Yet another SubElectro MC type Fantazia/Pisces ???

[NivagSwerdna]

Pin 24 of the Z80 (labelled /WREQ on the galaxian schematics) is actually the /WAIT line and is driven by a 7474 at 6S to only allow writes in the blanking period. check that is toggling correctly.

I like your thinking. I have actually replaced 6S before during this saga and it seems to be toggling but I think it must be something like that.

 

[NivagSwerdna]

Hm...

Socketed and replaced 6C because I thought I saw glitches on 1H, n1H... but that was probably an artefact of my cheapo USB logic analyser because that made no differece.

Socketed and replaced 3R because that is part of the nWREQ logic (and 6S was replaced earlier)... no change.

Maybe the 74LS157s next... but which one?

NivagSwerdna2022-09-26 19:54:16

 

[NivagSwerdna]

So I get back from holiday and cannot remember exactly what I did last! Looking at the board it looks like I decided to change the 74LS157 at 3L (which is the same as one suggested by Macro a while back)... and...

and

and

... quite pretty really.

We are done! Quite a relief. I can pack that away and work on some non-arcade related projects for a change.

NivagSwerdna2022-10-28 19:53:19