well, as you may have read I foolishly fried my falcon by plugging the floppy connector to the ct63 wrongly some time ago. Now that I am in pre vacations mode I had a chance to revisit it. First of all i found my original 4mb card and connected it.
Then I connected the falcon to a vga monitor that said the signal out of range. So joyfully I thought to check on a tv. So I get this pattern on the screen:
The only physical damage I see (on the top of the board) is this:
I wonder if it will be repairable.
5 years age did something similar. I'd misaligned the ST RAM card while installing the CT63. Unfortunately had a PC supply connected that didn't trip due to it's high rating. Took both the MB and card out.
I had the VIDEL, COMBEL and CPU replaced without success.
This one started cooking just to the left of the Falcon power connector before catching the mistake. The ST RAM card was fine. Without a scope, all I really could do was ring out traces, and as it's multilayer, proves difficult.
The diagnostic cart doesn't really help in these situations.
From what I've seen here is first thing the experienced users do is see if the CPU starts, and gather that indicates it's reading ROM.
Traced most every 5/12v lines, power off for continuity, didn't think at the time to check resistance of said to ground. I guess that's one way to check for a short, which I'm sure you know Chris. From hacking on Falcons over 20 years, the damn things will boot with a lot of things bad. One of Rodolphe's quotes to me once was "caps" don't care, so took that in mind to check lastly.
I've over the years accidentally connected the floppy cable inverted, not long, but have never damaged a board doing so (since started using a permanent marker on the top of ribbon cables!) If an IKB or something was bad, the cart would catch that. If the cart doesn't work, board isn't even getting past that check to boot from cartridge port. Kind of narrows it down a bit, but know this is pretty basic stuff here. Reading through the sequence of TOS initialization can get a basic road map to follow.
Know you have the tools. dml has said he's been repairing Falcons on the side for some while too, as well as the offer in this thread (sorry can't see usr name in the editor).
One thing I've forgotten to mention, on two occasions with dead Falcons, turned out to be one of the BUS GAL popped for some reason. There's are a simple fix. Might try burning a set to try. Forgot now which U number it was, both times it was the same GAL I do remember.