ZX80 no "K" prompt
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ZX80 no "K" prompt
I was hoping someone could assist me.
I built a ZX80 kit which follows the original 1980 track layout. The machine produces a raster complete with little distortions every few pixels and a little kink at the bottom. Exactly as my other working board does, except the "K" prompt is missing.
I have tested the board with a known good processor and ROM (2532 with Vpp tied to Vcc). I even made a 27C32 to ZX80 Mask ROM adapter which requires the swapping of the two lines, A11 and E etc.
I'm also using the exact same clock crystal configuration as my other board.
Could you please give me an idea of where to look next?
I built a ZX80 kit which follows the original 1980 track layout. The machine produces a raster complete with little distortions every few pixels and a little kink at the bottom. Exactly as my other working board does, except the "K" prompt is missing.
I have tested the board with a known good processor and ROM (2532 with Vpp tied to Vcc). I even made a 27C32 to ZX80 Mask ROM adapter which requires the swapping of the two lines, A11 and E etc.
I'm also using the exact same clock crystal configuration as my other board.
Could you please give me an idea of where to look next?
ZX80/ZX81/ZX Spectrum
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Re: ZX80 no "K" prompt
Could please you post a photo of the screen display that you are getting.
Mark
Mark
ZX81 Variations
ZX81 Chip Pin-outs
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There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
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- Posts: 77
- Joined: Sat Aug 18, 2012 12:44 am
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Re: ZX80 no "K" prompt
I'll upload a picture, but there's not much to see. It looks EXACTLY like it does when the K is present (along with all the normal background image artefacts), there's just no "K".
ZX80/ZX81/ZX Spectrum
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Re: ZX80 no "K" prompt
http://www.myprius.co.za/zx80error.zip
Sorry for the ZIP file, but I wanted to get as high rez as possible. Two photos of the early build snuck in.
Thank you for trying to help.
Sorry for the ZIP file, but I wanted to get as high rez as possible. Two photos of the early build snuck in.
Thank you for trying to help.
ZX80/ZX81/ZX Spectrum
Re: ZX80 no "K" prompt
I would say CPU or RAM. Do You have another Z80 to swap?
Mathias
ZX-Team member and classic computer collector
ZX-Team member and classic computer collector
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Re: ZX80 no "K" prompt
I plugged in a known working RAM pack (which disables onboard RAM) and also swapped in a known working CPU to no avail.
ZX80/ZX81/ZX Spectrum
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Re: ZX80 no "K" prompt
What is the Z80 doing?
If you have suitable test equipment, test the clock input on pin 6, and the various control output signals. Also the data bus and at least address pins A0, A1, A14 and A15.
Mark
If you have suitable test equipment, test the clock input on pin 6, and the various control output signals. Also the data bus and at least address pins A0, A1, A14 and A15.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
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- Posts: 77
- Joined: Sat Aug 18, 2012 12:44 am
- Location: Somerset-West, South-Africa
- Contact:
Re: ZX80 no "K" prompt
C11 was missing! I forgot to put in one tiny 47pF capacitor. I'm such an idiot!
It gives a "K" prompt now. Thanks, everybody for trying to help.
It gives a "K" prompt now. Thanks, everybody for trying to help.
ZX80/ZX81/ZX Spectrum
Re: ZX80 no "K" prompt
The ZX is not so forgiving. Everything has to be in order for the picture to show, because the picture is purely software
Re: ZX80 no "K" prompt
I also won't be happy, if my C5 would be missing ...
forum.tlienhard.com/phpBB3/viewforum.php?f=10
Siggi
My ZX81 web-server: online since 2007, running since dec. 2020 using ZeddyNet hardware
http://zx81.ddns.net/ZxTeaM
http://zx81.ddns.net/ZxTeaM