Sinclair ZX80 / ZX81 Forums

TMAOne wrote: ↑

Fri Jul 20, 2018 7:34 am

What you might want to spend a couple of bucks for is one of those cheap Chinese knock off Logic Analyzers. USB hookup to your computer, free software, and 8 channels at 24 MHz. They're great fun too.

That's a great idea. Thanks.

I see your point. The oscilloscope has to be faster than the circuit it measures. (I know people say these oscilloscopes were bad, but now I know why.)

I’ll debug with my digital probe then.

So tonight I repaired the PCB which had been damaged in the ULA removal process. And added the 1K resistor and ground to the ULA to get it working through the modulator. Unfortunately it's an unstable gray screen so something has changed. Debugging will continue when I receive my cheap oscilloscope...

That was a great listen. Thank you

Lardo, are you planning to get in the World's Book of Records with owning most ZX81s?

Sorry! Stupid question. Since you have characters on the screen it is a ULA from a Lambda. (Since the characters on the Lambda is inside the ULA and not the ROM) But when you have a working Lambda you can insert the CPU and ULA in there and measure all IC pins on all ICs with eighter voltmeter, digi...

Is it a ULA from a Lambda or a ZX81 you have swapped in?

Mine arrived today. The ULA was for repair of my first ZX81 imported from the Danish company ZXdata. I have had it working and shortly after joining this forum it broke with white screen. The conclusion back them was the ULA must be broken. I had a digital probe to test with. Since then I used a lot...

You can start to see if it works on the ZX81 with the Sponzy ROM (that supports some Spectrum programs).

Maybe you could use most of the codebase. There's not much color in the Spectrum version.

We haven’t got a replacement ULA for years, so you came at the right time. Wait a week and there will be more.