Zeddy displaying wrong characters on screen

Discussions about Sinclair ZX80 and ZX81 Hardware
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Lardo Boffin
Posts: 2173
Joined: Sat Nov 26, 2016 2:42 am

Re: Zeddy displaying wrong characters on screen

Post by Lardo Boffin »

Moggy wrote: ↑Fri Mar 01, 2024 11:19 pm
Lardo Boffin wrote: ↑Fri Mar 01, 2024 8:58 pm Guess the program!


IMG_5789.jpeg


Running through the ChromaSCART.
10 PRINT "HELLO WORLD"
20 GOTO 10
Close but not quite enough letters! It is

10 PRINT “HELLO SINCLAIR ZX WORLD”
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
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Lardo Boffin
Posts: 2173
Joined: Sat Nov 26, 2016 2:42 am

Re: Zeddy displaying wrong characters on screen

Post by Lardo Boffin »

Moggy wrote: ↑Fri Mar 01, 2024 11:17 pm A cell from a de-capped 2c184 ULA, the second picture is a cell with the overlay from Sinclair.

I've had one or two that partially failed, membrane keyboard presses causing a crash but with a Memotech plugged in all ok.
Replacement of the ULA cured it so not a board fault.
Great photos!

I have ‘The Spectrum ULA - How to Design a Microcomputer’ book - a really good read! If a little hard going in places if you don’t have an electronics background.
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
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msknight
Posts: 386
Joined: Fri Dec 15, 2023 8:26 pm
Location: Sussex, UK

Re: Zeddy displaying wrong characters on screen

Post by msknight »

Yes, it is a bit crazy... we digitise so much analogue stuff only to find that the digital processes are running on an analogue system :-)
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