Dick Smith Super 80 computer kit

[Peter]

The recommended cassette player was one of those flat portable ones from yesteryear. You could have batteries or run it off a power cord.

I know the ones, probably garage sale jobs these days. Do you think the VZ300 job will work then?

Got your email, thanks!

No worries. Most Street Directories cover Blue Mountains, I'll email you some directions.

 

Do you have a working composite b/w monitor with a RCA socket as input? If so I could bring one of my super-80's over for you to look at.

I'd love to see a working one. I've got a Micobee amber screen (I think) sitting next to me, could be green. will that do? It's got RCA input.

[Robert]

Hopefully your monitor and cassette recorder will work, won't know until we try it I guess. But need to get yours to boot up first of course! Any progress?

[Peter]

Hopefully your monitor and cassette recorder will work, won't know until we try it I guess. But need to get yours to boot up first of course! Any progress?

The Microbee monitor works, strangest thing is though the picture artefacts are very similar to the VHF modulator output (sans noise) there's no door step and the character grid is a little snakey. I think there's some interference somewhere in the video generation ciruit. There's also some sort of scrolling from bottom to top.

 

At this stage I'm confident that the video circuitry can be debugged and tuned. I can't get the test mode to work at all so I suspect that the CPU circuit isn't quite right. I'll concentrate on that in the short term.

 

This is my plan of attack.

 

1. Verify ROM images

2. Verify CPU is functional

3. Check address and databus integrity (using DMM)

4. Check memory decode logic

 

What I would expect to find is that some logic chips may be defective and or the pins aren't making good contact in the sockets as you suggested earlier. I'm wondering if I should pull all the chips out again and start assembling from scratch following the guide. Before that I'll do steps above.

[Robert]

And, you might be able to compare some waveforms to my computer.

[James]

Let me know how things turn out

[Peter]

At least I have a few spare TTL chips. One thing that I haven't asked you is if the PC board (out of the box)needed any mods before it worked apart from the link for BASIC in ROM and the suggested improvements.

 

And, you might be able to compare some waveforms to my computer.

 

That's a good idea. Especially the video circuit, something's not right there.

[Robert]

Yes, that part of the computer has far more chips than it should have had.

 

btw, does Garos have a Super 80 as well? He seems to have disappeared...

[Peter]

Yes, that part of the computer has far more chips than it should have had.

 

I agree, it seems the most complicated part of the system. I've pulled all the chips and started rebuilding. I've found an initial problem with the signals. The output of U30/pin 11 is supposed to be 15 kHz odd, but mine is 32kHz, I've swapped the two chips involved and still get the same value. I'm wondering if the manual is wrong. U30 is a 74LS86 (XOR) (combining 15K and 32K sigs) and U36 is a 74LS92 (div by 12) Can you check yours for me? Up until this point all signals are correct, I'll have a closer look tonight but it's quite suss.

btw, does Garos have a Super 80 as well? He seems to have disappeared...

He had one and he's keen on getting another.

[Robert]

Unfortunately all my test gear is over at my other house, as is my TTL manual.

 

However, on my circuit diagram I have marked all the theoretical frequencies, so let's see how we go. All frequencies are HZ.

 

U30 pin 11 and 13 = 15625; pin 12 = 31250.

U36 pin1 = 93750 ; pin 9 and 11 = 31250 ; pin 8 and 14 = 15625 ; pin 12 = 7812.5

 

Some more if it helps:

U31 pin 1 = 7812.5 ; pin 9 = 3125, pin 8 and 9 = 1562.5, pin 12 = 781.25

U28 pin 1 and 3 = 15625, pin 2 = 31250

U39 pins 1 and 2 = 15625

U38 pin 12 = 375000, pin14 = 197500, pin10 = 93750, pin2 = 46875, pin4 = 15625, pin6 = 781.25

U43 pin 10 = 390.625, pin12 = 195.3125, pin14 = 48.828125

 

Hopefully there's not too much crap in that lot!

[Garos]

Yes, that part of the computer has far more chips than it should have had.

 

btw, does Garos have a Super 80 as well? He seems to have disappeared...

 

Hi Guys,

I made a reply but it vanished... oh well

 

as I mentioned afore, I built an S80 in 1983 which I unfortunately ditched in when it became disfunctional

for it I built two graphics cards, the second being the 80x24 b&w card

 

I have been trying to decide whether or not to try to reproduce a super 80 (tis about $150 to have a 30x30cm double sided board made) or to design and build my own machine based on pre 1980's technology.

I have been looking into the latter and am becoming more and more interested. The 68000 came out in 1979 and sounds like an excellent chip to become familiar with, though being 32/16 bit increases the complexity of the circuit. Anyhow, will keep you posted.

 

I am away on Sun 19th, but hope you guys have an enjoyable and successful time.

[Robert]

I intend to do just that. It's a pity you threw out the broken Super 80, oh well. Good luck with your new project.

 

My super 80 has an interesting mod... instead of 4116's it has 4164 (64k x 1) RAMs. It meant I could get rid of the -5volt supply and only have 8 ram chips, and I get 52k of RAM.