Sinclair ZX80 / ZX81 / Z88 Forums

I have a Siglent SDS 1202X-E two-channel 200Mhz scope and it has been ideal for diagnosing and repairing my Atari, Commodore and now Sinclair machines. After using it regularly for over 2-1/2 years, I have zero complaints.

The real Zeddy experts will weigh in here soon, I’m sure, but to set the background: do you have experience generally with vintage electronics hardware diagnosis and repair procedures? Much of the basics will be the same across system architectures. Since you don’t know of the system was working, st...

Try adding an extra capacitor. Add a ceramic type (or better yet, a multilayer ceramic type) and connect it between the existing connections for C2 on the underside of the board, and/or add a capacitor (again a ceramic type) between pins 34 and 40 of the ULA socket (IC1) again on underside of the b...

So I finished the composite board for the TS1000 today and - after realizing I’d installed the BC548 backwards (D’oh!), I get a nice sharp image. Unfortunately, and unlike my ZX81, I’m getting jailbars. Drat. Where’s the most likely source of noise on this style of board? I have plenty of .1uF ceram...

I would definitely replace the 7805 if you are going to use it a lot. It makes a huge difference. Yep. I already did the same with my ZX81. I used a Traco TSR 1-2450. It’s a tight (very tight!) fit against the corner of the case top, but it fits, if only barely. If I were to buy more of these speci...

The quality or rather, lack of, of the RF TV output is very much determined by the modulator, and how good the TV is at tuning to the actual carrier frequency produced by the modulator. … Indeed. I’ve got lots of (too much!) experience with crappy or marginal RF from vintage consoles and computers,...

Which version ULA was the one you swapped it with? Same as what was in it. I was looking to see if the output quality difference was due to a variation in the specific chips. It wasn't - the RF modulator on the TS1000 just made a worse image than the modulator from the ZX81. That's why I decided to...

Which ULA does it have? The same as in my ZX81, the 2C184E. This on was made in the 10th week of '82 per the date code (that one was made in the 26th week of '82). I swapped ULAs to see if the RF would improve but sadly, it didn't. So I've already removed and gutted the RF can and have one of your ...

With the bottom off, I see the nice red finish I'd expect of an Issue 3, like the US-market ZX81 I got a few months ago. However, the layout - despite being machine-routed, looks like an Issue 1. Flip it over and huh, it says "Issue 1" right on the silkscreen, despite being machine-routed. So my fir...

Very cool. Reminds me a great deal of Chris Crawford's excellent early Atari Program Exchange title, SCRAM. I will give this a try this weekend.