Sinclair ZX80 / ZX81 / Z88 Forums

Hello,

my dad recently took me into his basement to show off some old stuff.
He bought a Sinclair Spectrum back in the early 80s and modded the shit out of it.
His words were.

The original keyboard was crap, I had to do something about it.

He basically took some old keyboard and used this behemoth as a housing and added some extras.
The housing is very heavy and made from metal. The walls are like 4-5 mm thick.
The old keyboard keys were used to build a custom keyboard including all the wiring.
A long with the custom keyboard there are a couple extra switches and an amplifier pcb for an extra internal speak, that is powered by a 9V battery.
The housing also includes the power supply for the Spectrum.
There is a switch that says save and load. I can only guess what it does. I assume this switches the mic and ear output so the cables don't need to be switches physically when reading or writing from or to a cassette? Apparently the cassette player supports remote start and stop. Amazing!
The Spectrum itself is a issue two board with a 5C112E-3 ULA.

I'd really like to get that thing running for my dad and I read a lot about composite mods. I came across the ZX8-CCD PCB. Anyone knows if the board is also compatible with the board and ULA?

Hello and welcome Elfish

Elfish wrote: ↑Mon Mar 11, 2024 8:39 pm I'd really like to get that thing running for my dad and I read a lot about composite mods. I came across the ZX8-CCD PCB. Anyone knows if the board is also compatible with the board and ULA?

The ZX8-CCD is only designed for use with monochrome video, that is, for use with a ZX80, ZX81, TS1000 or similar machines.

For a ZX Spectrum, there are various so called composite video modifications. I suggest you try the capacitor version.

You only need one part: one 100µF 16V electrolytic capacitor. Only buy from a reputable supplier.

On the ZX Spectrum PCB, locate the modulator. It's the large metal can that has the TV aerial output socket on it. Using a flat bladed screwdriver, carefully prise the lid off.

At the side of the ZX Spectrum PCB you should see two wires coming out of the modulator and going to the ZX Spectrum PCB. Using a soldering iron, carefully melt the solder so that you can gently (with very little force) pull each of the wires out of the solder pads on the board. Do not use force, otherwise you will rip the though-hole plating and the PCB track pads off the board.

Coil these up and secure them so that they cannot come loose and cause problems.

Inside the modulator, you will see the lead of a resistor soldered to the centre pin of the TV aerial output socket. This needs disconnecting. Once disconnected, move it clear so that it cannot touch the centre pin of the TV aerial output socket.

The 100µF 16V electrolytic capacitor is going to go outside the case of the modulator. Now feed through the negative lead (the lead next to the - minus markings) of the 100µF 16V electrolytic capacitor through the spare left hand plastic hole in the modulator so that it goes to the centre pin of the TV aerial output socket. Trim it to length and then solder it in place.

Connect the other (positive) capacitor lead into the nearby solder pad (the one that the left hand wire to the modulator came out of) after cutting it to a suitable length, then solder it in place.

Refit the lid of the modulator.

Now stick a reminder label on the computer to say that it's now a composite video output. And of course, test it works!

See also this web page

Please note that this works okay with most TVs, but not all. If it does not work, please do try another TV.

Mark

I see it's got the same 48K memory upgrade that my S2 has. Note the extra little green PCB that allows for OKI DRAM

1024MAK wrote: ↑Mon Mar 11, 2024 9:30 pm The 100µF 16V electrolytic capacitor is going to go outside the case of the modulator. Now feed through the negative lead (the lead next to the - minus markings) of the 100µF 16V electrolytic capacitor through the spare left hand plastic hole in the modulator so that it goes to the centre pin of the TV aerial output socket. Trim it to length and then solder it in place.

Thank you for the details! I luckily had a 100µF capacitor on hand and installed it right away.
Sadly my wife is blocking the TV right now. I'll try later...

redgatemodels wrote: ↑Tue Mar 12, 2024 9:04 am I see it's got the same 48K memory upgrade that my S2 has. Note the extra little green PCB that allows for OKI DRAM

Did it get delivered like that?
Also some ICs are in sockets and some aren't. Did it also came like that?

My wife told me to dump everything I hadn't touched within two years.
Now she is my ex wife

I just hooked the device to my TV.
My TV does not have a composite input anymore, that's why I'm using the same hardware setup I use for my retro consoles.

Composite -> Koryuu-> Component -> GBS Control -> VGA -> HDMI converter -> TV

The output seems to be garbage tho. Key presses however change the flicker pattern. Anyone knows if there what causes these kind of issues?

Paul wrote: ↑Tue Mar 12, 2024 1:10 pm My wife told me to dump everything I hadn't touched within two years.
Now she is my ex wife

Well I wouldn't go that far lol. She let's me do my stuff, but interfering her favorite show is usually not a good idea lol.

P.S.:
How long does it take so that my posts don't have to be approved by admins. I feel sorry for them having to go through all my posts lol.

I'm not Shure. Two or three posts.
Don't worry, I read them anyway
It just takes some time if I am at work.

In answer to the chips in sockets, your machine was sold as a 16K RAM model. The chips in sockets have been added later. It was normal for Sinclair to fit sockets for the extra chips needed for the 48K RAM option.

Does the border always turn white at every power on? Do this (power cycle waiting 30 seconds in between) at least five times. If yes, the Z80 and ROM are likely okay,

Press down on the ULA (IC1) to make sure all pins are making good contact with the socket (assuming it's in a socket).

If you press a key (other than a shift key) do you hear the key click from the speaker?

If that does not fix the problem and you don't get a key click sound, it's possible that you have a fault with the 4116 (or equivalent) DRAM chips (IC6 to IC13j or IC3 or IC4).

Mark

1024MAK wrote: ↑Tue Mar 12, 2024 1:40 pm Does the border always turn white at every power on? Do this (power cycle waiting 30 seconds in between) at least five times. If yes, the Z80 and ROM are likely okay,

Border stays white all the time

1024MAK wrote: ↑Tue Mar 12, 2024 1:40 pm Press down on the ULA (IC1) to make sure all pins are making good contact with the socket (assuming it's in a socket).

I removed the chip from its socket and put it back in and also pushed it down when the device was turned on.

1024MAK wrote: ↑Tue Mar 12, 2024 1:40 pm If you press a key (other than a shift key) do you hear the key click from the speaker?

Yes, I hear click.

1024MAK wrote: ↑Tue Mar 12, 2024 1:40 pm If that does not fix the problem and you don't get a key click sound, it's possible that you have a fault with the 4116 (or equivalent) DRAM chips (IC6 to IC13j or IC3 or IC4).

So one (or more) of the RAM chips are most likely broken?

If you hear the key click sounds and BASIC appears to be running (try SAVE "P" ), then it's more likely to be a ULA fault rather than a DRAM fault. But without a test/diagnostic ROM or another ULA to swap with, it's hard to be certain.

Mark