TS1000 upgrade – log entry 3 — On The Big Screen!

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.

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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.

What’s next?

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 🙂



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4 responses to “TS1000 upgrade – log entry 3 — On The Big Screen!”

  1. Dave Farquhar Avatar

    This was a fun series to read. I’m glad to see your TS1000 lives. It exis­ted dur­ing a very excit­ing time in home com­put­ing, and even after Timex dis­con­tin­ued it, the remain­ing stock lived on as the Rasp­berry Pi of its day, an inex­pens­ive com­puter for tinkerers.

    1. brad Avatar

      Hi Dave, thanks for the kind words! Agreed with you on the excite­ment of the time. I worked retail in ste­reo shops and com­puter stores at the time and there was a lot going on!

      Funny thing is, in some ways the time we’re in now is even bet­ter if you’re into vin­tage com­puters like these. We have instant access to vast know­ledge about these through sites like Archive.org. We can search on any top­ic and get poin­ted in the right dir­ec­tion. And there are many pods of inter­ested enthu­si­asts instantly able to com­mu­nic­ate. Amaz­ing times we live it. Heck, we live in the Future! 😀

  2. Rambounce Avatar

    I got back in to basic pro­gram­ming and vin­tage com­put­ing through the TS1000. My dad had one when I was not quite yet thought of. I unsuc­cess­fully installed a com­pos­ite video board much like this one and your blog will be very help­ful in troubleshoot­ing my work. Thanks for that! 

    In the mean­time, I grabbed a mod­ded (com­pos­ite video, 16k on-board, improved tact­ile mem­brane, zx-wespi load­er) zx81 off that dreaded auc­tion site to get my fix for the time being. Sinclairzxworld.com is your best friend and user Lardo_Boffin is par­tic­u­larly know­ledge­able and help­ful. Best of luck!

    1. brad Avatar

      There are so many inter­est­ing options out there on the auc­tion and retro sites. I find it hard to stay focused. I’m in it for the learn­ing — I’m not an elec­tron­ics engin­eer by trade, just play one in my work­shop from time to time, and have a few unsuc­cess­ful pro­jects on the shelf. I like to think of them as ‘learn­ing exper­i­ences’ 🙂 even if I’ve not solved the issue yet.

      ZX-Wespi is in this unit’s future. I like the idea of not hav­ing to fuss with tape — did that for too many years. Though part of me remem­bers the accom­plished sat­is­fac­tion of finally get­ting a pro­gram to load! I’ll take the quick load­ing of the Wespi now.

      Thanks for point­ing out those resources. I’d not seen them before so am check­ing them out this morn­ing! Luck with your retro future too!

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