swear I read somewhere that said make sure the blue tabs are pointing upwards, but no idea where.
Regardless, I just swapped it around and made no difference.

I will also say, the one ram chip on the mmu board is getting hot. Just the one, presumably because the 4MB switch is desoldered now.

If you powered on with the MMU adapter in the wrong way round you may have killed it.

TBH it sounds like you may not be plugged in far enough.

So on the fourth reseat I tried to really press it in there, and that is why I now have vertical lines on the black screen with white border. It's as far in as it will go, short of maybe standing on the thing.

Gentlemen, thank you all for the assist. I assume it is toast and will either leave this alone for now, or I'll see about getting a replacement from the store.