Burnt CPC 6128. Blank screen even with memory replacement.

[Pararegistros]

Hi everybody. First of all, I'd like to make a brief introduction, as I am new to the forum. I'm Jose M. and I'm from Spain.  Thanks to the admins for allowing the registration so quickly.
I am writing as I had a problem with my CPC 6128 with green phosphorus monitor. The point is that some years ago, I bought an adaptor to connect it directly to a CRT TV via SCART connection. It worked fine but one day I was absent minded  and plugged a 12 v power adaptor instead of a 5v one and it burnt.
So I took it to an acquaintance of mine, a guy who saves my ass in many problems with electronics. He replaced the memories with no success and even the z80 processor (I have another one and he even tried to swap components with no success). He has replaced all memories (even some with adaptors), the processor, checked all the circuits with multimeter and osciloscope, and no result. Still the green screen of death.
He told me that he swapped the Z80, the Gate Array and the other chip of which he doesn't remember the name and still didn't work. The only thing he didn't try was the AY chip but, can an audio chip prevent the computer from booting at all?

Could anyone give us any clue of how to repair it? Thank you.

[Bryce]

Hi and welcome,

To answer your questions: Yes, a damaged AY could cause the CPC not to boot. However, if the system got 12V then it's more likely that the ROM's have failed.

Bryce.

[Pararegistros]

@Bryce  Hi Bryce. Thank you for answering. I read in other threads that you recommended a countryman that so I told my technician fellow to try it. He replaced and swapped components (Roms with socket adaptor, Z80...) with the working one without success. The only thing he didn't try was the AY as it is board-soldered.
He's really good but it has been a pain in the ass for some months.

[Bryce]

I thought he replaced the RAMs. I am saying he should replace the ROMs (2x 28pin IC's that are still soldered in your picture above).

Bryce.

[Pararegistros]

Oh, sorry. True. He tried the RAMs not ROMs. He had no programmer.