Search found 688 matches

by mrtinb
Fri Jul 20, 2018 10:02 am
Forum: SALES
Topic: ZX81 ULA
Replies: 48
Views: 1875

Re: ZX81 ULA

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.
by mrtinb
Fri Jul 20, 2018 7:06 am
Forum: SALES
Topic: ZX81 ULA
Replies: 48
Views: 1875

Re: ZX81 ULA

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

I’ll debug with my digital probe then. :)
by mrtinb
Thu Jul 19, 2018 12:42 pm
Forum: SALES
Topic: ZX81 ULA
Replies: 48
Views: 1875

Re: ZX81 ULA

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...
by mrtinb
Thu Jul 12, 2018 9:33 am
Forum: Hardware
Topic: ZX81 rebuild
Replies: 124
Views: 7645

Re: ZX81 rebuild

Lardo, are you planning to get in the World's Book of Records with owning most ZX81s?
by mrtinb
Tue Jul 10, 2018 10:37 pm
Forum: Hardware
Topic: Half dead 8300
Replies: 3
Views: 210

Re: Half dead 8300

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...
by mrtinb
Tue Jul 10, 2018 10:31 pm
Forum: Hardware
Topic: Half dead 8300
Replies: 3
Views: 210

Re: Half dead 8300

Is it a ULA from a Lambda or a ZX81 you have swapped in?
by mrtinb
Tue Jul 03, 2018 9:22 pm
Forum: SALES
Topic: ZX81 ULA
Replies: 48
Views: 1875

Re: ZX81 ULA

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...
by mrtinb
Mon Jul 02, 2018 10:01 am
Forum: Development
Topic: A Nebulus clone/adaptation???
Replies: 2
Views: 88

Re: A Nebulus clone/adaptation???

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.
by mrtinb
Thu Jun 28, 2018 6:58 pm
Forum: SALES
Topic: ZX81 ULA
Replies: 48
Views: 1875

Re: ZX81 ULA

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