ZX Spectrum+

After the well known ‘rubber keyed’ Spectrum came the ZX Spectrum+.  I never encountered one during my childhood, probably because they came out a little later, but also because I was perfectly happy with my 48K.  The Spectrum+ is basically a 48K with a ‘proper’ keyboard – nothing wrong with the ‘rubber keys’ ;). Either way I wanted one for my collection, so off to Ebay again, and it wasn’t long before a boxed Spectrum+ was sitting on my bench.

ZX Spectrum+ (Issue 6A)

First impressions were that it was in good condition, but very dirty.  Voltages checked out fine, a good sign, but no picture when I plugged it into my TV.  I decided to perform the standard composite upgrade first given my success with this is in past.  And guess what ?  It worked – another dodgy tv out circuit.

Well that was easy.  Now for the standard future proofing, recapping and replacement of the linear power regulator with a switched regulator.

Recapped and new power regulator

As a final upgrade I fixed a heat-sink to the ULA to improve its chances of working for a few more years.  Pleased with that – fully working mint Spectrum+ Issue 6A from 1984.  The only thing left was a good clean, especially of the keyboard.

I knew it was all going too well – on reinstalling, the keyboard membrane completely failed 🙁 Luckily, as with most Spectrum parts, a new membrane was easily sourced on the internet.

Time for some proper testing.

Proper testing

It was now ready to join my others on the Spectrum shelf …

Job complete.

My First ZX 81

I started my computing with a ZX Spectrum 48k.  I never really noticed the ZX80/81 and I don’t remember any of my friends having one.  But they both played a significant part in kick-starting home computing.  For this reason they were next on my hit-list for acquiring, off to eBay.  As with the ZX Spectrums the prices vary significantly, especially if they are known to be working.  What I hadn’t realised was the price ZX80’s are going for.  I decided to set my sights on getting a ZX81 first.

It didn’t take long to win two auctions, the first for a ZX81 console, the second for a 16k RAM pack; I remember these being legendary for falling out and resetting the console.  

I started with opening it up and doing a visual check, the immediate issue was the keyboard.  Something had obviously happened to it with ‘ripples’ all the way around and one corner peeling up.  On opening it up I also found that the membrane connection to the motherboard was also snapped.  There was no saving this keyboard, luckily new ones are available for £10.

The voltage checks and it all looked good so I decided to try powering it up.  I plugged it into my analog tv and turned it on.  The boot ‘K‘ was sort-of displayed, although the TV was obviously having issues tuning the channel; but the good news was that it was working. 

I decided to start the future-proofing while waiting for the new keyboard to be delivered.

The changes were to replace the 5v regulator with a switched regulator to reduce the output heat, replace all the capacitors and to add a heatsink to the ULA.  The keyboard was fairly easy to remove with the help of a heat-gun.

Initial strip down
ZX 81 motherboard

The final mod was to upgrade the video to output a composite signal.  This is slightly more involved that the Spectrum requiring a transistor and a few resistors.  I created a prototype board to check the circuit, unfortunately I didn’t have any 33 Ohm resistors to used 3*10 Ohm in series for the prototype.

The results were a little bright, this is due to the lower value resistors being used.  I decided to order the correct values and do a more professional job when they arrive.  

I also replaced the keyboard, another 2 minute job, but it looks great and all the keys passed my first test.

Fully refurbished

Job complete.