OSI 600D Superboard Build

[rubber_jonnie]

I think the fuzzy video thing is due to the change in speed (and manufacturing process) between now and the 1970s.

I wouldn't be surprised if it's that at all.

Indeed, I'm surprised that the BoM didn't state a specific manufacturer's part as the timings differed so greatly back in the day. There are many systems where the service manual states manufacturer and even down to build date for replacement parts.

It think this was in part due to Ohio Scientific providing all the parts in the kit, so you didn't buy a bare board back in the day and supply all your own components. I haven't seen any indications that it came as a bare board at this point, but I could be wrong.

The BoM does state alternatives, but in the case of U21, it's another LS04. I've also ordered some 7404's to see how they fare just out of curiosity.

I've just set up the jumpers for cassette operation, so need to see if that's working now. More fun and games, then I can build the 610 expansion board :)

[rubber_jonnie]

OK, so I tried this which I had kicking round in a drawer.

It's just a composite mod I made for an Atari 2600 (I think) that I abandoned and bought a ready made one for that included a nice cable and audio built in too.

IMG20240329145534.jpg

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And there is a definite improvement with the LCD.

This is before:

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This is after:

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However this is the CRT with it:

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And this is the CRT without:

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Personally I prefer the CRT without.

I think there is scope for both a CRT out and a VGA out, since with the mod I can get the pot at R58 adjusted well to work on both outputs.

[rubber_jonnie]

I've been looking at cassette saving for the OSI today for fun ( :excited: ) and have hit another issue, possibly another dead IC, and though the TL866 says otherwise, I have ordered a replacement just in case. I also managed to find some 7476's as well so those are also on the way.

It would be nice if I actually had the IC's I need in stock, but like with capacitors, it's just never the case :pullhair:

When I run the 'SAVE' command (It's a weird and wonderful way to save, but that's another story) I can see the data leaving the 6850 and getting to where it should do in the last IC in line, U64, a 74LS76.

However, it should then output from pin 15 to the other gates, but I just see a constant square wave...

I don't have any shorts, but what's coming out of pin 15 should represent what is going into pins 2,4 & 16, and it just isn't. I did also remove the IC but there was nothing on pin 15 coming externally, so it has to be coming from the IC. So I lifted pin 15 and it's definitely being generated in the LS76.

The BoM says SNC5476J, 7476 and 74LS76, so it's looking like another possible timing issue due to a modern chip.

I probably won't use cassette much, but I want as much working before I start off on the 610 expansion board.

[rubber_jonnie]

I also managed to find some 7476's as well so those are also on the way.

Annoyingly the supplier of the 7476's had a stock error and canceled my order. They issued the refund PDQ, but I'd rather have had the IC's. :pullhair:

EDIT - Just found some at Cricklewood Electronics, I certainly recommend them as a supplier.

[HigashiJun]

Annoyingly the supplier of the 7476's had a stock error and canceled my order. They issued the refund PDQ, but I'd rather have had the IC's. :pullhair:

EDIT - Just found some at Cricklewood Electronics, I certainly recommend them as a supplier.

:dizzy:

[stephen_usher]

EDIT - Just found some at Cricklewood Electronics, I certainly recommend them as a supplier.

Yeah. They're reliable for old parts, though not cheap.

[rubber_jonnie]

Annoyingly the supplier of the 7476's had a stock error and canceled my order. They issued the refund PDQ, but I'd rather have had the IC's. :pullhair:

EDIT - Just found some at Cricklewood Electronics, I certainly recommend them as a supplier.

:dizzy:

Exactly...

[rubber_jonnie]

EDIT - Just found some at Cricklewood Electronics, I certainly recommend them as a supplier.

Yeah. They're reliable for old parts, though not cheap.

Yes, definitely not cheap at all, but at the moment I'll take reliable over cheap!

[HigashiJun]

Yes, definitely not cheap at all, but at the moment I'll take reliable over cheap!

A wise man decision...

8-)

[chronicthehedgehog]

I've got 40 SN74LS76AN on my shelf if you need more. I bought a good job lot a couple of years ago. I got a bit OCD about 74X at the time :D