Sinclair ZX80 / ZX81 / Z88 Forums

Hi all

How do you get a composite image out of a toastrack? I believe one pin in the RGB socket carries the signal? Assuming so does anyone know where I can get a suitable cable (ideally one which carries sound)?

Making them is not my speciality...

Thanks!

Are you up for soldering an insulated wire from a resistor lead to the centre pin of the phono connector in the modulator (after disconnecting the resistor and the input and +5V supply wires)?

Or do you wish to maintain the RF UHF output?

Mark

1024MAK wrote: ↑Sun Jan 03, 2021 8:33 pm Are you up for soldering an insulated wire from a resistor lead to the centre pin of the phono connector in the modulator (after disconnecting the resistor and the input and +5V supply wires)?

Or do you wish to maintain the RF UHF output?

Mark

No problems with losing RF to get composite thanks.

Tomorrow then

As I’m about to watch Magnum P.I.

Mark

1024MAK wrote: ↑Sun Jan 03, 2021 9:57 pm Tomorrow then

As I’m about to watch Magnum P.I.

Mark

Nice!

The reboot?

I have done the RGB mod shown here: https://spectrumforeveryone.com/technic ... compliant/ (replacing R134 etc.) so I may need to do a little roll back first?

ZX Spectrum 128k Toastrack Composite Video Modification to the Modulator

Composite video is available on the monitor/RGB socket:
Pin 1 = composite video
Pin 2 = 0V/GND/ground/screen

To replace the RF UHF TV signal from the modulator with a composite video signal, follow these steps:

• Disconnect the existing +5V feed wire and the video signal wire for the modulator from the PCB. Either by heating up each of the solder joints until the solder becomes molten, then very gently pulling each of the wires out of the PCB with small long nose pliers. Or you can just cut both wires close to the board. You can then bend them up from the PCB, out of the way.
• Inside the modulator, disconnect the existing resistor that connects to the centre pin of the phono/RCA/Cinch connector on the modulator case.
• Locate resistor R134 (75Ω) on the main board. Use a multimeter on the continuity range (or 200Ω resistance range) to find the lead that connects to pin 1 of the DIN socket.
• Now strip about 3 to 4mm of the insulation from an insulated wire, tin the wire, then solder this to the lead of resistor R134 (75Ω) that you identified in the above step.
• Route the wire through the spare hole in the modulator. Use the shortest route to keep the length as short as possible.
• Then solder the wire to the centre pin of the phono/RCA/Cinch connector on the modulator case.

You may want to stick a label on the rear or the underside to remind you that the former RF/UHF output is now a composite video output.

But Lardo being ‘special’, you have presumably removed R134?
So instead of soldering to one lead of it, you will need to do these steps:

• Disconnect the existing +5V feed wire and the video signal wire for the modulator from the PCB. Either by heating up each of the solder joints until the solder becomes molten, then very gently pulling each of the wires out of the PCB with small long nose pliers. Or you can just cut both wires close to the board. You can then bend them up from the PCB, out of the way.
• Write 500 lines saying “I’ll tell Mark everything I’ve done to my machine when I ask for help”.
• Inside the modulator, disconnect the existing resistor that connects to the centre pin of the phono/RCA/Cinch connector on the modulator case.
• Report yourself to the RSPCA (Respect Sinclair Personal Computers and Accessories) society.
• Locate where resistor R134 was on the main board. Use a multimeter on the continuity range (or 200Ω resistance range) to find the PCB pad/hole for the lead that connects to the emitter pin of transistor TR14 (ZTX313). Keep note of this PCB pad, we will come back to it later.
• Go through your trash can to find that poor 75Ω resistor, or buy a new one (a 250mW / ¼W type or a 500mW / ½W type will be fine).
• Thrash yourself with a branch from a holy tree for taking advice from another site about tinkering with your Sinclair machines.
• Get some black heat-shrink insulated sleeving of a suitable size that it will slide over the 75Ω resistor, plus some smaller diameter heat-shrink to go over the solder joints you will be making to its leads.
• Now strip and solder an insulated wire to one lead of your 75Ω resistor. Do the same for the other lead. Fit the heat-shrink sleeving to the joints and over the resistor.
• Route one of the wires from the 75Ω resistor through the spare hole in the modulator. Use the shortest route to keep the length as short as possible.
• Connect this wire to the centre pin of the phono/RCA/Cinch connector on the modulator case.
• Then solder the other wire from the 75Ω resistor to the former R134 PCB pad that you located earlier (that’s the one that connects to the emitter of TR14).
• Hand in your 500 lines.
• Check. Then double check that there are no possible sources of short circuits, power on and test

I hope that’s clear

Mark

Lardo Boffin wrote: ↑Sun Jan 03, 2021 10:10 pm The reboot?

Yes!

Mark

75Ω Resistors ordered.

Lines nearly done.

Resistors arrived. Lines complete. Reported self to RSPCA.

Working on the assumption that the emitter is on the left and subtly marked E it goes to the pad shown:


Which makes sense as the input to R134 now comes from the 12V carrying cap and goes down to blanking voltage level via the new R134, the other side of which goes directly into pin 1.

So from here on in I am just basically connecting the emitter output via a 75ohm resistor directly to the output of the modulator.

Yeah

Mark