Search found 2195 matches

by 1024MAK
Mon Jan 21, 2019 8:36 pm
Forum: SALES
Topic: A Gaggle of ZX81's for sale
Replies: 8
Views: 1636

Re: A Gaggle of ZX81's for sale

Hello Kai

Welcome to our forum :D

You may wish to pop over to the welcome area and say hello to everyone ;)

Please do look around, there is lots of useful information, and most importantly, a friendly bunch of members here.

Mark
by 1024MAK
Sun Jan 20, 2019 10:53 am
Forum: Hardware
Topic: Broken +3
Replies: 5
Views: 59

Re: Broken +3

Thinking about it, I’m sure that at least one intermittent fault has been reported where the gate array was suspected, but it was found to be a dry solder joint on one of the gate array pins. Worth checking.

Mark
by 1024MAK
Sun Jan 20, 2019 10:49 am
Forum: Hardware
Topic: Broken +3
Replies: 5
Views: 59

Re: Broken +3

If yes, enter

Code: Select all

CLEAR 32000
You can then see if it will run in 16k “mode” where only the contended DRAM is used.

Most of the time, failure of this DRAM will result in some screen corruption.

Mark
by 1024MAK
Sun Jan 20, 2019 10:45 am
Forum: Hardware
Topic: Broken +3
Replies: 5
Views: 59

Re: Broken +3

Can you get to the “48k” mode by entering

Code: Select all

PRINT USR 0 
from 128k BASIC?

Mark
by 1024MAK
Sun Jan 20, 2019 10:30 am
Forum: Hardware
Topic: Broken +3
Replies: 5
Views: 59

Re: Broken +3

The Amstrad gate array chip controls all the DRAM chips. If it’s this, that’s it, unless you can find a spare... (I don’t know of anyone who has spares). So best concentrate on the DRAM chips. However, you have renewed IC3 and it’s made no difference... :? The schematic is here Notice that there are...
by 1024MAK
Sun Jan 20, 2019 1:27 am
Forum: Hardware
Topic: Fuller FD42 Keyboard
Replies: 64
Views: 5957

Re: Fuller FD42 Keyboard

For simple reverse polarity protection, a 1N400x diode will do (where 1N400x means any from the 1N4001 to 1N4007 series). So that any 9V PSU, of either polarity will work, you need a bridge rectifier. Either a ready made one, or four 1N400x diodes connected up correctly. Rubber key ZX Spectrums are ...
by 1024MAK
Thu Jan 10, 2019 8:22 pm
Forum: Hardware
Topic: Help in resurrecting my ZX81
Replies: 64
Views: 7015

Re: Help in resurrecting my ZX81

Good to hear that you have got your ZX81 working.

That board does look it has been through the wars though...

Mark
by 1024MAK
Wed Jan 09, 2019 11:38 pm
Forum: Hardware
Topic: Best solution for expanding ram to 128k on a zx48k?
Replies: 17
Views: 1229

Re: Best solution for expanding ram to 128k on a zx48k?

Video RAM is the RAM used by the ULA (or gate array) to produce the video picture. In a ZX Spectrum 16k or 48k, this is always the same area of RAM in the “lower” RAM chips, that is, the 4116 chips (eight 16k chips each one bit wide). The 128k machine (and later machines) have 128k chips. The logic ...
by 1024MAK
Wed Jan 09, 2019 4:28 pm
Forum: Hardware
Topic: Best solution for expanding ram to 128k on a zx48k?
Replies: 17
Views: 1229

Re: Best solution for expanding ram to 128k on a zx48k?

Paul wrote:
Wed Jan 09, 2019 12:02 pm
My programmer is a tl866
I use latest lattice settings without problems.
I am not sure whether I have a deviceID check disabled or if it's on defaults.
Kind regards Paul
Thanks Paul :D

Mark
by 1024MAK
Wed Jan 09, 2019 4:27 pm
Forum: Hardware
Topic: Best solution for expanding ram to 128k on a zx48k?
Replies: 17
Views: 1229

Re: Best solution for expanding ram to 128k on a zx48k?

Before I explain further, a bit of history and a time line. Sinclair’s engineering staff developed the ZX Spectrum 16k and 48k machine’s based on what they had learned in creating the ZX80 and ZX81. The ZX Spectrum+ is just a 48k board (or a 16k board) in a new case with a slightly better keyboard. ...