Already dead A1200
 

Rather than killing my own machine, I decided to do something different and bought an already dead a1200 :D My intention is to fix my other 1200 that doesn't accept hard drives, using the parts of this new one.

But I this one is showing signs of life. When turned on, power led works, it checks the hard drive for a moment but doesn't display any image and remains silent. After stripping the motherboard off, I noticed that it was very dusty and edges of the board are a bit worn but there is no visible damage on the buses. What might be the problem of this one?

Since it checks the hd it seems it is working but has problems accessing the hd. If there was a serious hardware problem it wouldn't get that far !
I would suggest first disconnect every additional hardware like harddisk or turbocard etc. Then check the Amiga with all 3 different signal outputs. ( RGB, Video, RF ) Also try holding down both mousbuttons on startup. This should bring up the startmenu.

I removed everything and am trying to get the bare board working. Monitor or TV doesn't display anything but I can see the usual "power on flicker" when it is turned on. Start menu doesn't appear and reboot keys don't do anything although caps lock light turns on/off fine.

Do you mean, when you power on, the power LED goes on as normal and then becomes brighter as well as the caps lock LED goes on and off. And when you press caps lock, the caps led goes on and off as you press it. But when you press Ctrl-Amiga-Amiga, nothing happens, even the caps lock LED continues to work normal ? This sounds really strange. As if the AmigaOS is answering to key strokes (otherwise caps lock would stop reacting after 10 presses) but the reset line is not connected (because otherwise the power-up procedure would repeat from the start after Ctrl-A-A). Ctrl-A-A causes a hardware reset, just the same as power-on, so this should *always* react. Perhaps one of the damages is the keyboard cable.

I'm sorry Ctrl+A+A blinks the caps lock once and this must mean a successful reset but I'd expect the power led to dim for a moment when restarting. This doesn't happen. Still, I can confirm the machine resets with keys.

Keyboard problems aren't the issue however. As I said, the bare board has the problem with nothing connected.

Floppy drive doesn't show any sign of life unless I accidentally connect it's cable the wrong way :p

Probably a CIA damage.
These SMD A-1200s boards are harder to repair than the old A-500 which had every chip socketed ;)
I even have one A-1200 board that works but doesn't display any screen ( drive, sound and everything else works ok, though )

Thanks for the tip, I think it's still good enough to fix my other board with.