Many thanks to all for the answers, your help is very much appreciated.
The computer is not in my house, it is a young musician who has decided to start in the Atari world to control their electronic instruments and compose their music; but it has started with a bit of bad luck.
- Atari 1040 STfm (without mods).
- Video cable for high resolution, manufactured by "Retrocables" (http://retrocables.es/tienda/index.php? ... &id_lang=1
- The computer with that cable was working correctly, but after moving the computer: says the boy who does not turn on the monitor now.
- I told him to try an RF cable to verify that it was not a problem with RAM or power supply: it actually works correctly with the RF cable.
- Unfortunately he does not have an oscilloscope, but all your indications will be what he will write down and deliver to an electronics technician in his city.
I do not know if this fault is typified or is common in the ST, I have searched and can not find much information, but I believe that with all your advice given to the electronics technician he will be able to resuscitate the computer.
Checking the video adapter cable is also a good idea, because previously it worked but I have met people who have even connected the DIN upside down ...
Thank you very much, guys, I take note and send to him all the information we collect.
ST/fm/e, STacy, Mega ST/e, TT, Falcon, C-Lab MKX... and more music tools.