Uk Sony HB 75 corrupted and artifacting screen, vram already changed

By Cypher007

Supporter (3)

Cypher007's picture

23-10-2019, 23:52

Trying to fix an HB75, I’ve replaced the vram with new old stock 4116’s and the display is exactly the same as before. Here is also fast moving groups of pixels that flicker in some areas of the screen.

I will try and attach some pics and vid of before and after I changed the vram.

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By Cypher007

Supporter (3)

Cypher007's picture

23-10-2019, 23:52

By Cypher007

Supporter (3)

Cypher007's picture

23-10-2019, 23:52

By Wild_Penguin

Hero (546)

Wild_Penguin's picture

24-10-2019, 19:38

Hi,

That doesn't seem like the simple VRAM errors I've seen elsewhere (where one or several bit is wrong or stuck). More like addressing error or some signal bleeding (mirroring / bouncing???). Looks very weird, since characters are repeated (but correct characters!). Check the VRAM traces - are there shorts? Maybe VDP is broken?

But I'd also wait a little for more replies, since probably some HW guru will answer here (I'm not one...).

By Grauw

Ascended (8456)

Grauw's picture

24-10-2019, 20:23

I agree, there seem to be issues with the AD1 address pin. But very strange indeed that character patterns are read correctly, one would expect those to have mirroring issues as well.