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Making a good Spectrum +2A from two duff ones

I've had two black Spectrum +2As boxed up for many years. I think both may have been car boot sale finds at a time when I was using a grey +2. One has never worked properly, one did. I used it a bit, had it repaired at some point (it has the repairer's sticky label on the bottom, I remember taking it there, but I don't remember what the fault was or what he did.)

When I plugged them both in recently, the latter one worked for a little while but then developed vertical stripes.

I've written a separate post about checking out and working on the power supplies.

As one of the cases was mint, and the other broken, I decided to take the best from both and hopefully end up with at least one working board in the good case. (and possibly a second working board, or at least spare components.)

One board already had the memory chips socketed. The other had them soldered directly to the board, and I think these were the suspect set, but the best-working board generally. I desoldere…
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Repairing two black Spectrum +2A power supplies

I've had a project going to make a perfectly-working and perfect-looking Spectrum +2 from two non-working ones.

One (a car boot find from many years ago) has never worked, the other I bought and used quite a bit in the 90s. When switching it on again recently it ran fine for a little while and then vertical stripes appeared.

I'll write separately about getting a working board from these two and putting it in the best case of the two.

Because of that new vertical stripe problem, I checked out both PSUs, which have +5v, +12V and -12V. (Though the -12V is only used for the serial out I think). Both measured fine except for the -12V.

On delving deeper I found some disturbing things. In both cases it appeared that this fuse had blown. It turns out that although this one looked blown at first glance, someone has soldered wire across it. I don't know whether this is fusewire of the appropriate rating.

That's connected to a low-resistance, high wattage resistor. In both cases …

Updating an Amiga power supply

This is the finished project. As well as being the size and shape of a house brick, it used to be the same weight as one too. It ran hot, and it's risky to depend on a supply that's decades old.

I'm sure that the credit goes to Neil at Retro Man Cave. I'm pretty sure I saw this upgrade in one of his videos and then discussed it with him, although I can't find the exact video now. Ms Mad Lemon has also done the same thing, so credit to her too.

I have three Amiga PSUs and they're all different shapes and sizes. This is my largest one, and it's the one that is the right size for the Mean Well power supply which is recommended for this project. Further below is a shot showing the part number. It happens to have +5v, -12v and +12v out ,which is exactly what the Amiga needs. It also fits this case snugly. Almost as if it were designed for this job!

I bought the new supply a year ago, but couldn't get into that plastic case. The screws are a long way down a …

Making more music using Commodore 64

This weekend I've tried a different approach to writing and recording a song and it's worked out so well I thought I'd make some notes here about the process.

First of all, here's the finished music. I only spent an hour or two actually writing it. That was in itself an exercise in composing but I wanted to try this new method of recording and just got something down to work with. I like it a lot and will definitely expand it.
All sounds here are produced by the C64, albeit one fitted with an ARMSID (set to 6581). Only because my working C64 with a real SID chip is playing up.

Rather than try to write for 3 or 6 voices and then import that information to end up with a .prg that will run and play the music (aka a "sid") I've written any number of parts, with up to 3 voices in each, and used the C64 as a MIDI instrument, sending each part as MIDI to the computer and recording the audio that comes out of the computer.

I think that Logic and other DAWs allow …

Word Processing like it's 1984 : Commodore Plus 4 Restoration

I'm typing this blog post on the Plus/4 itself.

I'll have to transfer to something more up-to-date before posting because Commodore didn't include a web browser alongside the word-processing, spreadsheet, graphics and database packages that they built into this machine.

The first word-processor and spreadsheet I used were on the Amiga. When I saw that the Plus/4 had even earlier examples of such packages on-board, I was curious. There was a non-working one in my collection, bought sometime in the 90s at a car boot sale.

The 1984 Plus/4 has a lot in common with the Commodore 16. In fact they share the same key chips.
The Plus/4 just has additional RAM and the office software on ROM. On opening up a 'spare' working C16 and the Plus/4, I found the important chips socketed and identical, down to revision numbers. Chip-puller came into play and chips were exchanged one at a time, starting with the most likely suspects until the Plus/4 worked. In this case the TED and P…

Home-made real keyboard for ZX81

A ZX81's keyboard is frustrating to use. Especially for games. One too many times, you find your finger isn't quite over the pad when you have to make that crucial jump...

It's easy to use an emulator, but personally I don't get the same buzz.

My first computer, probably in '82 was a secondhand ZX81 which had been screwed to a board along with some kind of aftermarket keyboard (which really wasn't very good).

So for that reason I feel perfectly OK about sorting myself out with something similar now.

After looking at many options (including the ZX-Key, which looks excellent and the Minstrel keyboard which has tactile switches) I noticed while recapping a Spectrum +2 that the keyboard connections are very similar to the 81's:
There are more lines because the later spectrums have many more keys. But some study of the matrix diagrams made me think that they were compatible* if you take the first five and the first eight lines from those ribbons.

I *really* like…

Getting a great display from a ZX81

The ZX81 was my first computer. Mine was screwed to a board with a terrible external keyboard, and I was proud of the fact that someone had fitted 2k of RAM.

It was my introduction to BASIC and machine language. Let's not forget that the humble zeddy is a vehicle for a Z80 (which has 16-bit features) running at >3Mz. (Of course you can only harness that amazing power in fast mode, ie without display output, because much of the CPU time is usually used to generate the display.)

Other than buying some kind of box that will convert the TV signal (with which I had limited success), it's possible to perform surgery to convert the output to composite, which modern displays may be more likely to display (but still maybe not in the case of the ZX81s with the older ULA).

Here are three methods - rewiring (cost zero), using some simple components (cost pence) and a purchased modification (still less than a tenner.)

With the newer issue 81 it's possible to simply tap the signal be…