Hi.
New here, but I've been active on other forums (Stardot, SpectrumComputing, Defence-Force) for some time now and i recognise some of the names on here.
I have an early issue 1 ZX81, which i bought last year. It's in beautiful condition, one owner and hardly used. I'd never opened it, and It worked perfectly until the other day.
I bought a MemoPak 16kb in mint condition, "tested and working" and when, i recieved it, i fitted it to the zx81, and powered up. Nothing. turned it off and unplugged it, turned the ZX81 on, nothing, apart from the band on the picture below.
I'm not sure what has happened, but i want to get this little fella up and running without losing its originality if possible.
so far, i've checked voltages to the ram and the ULA and they are 4.92v, current draw is around 300ma, done the touch test, and nothing is getting hot. I've set my scope up so that's the next step (once i've done the jobs im supposed to do and released back into my cave).
any suggestions you can provide would be great. thanks.
Poorly ZX81
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Poorly ZX81
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
-
- Posts: 3
- Joined: Sat Jun 06, 2020 12:51 pm
-
- Posts: 3
- Joined: Sat Jun 06, 2020 12:51 pm
Re: Poorly ZX81
A7 at the ROM
The Luma signal going into the Modulator
Re: Poorly ZX81
My expertise in all things tecchy is zilch and I know the following is anecdotal, but just about every blown ULA (including the new replacements) I have suffered has been down to a duff or failing Memotech memory pack.
I'm the klutz who couples/uncouples things when powered up and manage to get away with it with just about any other add on but plug in a failing memopack with power off then switched on and it's goodnight Vienna for Mr ULA.
I'm the klutz who couples/uncouples things when powered up and manage to get away with it with just about any other add on but plug in a failing memopack with power off then switched on and it's goodnight Vienna for Mr ULA.
Re: Poorly ZX81
I am happy that you finally got yout [K] on this ZX81..
We met at Facebook...
one of mine s still hasn't seen the light
Ernesto
We met at Facebook...
one of mine s still hasn't seen the light
Ernesto
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Poorly ZX81
Apart from the hassle of work and trying to cope with hey fever, I’m fine. Not looking forward to wearing a mask at the same time as having bad hey fever though
Yeah, but I wouldn’t mind if you were a pretty woman in a short skirt
From what I can tell, the logic levels on the digital signal lines look okay. The Z80 looks like it’s running. You definitely don’t have any actual video signal though, your ‘scope image looks like just random noise.
Test A14 and A15 to see if the Z80 is actually trying to generate a screen display.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.