Refurbing an issue one zeddy

Discussions about Sinclair ZX80 and ZX81 Hardware
Post Reply
Lardo Boffin
Posts: 2256
Joined: Sat Nov 26, 2016 2:42 am

Re: Refurbing an issue one zeddy

Post by Lardo Boffin »

If a zeddy has 16k internal RAM is it just disabled if a RAM pack is plugged in, regardless of the RAM pack size?

Thanks.

Lardo
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
Top
sirmorris
Posts: 2812
Joined: Thu May 08, 2008 5:45 pm

Re: Refurbing an issue one zeddy

Post by sirmorris »

It is disabled by any hardware which ties the !RAMCS line high on the edge connector - as long as the standard ram chip select line is used to enable the new internal chip. The !RAMCS signal connects to the ULA through a resistor, R2, which allows external hardware to pull it high without damaging the ULA.
Top
Lardo Boffin
Posts: 2256
Joined: Sat Nov 26, 2016 2:42 am

Re: Refurbing an issue one zeddy

Post by Lardo Boffin »

Thanks. So as long as I don't get it wrong it will be fine then! I had a panic moment earlier when I tried a suspect RAM pack with my 'being refurbished' zeddy and got no output to TV. This being because I had connected it to the composite out and have not got that far yet... :oops:
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
Top
Lardo Boffin
Posts: 2256
Joined: Sat Nov 26, 2016 2:42 am

Re: Refurbing an issue one zeddy

Post by Lardo Boffin »

1024MAK wrote: ↑Mon Jul 03, 2017 1:02 am Well done :D

Mark

PS, next, the why wait mod? Link #1, link#2, link#3 ;)
Is the process for fitting 16k to an issue three the same as an issue one?

Many thanks!

Lardo
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
Top
User avatar
1024MAK
Posts: 5532
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...
Contact:
Contact 1024MAK

Re: Refurbing an issue one zeddy

Post by 1024MAK »

Answered in a new thread here ;)

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Spring approaching...
Top
Lardo Boffin
Posts: 2256
Joined: Sat Nov 26, 2016 2:42 am

Re: Refurbing an issue one zeddy

Post by Lardo Boffin »

Moved to viewtopic.php?f=7&t=2557
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
Top
User avatar
amigaman07
Posts: 35
Joined: Thu May 04, 2017 6:34 am
Location: Newcastle Australia

Re: Refurbing an issue one zeddy

Post by amigaman07 »

This is all Fascinating Stuff.

You just need a RESET Button now ;)

I recently Up-Graded my "Commodore 16" (Yes, I have a Working 1) to 64Kb of RAM, now it Runs all the Plus4 64K Software, in a Better looking (I think) Commodore 64 Type Case! ;)

Darren (amigaman07)
Top
Lardo Boffin
Posts: 2256
Joined: Sat Nov 26, 2016 2:42 am

Re: Refurbing an issue one zeddy

Post by Lardo Boffin »

I have one of these so fairly close I guess.

https://www.retroleum.co.uk/zx81-peripherals

My wife's C64 has a reset button if that helps.
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
Top
Post Reply

Return to “Hardware”