CPC464 Video Issues

[wyldcat34]

Hi guys,
Hope all is well.  Can anyone tell me what this issue may be?  If I run a tape game it loads properly, but it just looks like static.  If I turn it on and type a word and hit enter enough, words do appear but mirrored - see the pic attached.


Any ideas? As my electronics skills is pretty much nothing!   Cheers all!

[Bryce]

Possibly a RAM problem or an address line between the CRTC and the RAM? It'll be an interesting one to debug.

Bryce.

[wyldcat34]

Yeh, my debug skill is to turn it off and back on again

[AMSDOS]

My Hardware skills are virtually zilch when an Amstrad is concerned, if it was a PC I'd tell you to replace the video card or monitor 


I was trying to think back to when we had a Green Screen 464 and was wondering if it had some knobs at the back of the monitor with one that played around with the Vertical Hold? The screenshot you sent made me think that it was that which was out of alignment, though usually the screen moves around.

[gerald]

As Bryce said, it looks like a bit stuck on one address line from CRTC as it duplicates the screen. My bet is on MA5 as it repeate every after 10liner - 8 char = 64bytes of linear address.
However, this cannot explain the "load" corruption nor the dots.
The problem could be either on CRTC or the (CPU/CRTC/RAS/CAS address mux), but likely on CRTC side otherwise the Z80 would fetch corrupted data from RAM.

Can you post a picture of the screen at boot with a border 26 command (so we clearly see the border)

[TFM]

Also the CRTC get's initialized wrong: So maybe a ROM problem or a CRTC problem.

[Gryzor]

As Bryce said, it looks like a bit stuck on one address line from CRTC

Maybe try blowing on it or nudging it gently?