Amiga 3000 video problems (ie: NONE) (UPDATE: Success)

[Castellen]

Yep, I'd agree with Olecranon, check again that J350 is in position 2-3 (A500 position).  If you have an oscilloscope handy, check on that jumper, or on U350 pin 19 that there is a square wave present.
I forget what the frequency is, I don't have my notes handy, but can look it up if you want.

An interesting thing with the A3000 is that it has a seperate +5V power supply for the video section, referred to as +VID.
It's supplied on pin 1 of the power connector (look for the square pad on the solder side of the board) and check you have got 5V on U450 (Denise) pin 19, this is the +VID supply.

You can join pins 1 and 2 of the power input socket together which just makes +VID the same as +5V.

[Castellen]

2V on the +VID supply is a bad thing, that's probably why it's not working.

Check on pin 1 of the motherboard power connector (it's the one that has a square shaped pad on the bottom side of the board).

If you have 5V on there, there is a supply interruption somewhere.  I don't think there's any fuses on the +VID line, I'll look over the schematics later if you can't work it out.

If you don't have 5V on pin 1 of the power connector, just join it to pin 2 (link power supply socket pins 1 & 2 together) then you should be in buisness.  Pin 2 is the main 5V logic supply, which is obviously working, else the computer wouldn't run at all.

Forget about checking the state of the TICK line at the moment, get the +VID supply working first, which will probably solve all the problems anyway.