Fixing inherited Sinclair ZX81

[1024MAK]

So the internal series regulators in the ULA are working (that generates a lot of the heat), but it looks like the clock / oscillator stages may not be working.

So yes, it’s dead unfortunately.

Mark

[mikeyp]

Right, thank you. Sad as it is, this is positive news though. I now have a diagnosis and have therefore ordered a vLA81 and a socket.

I shall set to (carefully) desoldering the old ULA and will report back with my results once the vLA81 arrives and is installed.

Thank you again. I shall check in in a few days.

[mikeyp]

Old ULA removed in readiness.

[mikeyp]

It’s alive! Thank you for all your help!

[1024MAK]

That’s good news

Mark

[Moggy]

Another one lives well done Mikeyp.

Add a switching reg to it and it will run a damn sight cooler and should last for ages.

[mikeyp]

Another one lives well done Mikeyp.

Add a switching reg to it and it will run a damn sight cooler and should last for ages.

I was thinking about that. Any particular recommendations?

[1024MAK]

I use Recom types (because I bought a load when the price was low), as detailed (and shown) in this topic. But other similar types like from Traco Power and MuRata are fine as well.

Mark

[AN7805]

Are not dangerous for the vLA81 using the RF?
Or is possible?

Thanks,

Matt

[mikeyp]

I use Recom types (because I bought a load when the price was low), as detailed (and shown) in this topic. But other similar types like from Traco Power and MuRata are fine as well.

Mark

Thanks, I'll see what I can find.

Are not dangerous for the vLA81 using the RF?
Or is possible?

Thanks,

Matt

It shouldn't be a problem as the modulator only takes composite output and modulates it to RF. There's no mention of that on the website or manual. I configured mine to output the same as a 2C210E. I've had no issues with the display, modulator or the old black and white RF only TV I'm using.