Composite Output Mod

The TV output of a Speccy isn't brilliant at the best of times, so when the best that Speccy No2's output could manage turned out to be grey, rolling and noisy - rather than mess about, it was time for the composite mod.

I followed the tutorial on Sami Vehmaa's old site after looking at a few others, some use a 100µf 16v electrolytic capacitor between the signal input and the socket and quite a few others don't, so if you need your machine up and running post-haste then it seems safe to omit if you don't have one to hand, all I could find was a 10v one which seems to work OK.

I levered the top of the modulator off with a small flat-blade screwdriver, taking care not to totally mangle it and set it to one side. It's no longer really needed, other than to clip back in place when you've finished, making for a neater looking mod.

The unwitting victim

Once the PCB inside was exposed, I set about clipping the 5v, signal and output lines, I cropped the 5v line as close to the outside of the modulator as possible and as close to the Speccy's main board as I could too keep it out of harm's way, it can always be re-soldered through the board if it's needed again. Try and crop the signal line as close as you can to the modulator's board, otherwise you'll run into problems later (like I did) when you come to soldering the capacitor into place.

I managed to shatter at least one of the ceramic capacitors inside the modulator when I clipped the signal line, despite still having cut it way too close to the inside of the case, so I decided that I might as well remove the whole lot. What followed next was sheer butchery and I recommend that anyone else doing this take much more care than I did. The piece of shielding that holds the modulator board in place is spot welded to the rest of the modulator and had to go, much twisting and pulling later it finally snapped off. I then flattened down the tabs retaining the board from the sides, leaving me free to lever it out with a screwdriver in three pieces :-/.

The modulator denuded of it's PCB

Now for the fun part, I plugged my soldering iron in and started searching for a 100µf 16v electrolytic capacitor - of course, I could only find was a 10v one, so I won't replace the modulator's lid until I've replaced it with a 16v one, I don't want it to suddenly go BANG! in a shower of sparks when I least expect it. The only real problem I had was the length of the signal line where I'd cropped it, so instead of soldering it to the capacitor inside the modulator, I pulled the signal line out and pushed the leg of the capacitor through the hole in the side of the modulator, soldering it to the signal line outside.

Make sure you solder the capacitor with the correct polarity, the negative side (with the stripe) going to the socket pin and the positive terminal to the signal line. Like I said earlier, some versions of this mod omit the capacitor completely so the likelihood of my 10v capacitor letting go seems to be fairly minimal, even so I'll replace it with a 16v one as soon as I can.

100µf Capacitor soldered in place.

Just a quick double check to make sure there were no bits of modulator or solder waiting to cause a short and we were ready for testing. I grabbed my SCART breakout lead that I paid £4 for some 18 years ago back in my Amiga days and connected everything up, unsure whether to cross my fingers or stick them in my ears. I connected the PSU and hey-presto, there it was - no distortion or noise and only the minimum of ghosting, the clearest and sharpest '1982 Sinclair Research' I've ever seen outside of an emulator.

Hallelujah!

It's worth noting that the horizontal bars aren't visible in reality, they're caused by the camera capturing images much faster than the TV's refresh rate which is always a problem when photographing CRT screens, although the familiar 'moire' pattern is still present.

Expect to pay about £5+vat and p&p for a pack of 100 capacitors from somewhere like Technobots but unless you're doing this to a lot of Speccy's then £0.99inc p&p for a pack of 10 capacitors from Ebay isn't too bad, this is one instance however that Maplin's prices aren't actually eye-watering if you're in a rush (£1.04 for four resistors anyone?) and at £0.20ea their 'Fine Gold' capacitors are for some reason even cheaper than the standard ones at the time of writing.

Enough Maplin bashing for now I suppose, but the time was when they were geared toward the hobbyist & enthusiast, not selling cheap Chinese computer stuff, tools and gadgets at vastly inflated prices.

I want to keep at least one other Speccy boxed and as original as possible, the question is do I perform this mod on it to make it usable on a modern TV or leave it as it is?. It was hard work tuning it in and getting a signal on an old non-digital CRT TV and I can't see it being any easier if I were to connect it to the RF input on my 42" LCD, not to mention the fact that TV's with an analogue tuner can only become rarer now that analogue terrestrial TV is no more in the UK.

All I need now is a working keyboard...