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

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.

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!

Notes:

• 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 🙂