I recent;y acquired a faulty imac orinal type.
On startup it chimes immediatly and then switches
off, so it can't be going through the startup process.
Can anybody give me a list of things to check?
The CPU must be working or it would't startup at all.
The AC adaptir? the memory at fault causes PC's to
stick with a continues beep.
Any suggestions would be appreciated.

if it is an original imac, the symptom will be the power light turns green and then yellow, 99% will be the bad flyback transformer. you can hook up a MAC muLtisync monitor to the video out put jack (db-15 wide type) you should see the desk top OK if the transformer is bad.

This imac has information about this imac attached
on the inside. So I removerd the ligic board and
tookk the grill to reveal the SODIMM memory.
Following apple site instructions I removed the
SODIMM memory and then reinstalled it. Then the
imac stayed on after the chime and I heard it
acessing the HD so something must have been going
but the screen was blank. So I took the logic card out
again and there is a Video connector on part of the
motherboard and by it a SODIMM like medium lenght
card. I Pulled that out and reinstalled it to see if that
might affect the graphics monitor.
I will try it soon. Can anybody advise me what next
steps to take please.

Budm gave you the best advice, it is most likely the video board. The whole thing is a pain to take off. Had to replace one yesterday. Just be careful when you get the part. If you can't do it yourself let a pro do it for you since it is a little bit delicate. You can try replace the cmos battery but I don't think it will help.

As the light stays red so I accept the video card
possibity. I have removed and re-installed the card,
as I found out how to do that. All I need to do knoow
is check both IDE cables as know it doesn't turn off
immediatly after the chime.
I will post what happens when I do that.
I suspect I'll need more advise and help for this
project.