What you got there sour grapes?

Retro, Sinclair

Sinclair ZX Spectrum +2

ZX Spectrum +2

ZX Spectrum +2

So, who’s up for a challenge?

I spotted this very poorly Sinclair ZX Spectrum +2 for sale online, and I thought to myself, “Self. Take a risk, see if you can fix it.” – so I did…

A History Lesson

The Sinclair ZX Spectrum +2 was the first model released after Amstrad bought the Sinclair brand in 1986. It has 128K of ram, and a built-in tape deck.

The built-in menu gave the option of 128K Basic, a Tape Loader, a Calculator and 48K Basic. I’ve wanted one of these for a while, and, as I’ll explain later, I really needed that 48K Basic…

Menu Screen - Sinclair ZX Spectrum +2
Menu Screen

So what’s wrong with it?

As I previously mentioned, this particular Sinclair ZX Spectrum +2 was quite poorly. I did approximately 15 seconds of Googling to decide if I could possibly fix it, before hitting buy – before anyone else did!

It arrived a couple of days later, and this is what greeted me when I plugged it in:

Corrupt Image - Sinclair ZX Spectrum +2
ZX Spectrum +2 Corrupt Image

Okay. I was expecting that. But could I really fix it?

My extensive Googling told me that the first thing to look at would be the RAM chips.

Now, the Sinclair ZX Spectrum +2 uses type 4464 RAM chips, and I had some similar chips from some Atari spares. My first method of trying to identify any dead ram chips would be to “piggy-back” the Atari RAM on top of the chips in the Spectrum.

This essentially involves putting a new chip on top of an existing chip on the board, and seeing if there are any graphical differences on the screen. Not very scientific, and I didn’t really get anywhere with this.

What’s the Diagnosis?

Well I’m glad you asked, using that specific phrase. I found a Diagnostic Test ROM chip on the excellent Retroleum website. For a mere £2.95, I might actually find out what’s going on. So I promptly ordered this, plus some ram chips, sockets, capacitor kit, tape belts, power switch, the works.

A few days later, everything arrived. I quickly plugged in the test ROM into the poorly Sinclair ZX Spectrum +2, and this is what greeted me:

Ram Fail - Sinclair ZX Spectrum +2
RAM Fail

Erm. What? ALL of it? That can’t be right can it. There are 16 RAM chips, help me out here!!!

Now, working in IT has it’s advantages. Using nearly 30 years of expertise, I turned the Sinclair ZX Spectrum +2 off and on again:

Useful Ram Fail - Sinclair ZX Spectrum +2
A useful RAM fail message!

So. Chips 12 and 6 were dead. Right? Wrong. Here’s the thing, and this will hopefully help anyone else encountering this, pay attention to the Diagnostic Test ROM documentation! This took me a while to suss out.

Firstly, it’s not 12 and 6. It’s 1, 2 and 6. But it’s still not that simple – look:

RAM chips - Sinclair ZX Spectrum +2
RAM chips

So first of all, they’re numbered 17 to 32. So where is 1? Is it IC32? Is it IC17?

The answer is neither. The Diagnostic Test ROM, checks contended RAM first. This happens to be ICs 25-32. 32 is actually 0. So the first failed chip is actually IC31. I replaced IC30 and IC26 too:

RAM Identification - Sinclair ZX Spectrum +2
ZX Spectrum +2 RAM Reference

Unashamedly pinched from here: http://www.retroleum.co.uk/diagrom/diagrom.pdf

Starting The Repair

Time to break out the soldering iron, and on a whim, solder wick. I’ve never used solder wick before, and always struggled with a solder sucker.

What a revelation! I will now desolder the entire Universe! The stuff is just magic. Put it over the solder you want to remove, heat it with the soldering iron, and watch it absorb all the solder. Incredible!

This Sinclair ZX Spectrum +2 will live!

And voila! One removed faulty RAM chip:

Removed RAM - Sinclair ZX Spectrum +2
Removed RAM

I put a socket in there so I can swap RAM chips in and out a lot easier:

Chip Socket - Sinclair ZX Spectrum +2
Socket to me!

Testing Times

Okay, let’s see if I’ve brought the Sinclair ZX Spectrum +2 back to life. First, the RAM test:

RAM Test - Sinclair ZX Spectrum +2
Success!

Tadah! It passed the RAM tests. Time to remove the Diagnostic ROM, put the original ROM back in and see what happens:

Menu Screen - Sinclair ZX Spectrum +2
Menu Screen

Yeeeeha! Yes, that is the same picture as earlier on in this blog, but it was taken after the faulty RAM replacement.

I tested the various menu options out, and loaded a game from my TZXDuino :

Knight Tyme - Sinclair ZX Spectrum +2
Time for Knight Tyme

Not Quite

Well that game didn’t actually load, and neither did any other 128K games. 48K games were fine. After a few attempts, I turned the Sinclair ZX Spectrum +2 off and back on again, and was greeted with a screen of garbage again.

So I set about replacing a few more RAM chips until the whole thing seemed a lot more stable. And 128K games were loading fine.

Disaster!

At this point I replaced the old voltage regulator and heat sink with a nice Traco switching regulator, took the keyboard apart and cleaned it all up, replaced all the capacitors and replaced the belts in the tape deck, so I could test that out properly.

Tape Deck - Sinclair ZX Spectrum +2
Below Decks!

After this, I put it all back together and it all seemed fine. Until I tried to select anything other than Tape Loader from the menu!

The trusty (almost unbreakable, so I’ve read) Sinclair ZX Spectrum +2 keyboard wasn’t working properly. In fact, Caps Shift, Z, X, C, V and the arrow keys had all stopped working! Aaargh! It worked before I cleaned the keyboard!

I spent days and days trying to sort this out. I cleaned the keyboard membrane a million times, I analysed every part of the membrane, I poured over diagrams of keyboard connections – none of it made sense. It *should* work!

It was at this point, I broke out the trusty multimeter and attempted to do some continuity testing. I didn’t really have a clue, but I vaguely knew which keyboard connection wasn’t working (for whatever reason), so I started there.

Then I spotted this:

Broken Trace - Sinclair ZX Spectrum +2
Broken Trace

Bingo! A broken trace, which, erm, traced all the way back to the keyboard connector! I must have scraped across this track when trying to remove a RAM chip – what an idiot.

I bridged the track and the keyboard sprang into life again. PHEW!

Side Quest

When I was 11, I lived in a block of flats. I was on the 8th floor. I had a ZX81. My friend lived on the 6th floor, she had a Sinclair Spectrum. Suffice to say I would go round hers a lot to play on the Spectrum – colour and sound!

We used to play this one particular game, and one day we completed it.

Fast forward a lot (seriously a lot of years) and all I could remember about the game was a treasure room. Or at least, I though it was. I couldn’t remember what the game was called, or any other detail about it. It’s been bugging me for years.

While repairing the Sinclair ZX Spectrum +2, I knew I needed to test the tape deck out. So I started looking for some cheap tapes I could pick up online. Suddenly, there it was! The picture of the treasure room, not quite as I remembered it, but undoubtedly, this was it!

Treasure! - Sinclair ZX Spectrum +2
I guess my imagination was better back then!

Actually, just adding that image above has triggered another memory. That screen didn’t just appear, I think it must have drawn it – very slowly…

Anyway, the game is called Transylvanian Towers, and I knew I had to get a copy and play it – however awful it turned out to be.

Transylvanian Towers - Sinclair ZX Spectrum +2
Transylvanian Tower

This had to be loaded from 48K Basic, hence how I found out the keyboard had stopped working.

Summary

So this particular Sinclair ZX Spectrum +2 has lived to see another day. I’m so pleased on so many levels. I’ve rescued an old piece of tech, I’ve discovered solder wick, I’ve managed to remove chips from a motherboard without completely destroying it! I’ve done a lot of fault-finding, and I finally found what that game was called. I definitely levelled-up my skills on this one.

Next up, I need to either make my own, or purchase a joystick adapter. Why? Well, guess which particular Sinclair ZX Spectrum +2 uses its own proprietary joystick format instead of the usual ones? Yup. The fun never ends!

By the way, the tape deck works!

Blizzard Pass - Sinclair ZX Spectrum +2
Blizzard Pass
Transylvanian Tower - Sinclair ZX Spectrum +2
Transylvanian Tower
Count Kreepie! - Sinclair ZX Spectrum +2
Count Kreepie!
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