Introduce myself first.

I'm a retro computing enthusiast and recently got an Enterprise 64 because I just love the machine.

Also tell you that I write in English because the Hungarian language (sorry) I do not know.

I tell you: after buying an Enterprise from Ebay from the famous Egyptian seller, he is not responsible for the repair aid, of course.
But I have met you and read repairs from people who seem very knowledgeable here.
I have not opened it yet but I have been able to check the power supply (it works correctly, 12V) but the screen shows me this image.
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I think it is the screen before starting the computer startup test. I've seen a video on youtube where it seemed to show this before the colorful "ENTERPRISE" message.
Could someone tell me where to start diagnosing?

Thank you all in advance for your help and for accepting me in this forum.

Javier

Welcome here!

This is screen: uninitialised Nick chip display power on garbage of video RAM.
It is means the system freeze before the ROM enter to the display initialisation phase.

Most possible problems:
-dead RAM chip. The original EXOS ROM have a bug: put the stack pointer to untested RAM, and if onboard memory faulty can't report the fault because using CALLs, which are never return.
For this situation I wrote small test, what I also recommended to others.
-faulty Z80. Already found some, all are Zilog type, made in Phillipines serie. Some are really crazy: can execute program, but when write to RAM one or more bits are faulty.
-defective Dave chip. One or more outputs are dead. If the /ROM signal dead can be replaced with few 74 series chip.

Welcome here!

This is screen: uninitialised Nick chip display power on garbage of video RAM.
It is means the system freeze before the ROM enter to the display initialisation phase.

Most possible problems:
-dead RAM chip. The original EXOS ROM have a bug: put the stack pointer to untested RAM, and if onboard memory faulty can't report the fault because using CALLs, which are never return.
For this situation I wrote small test, what I also recommended to others.
-faulty Z80. Already found some, all are Zilog type, made in Phillipines serie. Some are really crazy: can execute program, but when write to RAM one or more bits are faulty.
-defective Dave chip. One or more outputs are dead. If the /ROM signal dead can be replaced with few 74 series chip.

Thank you Zozo!

Yeah, I also thought that the initialization process failed to start because I have seen those vertical stripes momentarily in a Youtube video.

As I said, I'll go for the RAM check first and then move on to other possible factors.
This kind of error has happened to me with countless ZX Spectrum, with an Apple II, with a QL... I think your first diagnosis is correct enought.

I hope that with a simple caress on the chip you can find the possible guilty memory!

Finally to say that I was pleasantly surprised to find such nice guys here.

Thank you!

Javier

Where in Spain do you live, Javier?