Strange video output

[Sch-LikA]

Hi !

First thanks a million for the project, I am a retro collector part of a local computer preservation association, I have been looking for an Orao for a while without success ... so I started building an Orao 2007 !

It seems to mostly work ... I see the clock, bus activity, out of reset, some video output but it looks like this :

I tested all chips, tried LS variants, cpu seem fine, rom checks ok ... I don't know what more to test. Do you have any hint ?

Thanks for helping !

[mejs]

hi @Sch-LikA

Do you have pin 27 on the EPROM tied to either ground or 5V? It's used to change selection between the two ROM versions (102 vs 103).

You can either do it directly, or install an spdt switch or headers in the 3 vias to the left of the EPROM:

[Sch-LikA]

Hi,

Thanks for the fast answer. Yes I have a jumper installed, I tried both positions. I used the orao2007.jed file from the original orao2007.zip file for the gal, I guess it is the correct one ?

[Sch-LikA]

I came across this old Twitter post you did :

https://twitter.vladovince.com/mejs/status/1338576472378839043/

It somehow looks similar to my issue (before the eprom stuff), have you replaced some capacitors/resistors to get correct video output ?

[mejs]

Hi @Sch-LikA , you can see that whole thread archived here: https://twitter.vladovince.com/mejs/status/1336461869662474240/

To resolve this particular issue, I had to set the rom selection jumper. It sounds like you've already done that.

In terms of the GAL chip, I used that exact jed file.

I'll let you know if I think of anything else, unfortunately I don't have another idea immediately. I would start with simple troubleshooting like checking data and address lines and nothing anything out of the ordinary.