Skip to main content

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 desoldered those chips and put in sockets.


I've ordered more 'new old stock' ram chips, but they've taken an age  to arrive and I didn't need them anyway, one of the sets of ram chips worked perfectly.

I recapped both boards, which I now believe in doing as a matter of course.

Surprisingly it took very little work to put together a working board.


After a scrub, the good case looks fantastic. I didn't mess with its keyboard or tape mechanism as all seems fine with those.

This is a ram test, which I left running for a long time and it showed that everything is fine.


The final job was this audio mod. Loading programs and games from my ZXDUINO into +2's and +2As does work if I use one of those car tape converters (as you can see above) but it is a little flaky. (Or perhaps my adaptor isn't very good quality. Either way it all feels a bit makeshift and doesn't work every time.)

You have to cut one track and add one wire.



After that, with the right lead you can plug the spectrum into a powered speaker and a ZXDUINO at the same time, and both work perfectly.


Comments

Popular posts from this blog

Driving NeoPixels with Z80

I 've long been thinking about a version two   RC2014 LED matrix module . I've had a matrix with a MAX 7219 on a module. It's a nice enhancement. But there's only so much you can do with a single-colour LED array right? Wouldn't it be cool to have RGB LEDs?  At Liverpool MakeFest I saw a wall-sized ping-pong ball NeoPixel display and picked up some NeoPixels with the intention of making one. Possibly driven by my RC2014.  I enjoy learning about protocols and have had some SPI devices working with the RC2014 - bit-banging SPI works really well because it doesn't care about timing. NeoPixels really do care about timing though. From Adafruit's web page about their 8x8  NeoPixel matrix: If there's one thing I want to get across in this blog post, it's don't just accept what you're told . Question everything. Learn about what's going on and find out why you're being told something isn't possible. Get creative with workarounds. I'

ZX81 reversible internal 16k upgrade

T his post is an upvote for Tynemouth Software's  ZX81 reversible Internal 16K RAM upgrade . Their instructions are easy enough for even me to follow and don't involve cutting tracks. This is the ZX81 I've had out on display and used whenever I wanted to. It's an issue 1 and was probably a kit judging by some very untidy assembly. It has a ZX8-CCB  composite video mod and an external keyboard fitted. On board it has two 1k x 4-bit chips.  The ZX81 originally came with 1k on board. Thanks to a trick with compressing the display in ram, that was enough to type and run a small program but you soon felt the limitations. Back in the early 80s, the solution was a 16k ram pack which plugged into the back[1] and this is the way I've been using this particular machine. These ram packs are notorious for 'ram pack wobble'. Even if fastened into place, you can still randomly find your work disappearing. This is a very reliable solution using a more modern 32k chip (half

Making new ROMs for the Vic20 / Vicky Twenty

M y Vicky Twenty is very nearly complete.  As things stand, the board and every single component is new*. The processor and VIAs are newly-manufactured (W65C02 and W65C22).  Obviously the Vic1 chip isn't manufactured today, but there is 'new old' stock about. I have been able to buy a Vic 1, date code 1987 (which seems very late). It obviously hasn't been in a computer before, passes the acetone test and works. The same goes for two of the ROMs - character and BASIC. But I haven't been able to buy a new-old Kernal ROM (901486-07). I am able to borrow one - all of the boards I have, have this particular ROM socketed. I don't know whether all of this indicates that the Kernal has proved less reliable than the other two. I recently bought a TL866 for another project. Of all the retro-computing hardware things I've had to learn to do, making ROMs has been one of the simplest. So far, everything has been very easy and worked first time.  I'm not sure that it&