The startup black screen/coloured garbage is an artifact of the fact that the Spectrum shared display memory with main ram. It should be vaguely a black screen, perhaps with the odd coloured cell, but should disappear within a second or thereabouts and give you the Sinclair Research prompt.

Lots of Spectrums have keyboard faults - almost always the membranes and/or the ribbon cable, like you've found out.

The later 48k+ and 128K machines have better (and more robust) keyboards, but they're all fragile to a certain degree - the RAM chips often go, and the expansion port is directly tied to the Z80, so it's easy to damage the processor if the peripheral is not connected properly or accidentally removed whilst powered on.

That said, as with a lot of early 80's machines there are now loads of modern updates for them: native HDMI or VGA out, audio upgrades, flash memory storage etc.

megatron-uk wrote on 2021-01-27, 19:53:

The startup black screen/coloured garbage is an artifact of the fact that the Spectrum shared display memory with main ram. It s […]
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The startup black screen/coloured garbage is an artifact of the fact that the Spectrum shared display memory with main ram. It should be vaguely a black screen, perhaps with the odd coloured cell, but should disappear within a second or thereabouts and give you the Sinclair Research prompt.

Lots of Spectrums have keyboard faults - almost always the membranes and/or the ribbon cable, like you've found out.

The later 48k+ and 128K machines have better (and more robust) keyboards, but they're all fragile to a certain degree - the RAM chips often go, and the expansion port is directly tied to the Z80, so it's easy to damage the processor if the peripheral is not connected properly or accidentally removed whilst powered on.

That said, as with a lot of early 80's machines there are now loads of modern updates for them: native HDMI or VGA out, audio upgrades, flash memory storage etc.

Thanks so much for the reply.

The startup screen does disappear pretty quickly. It varies between almost solid black and black stripes with coloured artifacts, but it disappears very quickly so I guess that's normal? After that the standard Sinclair Research prompt shows up.

So I guess its worth my while to buy a replacement membrane then? Don't really know what I'll be doing with the machine in the long run, but I also don't want it to end up collecting dust in my cupboard as it did with the previous owner.

The device itself is in great shape. It came in its box with the original power supply and AV cable. It looks almost new.

Totempole wrote on 2021-01-27, 20:40:

[...]

Thanks so much for the reply.

The startup screen does disappear pretty quickly. It varies between almost solid black and black stripes with coloured artifacts, but it disappears very quickly so I guess that's normal? After that the standard Sinclair Research prompt shows up.

If it's completely white (well, as close to white as you get with crappy modulated composite...) with black text, then yes, it's normal.

So I guess its worth my while to buy a replacement membrane then? Don't really know what I'll be doing with the machine in the long run, but I also don't want it to end up collecting dust in my cupboard as it did with the previous owner.

The device itself is in great shape. It came in its box with the original power supply and AV cable. It looks almost new.

Not bad. Yes, membranes aren't too expensive and (along with the cable) are indeed first things to go.

If you've never had a Speccy before, don't be surprised at how truly crappy the keyboard really is. There's a reason there was such a big aftermarket for better ones. I'm contemplating building myself a Spectrum 128 kit. After finding that 128 or + cases in good nick are viciously expensive, and faced with the option of building it into a 48k rubber beermat, I went and bought a Cherry MX-compatible keyboard PCB for Spectrum. I suffered through most of the 1980s on Sinclair keyboards, despite a lot of nostalgia, I don't want to suffer like that again.

I was fortunate enough that my first computer was the 48K+ with the QL-style plastic keys. All my friends had the original dead-flesh rubber key model... oh my that was horrible. Calculator keys on a computer!

I got through several of these things back in the day. I had one with a similar problem to the OP. I never fixed it, but worked around the problem by unscrewing the case, pulling the keyboard forward, and resting it at an angle against the base. They keys worked fine then. Clearly, stretching the ribbon cable restored a broken connection somewhere.

I've confirmed beyond any doubt that it is definitely a faulty membrane. I used probes to input key commands using the membrane as a map and it responds perfectly fine.

It's not that I doubted the membrane was an issue, I just wanted to make sure that there wasn't something more serious wrong with it.