EEVblog #557 - Retro Sinclair ZX Spectrum Computer Teardown

[EEVblog]

Inside the classic retro Sinclair ZX Spectrum computer from the 1980's
Was supposed to be part of the previous Mailbag video, but Dave is an SEO keyword whore, so it gets it's own video.

[lilshawn]

I had the "TIMEX" branded Sinclair ZX81 with the horrible to type on membrane keyboard...none of that fancy silicone you got there... had the 16k expansion pack too. (i believe it was only $99 with the pack where the straight sinclair was 130...something like that.)  cut my teeth with basic on that puppy! saved 'em on audio tape too!... good times, good times!

EDIT: oops! 16k not 64k - could you imagine!?!? 64k? BWAH!

[ttp]

Had one of them and remember RAM chips going bad quite often, at some stage installed sockets for RAM to streamline the repairs.

[kayvee]

I skipped the Spectrum and splashed out the extra cash on a BBC Micro Model B, at least it had a proper keyboard, and a 6502 processor!

Exciting times it was, even though we laugh at them today

[davec]

I love these old computers, so when I get one like that which is not going to work again, I convert them to USB keyboards. I've done many of these, details on my blog. I initially used ATMega328P microcontrollers (ala Arduino UNO), then moved onto Arduino Lenoardos
http://blog.tynemouthsoftware.co.uk/2013/05/zx-spectrum-usb-keyboard.html


Lately, I've designed a PCB for this for some of the larger keyboards (such as the Commodore 64), which is basically an ATmegs32U4 breakout board.
http://blog.tynemouthsoftware.co.uk/2013/12/usb-keyboard-pcbs.html


There is also just about enough space to stick a Raspberry Pi in there as well, if you're that way inclined.

http://blog.tynemouthsoftware.co.uk/2013/11/zx-spectrum-raspberry-pi-case-mode-usb.html

I can stick a PCB in the post to the EEVBlog lab if you're interested in converting that spectrum.

I also have some for sale on Etsy, if you don't want to do it yourself.
https://www.etsy.com/uk/shop/TynemouthSoftware

Thanks,
Dave

[Rasz]

Had one of them and remember RAM chips going bad quite often, at some stage installed sockets for RAM to streamline the repairs.

I remember hearing somewhere DC/DC converter in ZX Spectrum was a freak of nature and that it killed ram chips with fluctuating -5V rail (or something, it was so long ago)

[davec]

The DRAM was always an issue, the 8x2K 4116's in the lower 16K needed 12V and -5V, and those rails going tended to go and take the chips with them. The inductors also buzz quite loudly these days.

The upper 32K was actually 64K, 8x8K 4164 chips which were only half bad. They would be binned so the faults were all in one half or the other and jumpers on the board select which half to use.

Usually though, the Ferranti ULA's burn out long before the RAM goes bad.

The heatsink was missing on the board in Dave's video, it is normally a lump of aluminium bolted to the 7805, but they too get rather hot as they dissipate 5-10W sometimes.

Thanks,

Dave

[RetroSwim]

Imagine my face when I clicked video #557 and saw my parcel in the limelight! 

The system that got revived thanks to this poor fellow's demise is a Spectrum+. Same motherboard, but kitted out with a Sinclair QL style keyboard.

[Stonent]

I started on the old TRS-89 MC-10 which design wise was a lot like the Spectrum.  It had keys with the commands over them which you could make appear by pressing a Control key. It even had the graphics characters on they keyboard as well.

[firehopper]

my first computer was a ti-99-4a.
had a lot of different computers over the years.. I actually found a old trs-80 model 100. and it still works. I can post pictures if anyone wants.

[Terabyte2007]

Dave should try and get his hands on an early Commodore 64 computer. If I can find one, I may try and send it to him. The Commodore 64 was my first computer, I remember writing code in BASIC and at first I did not even have a tape drive (Cassette Tape Storage), Yes!. I would have to retype my program each time I wanted to use it. I soon after acquired a cassette tape storage unit. Sitting on the floor in front of my TV with a RF adapter connected to the composite output, those were the days!  O0

[synapsis]

I started on a VIC-20. 3853 bytes of ram free!

I have a small shrine to Commodore in my living room.

[Kjelt]

I started on a VIC-20. 3853 bytes of ram free! 

That's still more then the embedded device with 2k I have to work with 

[Terabyte2007]

I started on a VIC-20. 3853 bytes of ram free!

I have a small shrine to Commodore in my living room.

Very Nice! Love your Commodore Shrine!

[carpelux]

It sure brings up lot of memories watching this episode.
ZX Spectrum was my first home computer. Had been using a HP9845 at work (using it to cad electrical schemes) and got the computing bug. The ZX was all I personally could afford at the time and I had many fun moments with it.
 Eventually I started working in the computin business and has been doing so since  then.

[krivx]

I would guess that only the bottom side had a soldermask was because that was the only side that was soldered!

[AG6QR]

I would guess that only the bottom side had a soldermask was because that was the only side that was soldered!

Exactly!

That video brings back memories.  The first computer I owned was a Sinclair ZX81, which I assembled from a kit in summer 1982, for a price just under 100 USD.  It was all through-hole components, and in classic through-hole style, there was a component side and a solder side.  I no longer have the computer, and don't remember details of solder mask, but I suspect it was the same, with a solder mask on the solder side only.

I do remember being pleasantly surprised when it powered up perfectly on the first try after I soldered it together.

That computer only had four chips: Z80, RAM, ROM, and a Ferranti chip to glue it all together.  The RAM was either 1k (Timex later marketed a variation with 2k).  I got an aftermarket memory pack with a whopping 64k of RAM, the full address space of the Z80.

[just_fib_it]

I had one of those too. It kick started my career as a software developer, but sadly also set back my EE career by almost 25 years...

One sad day in 1989 it stopped working, the screen only showing random garbage in all its 16 color glory (or shades of gray in my case). I had recently heard about viruses and worms infecting and damaging computers. Fearlessly I embarked on my first electronics repair attempt. I didn't have a screw driver so couldn't actually open the case but fortunately it was possible to see inside through the opening for the expansion port. Immediately I recognized the problem: my ZX Spectrum had been infected by a worm! I took out my pocket knife and swiftly cut the worm in half, killing it instantly. Unfortunately the worm had already done too much damage and my beloved ZX Spectrum never recovered.

I later found out that I hadn't actually slain a worm but had in fact cut one of the flat flex cables of the keyboard membrane... It took me almost 25 years to recover from this disappointment and rekindle my interest in electronics.

[Salas]

I later found out that I hadn't actually slain a worm but had in fact cut one of the flat flex cables of the keyboard membrane... It took me almost 25 years to recover from this disappointment and rekindle my interest in electronics.

  What can you do, we all started servicing clueless on something somewhere.

I wonder if the solder mask wrinkles shown in the video formed when they soldered  the components than when they tinned the copper though.
ZX Spectrum, ah my first micro. Cassettes and azimuth and nail polish fixing it. Those were the wonder days. C-64 A500 A1200 A3000 later on. O0

[Chipguy]

The 7805 must have had heatsink, that's where the gap comes from. You can still see the marks from the washer on the regulator's tab.

[Orpheus]

My first computer was an Apple II but when the Sinclair came out I removed its board and put in in my car (It was almost a perfect fit for my never-used slide-out dashboard ashtray) and stowed a pop-up Panasonic TV under the dash (fit nicely behind the stick-shift and looked like a speaker when it wasn't popped up)

It had no practical use whatsoever, aside from immense James Bond-flavored freak-out value

[sullyRD]

Nice to see Dave do a Video on the old sinclair spectrum, i love the old spectrums and have a large collection of vintage computers. Dave mentioned that Richard Altwasser designed the layout of the board then went on to work for another company.
He started another company up after he left Sinclair and went into business with Steven Vickers and produced the Jupiter ace.
The Company was only running for two years before it went bust in 1984 and only produced 8000 Jupiter ace computers and 800 Jupiter ace 4000 computers in total It used FORTH as its programming language.
This is my collection of Jupiter Ace computers.


uploaded pictures

[HeyTom]

I had the ti-99-4a. Even had the speech synthesizer. It was very good for its day.

[adeptcs]

I had the misfortune to have repaired hundreds of spectrums in the 1980. As Chipguy says, the ZX spectrum had a heatsink. It went over the top of the edge connector almost to the modulator. It relied on the ventilation of the edge connector which was fine until something was plugged into it.
The most common problem was the ZTX650 transistor giving up, often caused by someone plugged something into the edge connector while it was powered up. The ZTX650 was used in the charged pump circuit to create -5 and +12 in addition to the +5, required for the 4116 DRAM ICs

[VK3DRB]

Notice the clear data codes labelled on the IC's. They don't do that much anymore, especially on SMD components even if there is the space. The data code was a great way to roughly date the manufacture off a printed circuit assembly.

Notice too there is not much attention given to EMC and EMI. It may not have needed any regulatory approvals in those days. I never had a Sinclair microcomputer. I did own a Dick Smith System 80 in 1983, and upgraded it to a Hong Kong made "rotten Apple II" in 1984. None of these machines had any attention to RFI, and as a result they interfered with nearby TV sets. I dare say the Sinclair would have too.

cheers,
Dave