exxos's Atari, Amiga & retro forum

rubber_jonnie wrote: 26 Jan 2024 10:52 I think the PISO is U42, an LS165. I'll give it a check later. I really should do some work now though!

Yeah, same here. :-)

So this is new:


Looks like there is some problem with mixing the video. It comes and goes.

@rubber_jonnie

Your retro OSI seems to like Modern Art...

:lol:

HigashiJun wrote: 26 Jan 2024 11:43 @rubber_jonnie

Your retro OSI seems to like Modern Art...

:lol:

It certainly does!

You've added a colour mod, obviously. ;-)

stephen_usher wrote: 26 Jan 2024 11:56 You've added a colour mod, obviously. ;-)

I'd like to say yes, but no...

:dizzy:

Now if only you could replicate that cool effect once its running :D

PhilC wrote: 26 Jan 2024 12:38 Now if only you could replicate that cool effect once its running :D

That is running!

well, ish...

For certain values of "running".

OK so the current state is that I have removed all the ROMs bar the character generator. In this state I should get a screen filled with one character, OSI character #255, or if not that, random characters.

The output of U70 pin 11 goes to pins 9 & 10, and this also provides composite sync on pin 12 of the rear connector on the PCB.

The video signal, as best I can tell, comes via pin 2 of the gate formed by pins 1,2 & 3 on U70 and are mixed by the gate formed of pins 4,5 & 6.

Here we can see the circuit where I believe it is all mixed:



And the trace from pins 11 and 6:


The 'scope shows pin 11 of U70 (Effectively composite sync) on the yellow trace, with the pin 6 (Video signal) on the blue trace. It seems like both parts are there ready to be mixed.

I would expect to see the sync and video signals mixed at pin 12 of the rear connector, but I only see composite sync at 15.63Khz.

That suggests that the signals are not being mixed at all. Wondering if R58 is duff, as that seems to be where the mixing is happening.