ZX80 Core - new ZX80 motherboards

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
poglad
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Re: ZX80 Core - new ZX80 motherboards

Post by poglad »

Thanks PokeMon, this has arrived - but the old Geburtstag isn't until next week, so I'm not allowed to start building it yet! :D
poglad
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Location: Aberdeen, Scotland

Re: ZX80 Core - new ZX80 motherboards

Post by poglad »

Starting to make some progress! :D
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poglad
Posts: 133
Joined: Mon Mar 24, 2014 3:11 pm
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Re: ZX80 Core - new ZX80 motherboards

Post by poglad »

I've created a Flickr album to show my progress...

https://www.flickr.com/photos/51900952@ ... 628673844/
poglad
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Re: ZX80 Core - new ZX80 motherboards

Post by poglad »

Well I finished building it - looks great, but - ahem - doesn't actually work. The chances of me getting it right first time were very slim, of course! :lol: So I may be asking for some advice here later after I've spent some more time poking around with my multimeter! :geek: Basically, without the NMIX attached the LEDs are solid red from the moment the power is connected, and a vague misty grey pattern appears on the screen. With the NMIX connected, the LEDs rapidly cycle between red and green (depending on the ROM, other positions give red and light blue), and the screen gives a pattern of random black flecks moving rapidly on a white background - like after a ram pack crash.
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PokeMon
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Re: ZX80 Core - new ZX80 motherboards

Post by PokeMon »

There was a missing resistor in the documentation - did you solder R100 ?
And I think I missed it to put into the part set as well (9x10k). :oops:

I updated the documentation file here.
http://goo.gl/RPirnd
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PokeMon
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Re: ZX80 Core - new ZX80 motherboards

Post by PokeMon »

On the picture above seems R100 is soldered. ;)
Did you follow the hints in the chapter about checking soldering points, jumpers and so on ?
Do you have a oscilloscope ?

Please try without NMI board first and ROM switch to 4 (ZX80) and 6 (ZX81).
And don't forget to put two jumpers on J96 when the NMI board is not present.
poglad
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Location: Aberdeen, Scotland

Re: ZX80 Core - new ZX80 motherboards

Post by poglad »

Thanks Karl. I don't have an oscilloscope, but I measured the impedance and voltage etc. at an earlier stage and got the expected figures. I'll work through the troubleshooting chapter this evening and see what I can find. R100 I found, but I also found an additional SMD capacitor that didn't seem to have a home. I'll check again tonight.
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PokeMon
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Re: ZX80 Core - new ZX80 motherboards

Post by PokeMon »

poglad wrote:but I also found an additional SMD capacitor that didn't seem to have a home. I'll check again tonight.
That's okay.
As there is no value printed on, I decided to give one capacitor more than needed to check it's value (the amount of capacitors is different per value which will leave one as a free gift). ;)
Please check all jumpers and the hints in the chapter. Important is R100 and J100 but there are more important things.
Please inspect your board first carefully for any unsoldered or bad soldered pins or eventually shorts.
poglad
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Re: ZX80 Core - new ZX80 motherboards

Post by poglad »

Thanks, it certainly helped with the SMD capacitors! ;)

Measuring the values with a multimeter, the video-related signals are nothing much like the ones in the guide - but I suppose that's because of the random video output I'm getting. I measured CLK on the Z80, and get 2.1V (not 1.8V) and on IC20 I get 1.46V (not 1.0V). Not sure if that's a clue.

Anyway - I had no idea that X1 had any particular orientation - I think I had it back to front. Tried to take it out and turn it round, but unfortunately its legs broke off. :o Well I live next to an electronics store, so hopefully can pick up another but it might not be for a day or two! Perhaps that's all it was! :oops:
poglad
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Location: Aberdeen, Scotland

Re: ZX80 Core - new ZX80 motherboards

Post by poglad »

Those 6.5MHz filters seem hard to come by, so I've just ordered another directly from you PokeMon. Project will be on hiatus until next week! I hope that was what caused the problem - half-expecting you to say "no, doesn't matter which way round you put X1..." :roll:
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