Search found 5102 matches

by 1024MAK
Wed Mar 13, 2024 3:21 pm
Forum: Hardware
Topic: Spectrum modded / composite question
Replies: 19
Views: 710

Re: Spectrum modded / composite question

ULAs seem harder to come by. Original 'spare' ULA chips ran out years ago. Only used ULAs come up occasionally. However, there are replacement ULA modules. But they are in a limited supply, and are not cheap. Nebula - Scroll down on this page . vLA82 - link From my understanding I'd need a clear vi...
by 1024MAK
Wed Mar 13, 2024 1:10 pm
Forum: Hardware
Topic: ZX81 RAM compatibility for replacement
Replies: 1
Views: 135

Re: ZX81 RAM compatibility for replacement

The MCM21L14P30 is a low power version of the MCM2114. The MCM21L14P30 has a maximum access time of 300ns NOT 30ns. The MCM21L14P45 has a maximum access time of 450ns NOT 45ns. A data sheet for these is available here Any 2114 SRAM chip with a maximum access time of 300ns or quicker should work incl...
by 1024MAK
Tue Mar 12, 2024 11:53 pm
Forum: Hardware
Topic: Spectrum modded / composite question
Replies: 19
Views: 710

Re: Spectrum modded / composite question

If you hear the key click sounds and BASIC appears to be running (try SAVE "P" ), then it's more likely to be a ULA fault rather than a DRAM fault. But without a test/diagnostic ROM or another ULA to swap with, it's hard to be certain.

Mark
by 1024MAK
Tue Mar 12, 2024 1:40 pm
Forum: Hardware
Topic: Spectrum modded / composite question
Replies: 19
Views: 710

Re: Spectrum modded / composite question

In answer to the chips in sockets, your machine was sold as a 16K RAM model. The chips in sockets have been added later. It was normal for Sinclair to fit sockets for the extra chips needed for the 48K RAM option. Does the border always turn white at every power on? Do this (power cycle waiting 30 s...
by 1024MAK
Mon Mar 11, 2024 9:30 pm
Forum: Hardware
Topic: Spectrum modded / composite question
Replies: 19
Views: 710

Re: Spectrum modded / composite question

Hello and welcome Elfish I'd really like to get that thing running for my dad and I read a lot about composite mods. I came across the ZX8-CCD PCB. Anyone knows if the board is also compatible with the board and ULA? The ZX8-CCD is only designed for use with monochrome video, that is, for use with a...
by 1024MAK
Sun Mar 10, 2024 11:01 am
Forum: Hardware
Topic: When is the 10K RAM resistor needed?
Replies: 4
Views: 278

Re: When is the 10K RAM resistor needed?

People are following the details that are widely available on the internet, even though those details are slightly misleading.

Mark
by 1024MAK
Sun Mar 10, 2024 10:59 am
Forum: Hardware
Topic: RAM speed issue
Replies: 29
Views: 1111

Re: RAM speed issue

It is possible that not all original Ferranti ULA chips would have worked correctly with WRX hires graphics software. Remember, the hardware was not designed for this. With the wide variety of components used (different makes/models/manufacturers of processors, RAM, ROM, the different ULA versions a...
by 1024MAK
Sun Mar 10, 2024 10:39 am
Forum: Hardware
Topic: When is the 10K RAM resistor needed?
Replies: 4
Views: 278

Re: When is the 10K RAM resistor needed?

Are you using battery back up? If no, then the 10kΩ resistor between pins 27 and 28 is not needed. Pin 27 will always be driven by the Z80 /WR control line. This is not true however if the RAM is being powered by a backup battery, in which case, the battery supply (pin 28) would need to pull-up pin ...
by 1024MAK
Sat Mar 09, 2024 8:29 am
Forum: Welcome Area
Topic: Hello everyone, I'm new here
Replies: 1
Views: 335

Re: Hello everyone, I'm new here

Translated to English: Hi everyone, I'm new here. I have always had a passion for electronics in general. Taking up my ZX80 I wanted to reconstruct it, I see a lot of information on it online, but I'm not a good programmer. I studied the Z80 35 years ago, I remember little. Thanks to you I discovere...
by 1024MAK
Fri Mar 08, 2024 8:37 pm
Forum: Hardware
Topic: RAM speed issue
Replies: 29
Views: 1111

Re: RAM speed issue

It's extremely unlikely that TR1 is causing an issue. Transistors in circuits like this are not under any stress whatsoever, and transistors are fairly hardy and reliable devices. I'm sorry that I can't help you much. But with edge cases especially when it comes to timing issues, they can be extreme...