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Speccy, Vol 8: The 128k

March 5th, 2016

If you've been reading these blog posts you may remember that I ordered a 128k speccy (a grey +2 to be precise) off eBay long ago. It arrived, was very well packaged and was in precisely the shape it was advertised to be in, i.e, no idea whether it works or not, but has worked sometime in the past.

Luckily, unlike some later models, it uses the same power as the 48k I have - no way I was going to use the original monster of a power brick. I powered it up.

And I didn't get a picture.

I figured that I've got this, popped the thing open, and did the same video out modification as I had with the 48k... and got no picture.

In addition to the old style composite TV plug the 128k also has something called "RGB" output, which I believe is a rather custom plug. I found the wiring for said port and a couple pins in it also has the same composite TV out signal, so I tried plugging some wires into those holes and held them to the video cable, and got an image.. completely out of sync, black and white, and what appeared to be corrupted characters in random places.

Disheartened, at this point I was ready to just sign the thing as DOA, put it on the shelf, but did a post on the world of spectrum (WOS) forums. And got a bunch of replies, explaining what might be wrong... and there sure are a lot of things that are wrong with the specific make and model of speccy that I had bought.

Among these things is the fact that the motherboard has transistors that are installed the wrong way around. At the factory. Yes. I have no idea how these things have ever worked.

Anyway, I had done enough soldering for some time at that point and concentrated on other things for a few months.

Fast forward to today. This weekend I was ill with some kind of flu, my wife was on a trip so I had to look after our son, and I had a small soldering project of fixing my wife's broken headphones, so, since I already had the tools out and was already feeling miserable, I thought what the heck, let's give it a go.

In the meantime someone on WOS had posted photos of a simple mod they had done to get the video signal working, so I figured I might as well try it. What I got as a result was the out of sync image - without corruption this time - directly out of the composite TV connector. So, progress.

Posting about my progress on WOS again I was pointed at some resources which told me that I'd only need to fix one of the transistors. I spent an hour or so trying to desolder one before giving up. I'll be the first to admit that I'm not good at desoldering. The transistor is a tiny little thing in a crowded place on the board so I couldn't just grab it with my fingers, and pulling with pliers wasn't working and I have no idea where my desoldering pump has got to, probably lent it to someone who never returned it.

Eventually I just cut off the transistor's legs, soldered short wires to the board and the remaining stubs of wires on the transistor. The result is REALLY ugly, but it did the job, and I got stable image out of the machine.

The next problem (which I had already posted about on WOS earlier and got discussion going) was getting data onto the machine. The thing is, the original speccy depended on external tape player, but the 128k one has an internal tape deck ("datacorder"). With the integrated tape thingy, they didn't think anyone would want to use an external audio source, so there's no plug for it.

I believe some later model may have that by default, but this one didn't. There's a relatively simple modification that can be done though, making the device think that the audio is coming from the "datacorder"; I did this and (after a couple of false starts) got it working. When loading data to the 48k I have to boost volume rather high for it to work; the 128k loads at reasonable volumes. I believe this is because the audio goes through the "datacorder's" amplifier.

So now I have a (relatively) working 128k +2. The audio output is crazy noisy, there's still a couple of transistors that are the wrong way around (but don't affect my use apparently). I'm pretty sure there are other issues too, but it's in much better shape than it was yesterday. Now, if I'd just get over this flu..

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