Zx81 composite mod with backporch-Advice
Re: Zx81 composite mod with backporch-Advice
As it is a day I cannnot go out because of storm Barbara here in Greece, I've finally got around to opening up my ZX81 it fit a composite mod. Here's some pictures of opening up my first computer.
I'm curious to know about the serial number on the outside of the box. By the looks of these it confirms I got it November 1982. 1980 circuit board
I'm curious to know about the serial number on the outside of the box. By the looks of these it confirms I got it November 1982. 1980 circuit board
ZX81 (purchased November 1982), my first computer.
ZXpand+, ZX8-CCB.
ZXpand+, ZX8-CCB.
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Re: Zx81 composite mod with backporch-Advice
I can see some of the date codes, definitely made in 1982. Looks like week 6 or later, so likely spring 1982.
Oh, and it looks the all the chips are in sockets. It’s very unusual for factory made boards to have the RAM in sockets.
Mark
Oh, and it looks the all the chips are in sockets. It’s very unusual for factory made boards to have the RAM in sockets.
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.
Re: Zx81 composite mod with backporch-Advice
And the reluctant keyboard connector looks intact.
Thinking of mounting the ZX8-CCB on top of the rf modulator. I saw this done in a youtube video.ZX81 (purchased November 1982), my first computer.
ZXpand+, ZX8-CCB.
ZXpand+, ZX8-CCB.
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Re: Zx81 composite mod with backporch-Advice
You can also mount them quite neatly underneath the motherboard:
And then just run the brown wire round to the RF can:
This way if you find you need to adjust the pots after fitting the keyboard it is much easier to do so as you won’t have to detach the motherboard from the top case.
I find it easier to adjust the pots when there is a reasonable amount of text on the screen.
And then just run the brown wire round to the RF can:
This way if you find you need to adjust the pots after fitting the keyboard it is much easier to do so as you won’t have to detach the motherboard from the top case.
I find it easier to adjust the pots when there is a reasonable amount of text on the screen.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Re: Zx81 composite mod with backporch-Advice
Something is not right.
Gave the power socket a quick spray with contact cleaner as it was not making good contact.
Checked the 5v power line with my ancient 80's cheap meter, seems ok.
Had a good visual look to see if I made solder bridges, don't see any.
Any ideas?
Here's my poor soldering:
I cleaned up with 95% alochol. Gave the power socket a quick spray with contact cleaner as it was not making good contact.
Checked the 5v power line with my ancient 80's cheap meter, seems ok.
Had a good visual look to see if I made solder bridges, don't see any.
Any ideas?
Last edited by rmbrowngr on Sun Feb 05, 2023 4:42 pm, edited 1 time in total.
ZX81 (purchased November 1982), my first computer.
ZXpand+, ZX8-CCB.
ZXpand+, ZX8-CCB.
Re: Zx81 composite mod with backporch-Advice
Could you please add a wire to the second GND Pad of the PCB?
Mine didn't work without both connected.
Mine didn't work without both connected.
In theory, there is no difference between theory and practice. But, in practice, there is.
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Re: Zx81 composite mod with backporch-Advice
I always disconnect both of the two wires going into the RF modulator:
Last edited by Lardo Boffin on Sun Feb 05, 2023 4:48 pm, edited 1 time in total.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
-
- Posts: 2169
- Joined: Sat Nov 26, 2016 2:42 am
Re: Zx81 composite mod with backporch-Advice
Also the position of the pots can have a serious effect on the picture. My start point for adjusting for all but the earliest ULAs is:
Take a photo of where it is now so you can always revert if necessary!
Take a photo of where it is now so you can always revert if necessary!
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Re: Zx81 composite mod with backporch-Advice
First thing i did.Lardo Boffin wrote: ↑Sun Feb 05, 2023 4:44 pm I always disconnect both of the two wires going into the RF modulator:
ZX81 (purchased November 1982), my first computer.
ZXpand+, ZX8-CCB.
ZXpand+, ZX8-CCB.
Re: Zx81 composite mod with backporch-Advice
Yes, all the IC's are socketed.
ZX81 (purchased November 1982), my first computer.
ZXpand+, ZX8-CCB.
ZXpand+, ZX8-CCB.