Search found 9 matches

by hjalfi
Mon Sep 24, 2018 11:10 am
Forum: Sinclair Misc
Topic: Live coding on a ZX81
Replies: 1
Views: 1918

Live coding on a ZX81

Now that my shiny new ZX81 is renovated and working, I made a terrible video of me livecoding a game on it. Enjoy.

https://www.youtube.com/embed/WqVfyyZbIvo

(Does this version of phpbb have video embedding disabled?)
by hjalfi
Tue Sep 11, 2018 9:53 pm
Forum: Hardware
Topic: ZX81 essential maintenance?
Replies: 21
Views: 3483

Re: ZX81 essential maintenance?

Red PCB, checksum is 855106, back porch present, so it's indisputably the new ULA and the new ROM. Re black level: yes, you're right, I misread the spec. So about the only thing I can think of which the HDMI upscaler is upset about could be that the sync pulse is at 0V rather than -0.4V? But it's su...
by hjalfi
Tue Sep 11, 2018 11:05 am
Forum: Hardware
Topic: ZX81 essential maintenance?
Replies: 21
Views: 3483

Re: ZX81 essential maintenance?

I believe it's the later model of ULA, but like an idiot I forgot to photograph the board the last time I had it open, and I'm a bit hesitant to do so again without good cause (it's a miracle the keyboard tails still work as it is). Judging by the oscilloscope trace a back porch of about 2.5V is bei...
by hjalfi
Mon Sep 10, 2018 5:41 pm
Forum: Hardware
Topic: ZX81 essential maintenance?
Replies: 21
Views: 3483

Re: ZX81 essential maintenance?

So... the long delay in response is because I was waiting for hardware to arrive. I built Mark's circuit; it worked fine on the Sony monitor, with a nice crisp image. No luck on the TV, and absolutely nothing on the composite video capture card or the HDMI converter. So I ordered Pokemon's board, wh...
by hjalfi
Wed Aug 22, 2018 11:29 pm
Forum: Hardware
Topic: ZX81 essential maintenance?
Replies: 21
Views: 3483

Re: ZX81 essential maintenance?

Woohoo, it all works! It'll even load and save, although it won't load the four commercial ZX81 games I have (Psion Flight Simulator, QS Defenda, JD Arcades, and Adventure C: The Ship Of Doom); but this could be anything from cassette tracking problems to the 16kB rampack not working properly on a 9...
by hjalfi
Tue Aug 21, 2018 11:35 pm
Forum: Hardware
Topic: ZX81 essential maintenance?
Replies: 21
Views: 3483

Re: ZX81 essential maintenance?

Well, it's all arrived --- I haven't powered it up yet, though. One of the keys on the keyboard has a pinhole through it, so I'll have to see if it works. I suspect an order from sellmyretro is in my near future. (It came with an almost untouched manual, Sinclair product catalogue and ZX81 flyer, an...
by hjalfi
Tue Aug 21, 2018 4:18 pm
Forum: Hardware
Topic: ZX81 essential maintenance?
Replies: 21
Views: 3483

Re: ZX81 essential maintenance?

Hmm. Okay, I'll try it and see. Would 12V be safe? As I have lots of power supplies which generate 12V. (However, I don't think I want to hook up a 12V power supply until I've had a chance to replace the 5V linear regulator, because it would get seriously hot.) (Speaking of which, I have some stick-...
by hjalfi
Tue Aug 21, 2018 11:44 am
Forum: Hardware
Topic: ZX81 essential maintenance?
Replies: 21
Views: 3483

Re: ZX81 essential maintenance?

Good to know. I plan to admire the outside of the 9V supply and then put it on a shelf somewhere. Old computers are interesting; old and rather dubious unregulated mains power supplies with rotting electrolytic capacitors are not. I've got a modern 9V switch mode for this. (When I tried Ihe power su...
by hjalfi
Tue Aug 21, 2018 10:24 am
Forum: Hardware
Topic: ZX81 essential maintenance?
Replies: 21
Views: 3483

ZX81 essential maintenance?

My new ZX81 with 16kB Memopak arrives today. Huzzah! Before I apply power, is there any work I should do on the board? For example: I know that you shouldn't power up an original Spectrum without recapping, because capacitor failure in the power regulator can cause the wrong DRAM voltage, resulting ...