Sinclair ZX80 / ZX81 / Z88 Forums

dizzy33 wrote: ↑Fri Jan 31, 2020 8:11 am So I think I will buy one from sellmyretro.

Sell My Retro is a trading site with various sellers.

The seller I use for replacement membranes is rwap_software, so this listing for example.

Mark

It may be a clone of a ZX80, in which case, the keyboard looks like this: https://upload.wikimedia.org/wikipedia/commons/2/24/ZX80.jpg Most BASIC key words use the ‘single’ keypress system, apart from some functions where they are entered letter by letter. The ZX80 manual is here (hosted by World of...

:o What! :shock: Who woke me up? :? I’ve not looked at any of the audio files, let alone commented! @8008guy - The original ZX80, ZX81 and ZX Spectrum computers all require an audio ‘volume’ level that is near the limit, or greater than the limit of most current consumer ‘headphone’ / ‘earphone’ out...

Hello and welcome to our forum Olivier! :D :D :D Thanks for maintaining www.old-computers.com . I find it to be a very useful resource. Especially for the less well known machines :D I hope you enjoy the forum :D We are happy to help if you have any questions or would like help with anything Zeddy ...

Lardo Boffin wrote: ↑Tue Jan 28, 2020 8:15 pm Welcome! I also have one or two ZX81s.

Old computers is bookmarked for a later view.

Don’t delay, visit TODAY

[As I often do ]

Mark

No sound
Test and if needed, replace D9, D13 (both 1N4148), TR7 (ZTX650, ZTX651 or ZTX653) and the speaker (40Ω).

Mark

I am worried at the electrical "hum" from the 4A, and the low 12V line (10.8V) - any suggestions appreciated I would not worry much about the hum, it seems that coil's windings became loose. If you think the whine is loud, try an issue 1 or issue 2 board, the coils on these don’t appear to have any...

For the low +12V: Test the +5V rail at the emitter of TR5 to confirm that it is 5V, Switch off and disconnect and remove TR5, Test the value of resistors R59 and R60 (you may have to desolder and lift one leg of one of them), Fit a new transistor in TR5 position. ZTX213 can be replaced with ZTX750 i...

The ZX81 ROM only tests for between 1K and 16K of RAM. It ignores RAM below 0x4000 and ignores RAM above 0x8000. Just to save future questions from other members, please keep in mind that the program in the above post is only suitable if there is real RAM between 32768 (0x8000) and 65535 (0xFFFF). I...

The ZX Spectrum +2 (grey case and uses a 2.1mm / 5.5mm barrel power plug) uses a “Sinclair 128K Spectrum +2 Power Supply Unit” rated at 9V DC at 2.1 Amps. This is also in a grey case. The PCB in the ZX Spectrum +2 has on board power supply circuitry. This produces a +5V DC rail, a +12V DC rail and a...