Entries in this series:
- 1) TS1000 upgrade
- 2) More Power!
- 3) On The Big Screen! « you are here
- 4) Oh the memories we’ll make with 16k!
2023, 02 , 24
If you’ve been following along, you may recollect that this journey to modernizing my vintage Timex Sinclair began when I watched this four-part video series by The Byte Attic, and decided ‘yeah, that looks like something I could do’. If you’re jumping in at this point, well, I’ve done things and have more things to do. This post will look at converting the video output of the computer from an RF signal to a more modern composite video signal with a simple hardware modification.
First, a bit of background information:
RF (Radio Frequency) signal:
RF signal is an analog modulation technique that encodes video and audio signals onto a carrier wave, which is then broadcast over the air. RF signals are typically transmitted over coaxial cables or through the air, and are received by a TV tuner or other receiver.
Over the air. That’s back in the days when you received your TV through things called rabbit ears (antenna) that were on the back of your TV. Or maybe you had a nice flesh-coloured coax cable coming into various rooms in your house. Vintage.
The RF Modulator is a box that sits inside the computer and puts out the RF signal. That’s what we’re going to be working on so that it’ll put out a composite signal that our TVs and monitors can understand today.
There are a few different ways of managing this modification. I selected an all-in-one approach purchased from eBay. This PCB modification works for the original ZX81, Timex Sinclair 1000 and the Timex Sinclair 1500.
In the spirit of keeping my modifications reversible, I opted to not remove the existing RF components as the board was small enough to fit in with them still in place. The modification uses the existing RCA-style jack to send the composite video signal to the monitor.
Following the designer’s helpful and detailed instructions, I was able to cut and solder in the wires at the appropriate places. Because the installation area is crowded with the existing components, I used wire harvested from a standard Cat5 network cable. The wire is thin, somewhat rigid, and works well in the confined spaces. The stiffness of the wire will help keep the board from moving around within the aluminum box.
Speaking of the aluminum box, I was having no luck soldering the ground lead from the PCB to an inside wall of the RF Modulator box. I’d scored it, sanded it, cleaned it, but the solder wasn’t really adhering to it in a way I was happy with.
So I got out a pin-vise drill and drilled a small hole in the box, routed the ground lead through that and then soldered it to the outside of the box (after I’d cleaned and scored the outside wall). The solder seemed to stick better so I moved on to the other wires.
Once I finished the soldering, I put some simple insulation (a thick piece of paper) below and above the composite video mod board before closing the RF Modulator case back up. This should help prevent any issues with the components on the mod touching any original legacy components.
Magic Smoke Test?
To test, I connect a video cable between the computer and the TV. I used my bench power supply to power the computer — yes, I had the original power supply from the computer but I wanted to hook up some wires and have some LEDs on the power supply glowing in the background as I tested this thing, you know, like a real electrical engineer would do 😀
And it worked! A nice, clean, stable signal that the modern TV would display.
All told, it took maybe a couple of hours to do this from start to finish. I maybe took a bit longer as I reviewed each step a few times, taking time to ‘exactly’ locate each solder position within the modulator box.
Well, the stock TS-1000 is somewhat capable out of the box. It has 2k of RAM though, so that’s a bit of a limit. I do have the external 16k RAM expansion box that mounts to the edge connector on the rear of the unit, but as I discussed in my first post, the goal is to improve the little computer. So next will be adding in a reversible internal 16k RAM modification.
It’ll be a bit trickier than this video modification — more lines to solder and more potential for things to go wrong. I’m looking forward to it!
- Working in tight, confined spaces meant more time was needed figuring out how to route the wires and where the soldering iron would approach each solder point etc.
- Minor mishap while fitting the PCB in the box. Managed to partially dislodge diode D2, but a quick solder/adjust put it right.
- This modification looks more intimidating than it actually is. Afterward, I felt that I was a bit too apprehensive before going into the work.
- Looking for alternative placement and routing is a good thing. It forces you to review the schematics and check your wiring. I’m kinda pleased with my solution to my ground-wire issue.
- Glad I found a somewhat local supplier of this modification board. Same country anyway 🙂