Zeddy displaying wrong characters on screen
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- Posts: 2183
- Joined: Sat Nov 26, 2016 2:42 am
Zeddy displaying wrong characters on screen
I got a zeddy and it does this:
https://www.sinclairzxworld.com/viewtop ... 578#p54578
When you type using either the built in keyboard or my Memotech keyboard it does not show all of the characters you are typing correctly.
If I connect a Spand or a 16K memopak after a very short while it works fine. It starts out showing some characters slightly incorrectly but then they fully form.
Given that the Spand effectively replaces the ROM and RAM I have replaced both of these but it makes no difference.
https://www.sinclairzxworld.com/viewtop ... 578#p54578
When you type using either the built in keyboard or my Memotech keyboard it does not show all of the characters you are typing correctly.
If I connect a Spand or a 16K memopak after a very short while it works fine. It starts out showing some characters slightly incorrectly but then they fully form.
Given that the Spand effectively replaces the ROM and RAM I have replaced both of these but it makes no difference.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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- Posts: 2183
- Joined: Sat Nov 26, 2016 2:42 am
Re: Zeddy displaying wrong characters on screen
The fact that it also works with a 16K ram pack but not without would point to the RAM being faulty somehow but replacing it made no difference.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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- Posts: 2183
- Joined: Sat Nov 26, 2016 2:42 am
Re: Zeddy displaying wrong characters on screen
This is what I get when I type all of the keys:
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Re: Zeddy displaying wrong characters on screen
Nothing stuck in the keyboard sockets are there? Have you tried removing the keyboard and just using the memotech?
All that I've learned - https://msknight.com/bbc/index.html#zx81
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- Posts: 2183
- Joined: Sat Nov 26, 2016 2:42 am
Re: Zeddy displaying wrong characters on screen
I will check inside the keyboard sockets just in case but it does the same with just the Memotech keyboard connected.
It loads and plays the games that I have tried. Although the screen is suitably garbled.
It loads and plays the games that I have tried. Although the screen is suitably garbled.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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- Posts: 5153
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Zeddy displaying wrong characters on screen
Don't forget, with 16K bytes of RAM, you get a fully expanded display file, and it can be in a different position in RAM.
Have you tried changing the ULA?
Mark
Have you tried changing the ULA?
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.
Re: Zeddy displaying wrong characters on screen
I recall, along time ago, that I had a similar problem and replacing the voltage regulator fixed the problem. I got this idea from a forum posting but I can't find it. Not being a hardware guy I have no idea why the voltage regulator would garble the display, but replacing it worked for me.
Regards from Hardware Challenged;
Greg
Regards from Hardware Challenged;
Greg
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- Posts: 2183
- Joined: Sat Nov 26, 2016 2:42 am
Re: Zeddy displaying wrong characters on screen
I will be looking for a spare later on thanks.
If I type in a program that takes up most of the 1K and it doesn’t corrupt would that prove the RAM is ok?
I did replace the 1K RAM with chips that were working a while back but this is the only socketed zeddy I currently have.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Re: Zeddy displaying wrong characters on screen
I'm taking that it came to you like this, and has never worked. Yes?
If that's the case, first thing would be to check for shorts and breaks on the data lines. But I take it you've already done this.
If that's the case, first thing would be to check for shorts and breaks on the data lines. But I take it you've already done this.
All that I've learned - https://msknight.com/bbc/index.html#zx81
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- Posts: 2183
- Joined: Sat Nov 26, 2016 2:42 am
Re: Zeddy displaying wrong characters on screen
It arrived like this yesterday. Sold as untested (as usual).
I haven’t had time to get technical yet - just a few minutes to try some high level stuff at lunch time.
Hopefully when the kids are in bed…
I haven’t had time to get technical yet - just a few minutes to try some high level stuff at lunch time.
Hopefully when the kids are in bed…
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA