Fixing Bad Video Quality on the Sinclair ZX Spectrum

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We have two Sinclair ZX Spectrum+ computers with REALLY bad video image quality. This is a pretty frequent fault and is usually caused by bad electrolytic capacitors generating unstable voltages inside the computer. Here we learn how to diagnose and fix the bad video quality caused by the capacitors.
We take a good look at the voltage-generating circuitry inside the Spectrum (it generates +12V, +5V, and -5V from a 9V DC power supply) and try to understand how it all works. Then we take a look at the voltage signals with the oscilloscope and confirm that the electrolytic capacitors are most likely faulty.
Finally, we replace all the electrolytic capacitors, measure everything again, and test the final image quality and compare it to how it was at the beginning.
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3 июл 2024

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Комментарии : 58

@robertlinder6414 2 года назад

Great way to teach electronic to folks and be amazed by what a few chips can do.

@Xoferif 4 года назад

Your workshop is unreasonably clean, tidy and organised! =)

@NoelsRetroLab 4 года назад

Hahaha... I won't lie: I like it that way. But even if I didn't, I have to keep it that way because I have a very small space. One day I'll do a mini video with the "tour" of the workshop/office.

@melanierhianna 2 года назад

Isn’t it. I work from home and my space is a mess, covered in prototype hardware, breadboards etc. All things I’m working on for my employer.

@AngeloCoelho 4 года назад

At least someone who did a recap, but, showing technical information, and how it could affect each circuit. Not like a lot of idiots, who don't even know anything about electronics, watch youtube videos and feel like gods of electronics, and every single device, for them are bad caps, "need recap" ! Great job Noel ! I'm an electronics Tech as well !

@NoelsRetroLab 4 года назад

Thanks! Yes, one of the goals for the channel is not just teaching people how to do things, but to have them learn WHY they're doing those things :-)

@annieworroll4373 9 месяцев назад

A video problem was the first computer repair I broke out a soldering iron for. My TRS-80 Model 100 arrived in mostly good condition, but the display flickered pretty badly. A few electrolytic capacitors had failed. Thankfully, it was easy to visually diagnose it(and some web searches pointed to failed caps being a common cause of that sort of flicker) and get the display rock solid like it should be.

@hugocosta4437 4 года назад

Awesome video! I've recently bought a zx spectrum + with that exact simptoms and now I know where to start to try the repairings. Thank you

@NoelsRetroLab 4 года назад

Great! Replacing the capacitors is always a safe move and a great way to start. Check out my Tune Up video though, because some board issues have the wrong polarity marked on them, so you should always follow the polarity of the capacitor you extracted, not what's printed on the board!

@KolliRail 4 года назад

Another very useful video with good explanations!

@MajorTomWorkshop 4 года назад

It's quite interesting actually, I didn't know the original Spectrum had a voltage inverter. The Soviet clones of Spectrum widespread in former USSR (which I'm sure you are aware of) used the 4164 DRAM chips (Russian clone name К565РУ5) that were 5v powered and did not require 3 voltages to power. Also they used RGB output that TVs had to be modded for, hence, no RF modulator and AV output. I recentley purchased a 48K Spectrum on Ebay and I'll be aware of this problem now, thanks much for your video!

@NoelsRetroLab 4 года назад

You're welcome. I didn't know the Russian clones used 4164. That would make so much sense! Is the memory organized more like in the 128K, or do they still have a separate bank for video RAM to minimize changes from the original?

@MajorTomWorkshop 4 года назад

@@NoelsRetroLab Yes, they do have a 16K bank for video RAM (as far as I recall it's only partially video and it's up to 0x8000 user RAM) and 32K for the rest of memory. Also, RAM performance is different in these two banks, I think original Spectrum has that effect too. As a teenager I used to write custom loaders for games, I tried to port the tape loading routine into RAM and it wouldn't work in the lower half because of screen addressing CPU cycles. )

@frankowalker4662 4 года назад

Just found your channel, good stuff. About the time you made this video, I was re-capping my 48K and 128K +2.

@NoelsRetroLab 4 года назад

Thanks! The +2s don't have as many issues with the capacitors because they run a lot cooler, but yeah, the poor 48K, especially the Plus ones, almost always need a recap.

@frankowalker4662 4 года назад

@@NoelsRetroLab The +2 kept crashing, resetting or sometimes there was an audio click and the picture went fuzzy. LOL. But works a treat now. I've had two of these for decades now, but this is the first time I've ever seen anything like it.

@10MARC 4 года назад

Quite a difference those capacitors made! Nice job!

@NoelsRetroLab 4 года назад

Yeah, seriously! I don't usually advocate changing capacitors just for kicks, but these poor computers really needed it!

@federicoachaerandio2698 4 года назад

Great video. Thank you!

@ncbrady 4 года назад

Interesting video Noel (as always). I'd like to see a video from you explaining how to determine what a capicator's rating is and what type of new capacitor is suitable for replacing it with, thanks Noel !

@NoelsRetroLab 4 года назад

Thanks Niall! There's not much to the capacitors: Use the same capacitance than the one you're replacing (the number in uF usually), and use a voltage the same or higher than the one you replaced. That's it. Now, figuring out what capacitors to put in the first place when you design a circuit, that's much trickier and I don't even have enough experience to figure that out :-) Hopefully I'll learn that when I get more into designing my own boards.

@campallu 4 года назад

Just wish youtube and your channel existed 35 years ago... Miss my ZX and Horace game.

@NoelsRetroLab 4 года назад

Haha! But that's one of the things that makes retro electronics so compelling today: The technology we have today lets us interface with old technology like this quite easily and cheaply. 35 years ago it was state of the art and quite difficult to do a lot of these things :-) As for your ZX... it's never too late!

@AnotherUser1000 3 года назад

You can always find your beloved games, here: worldofspectrum.org/archive/software/games They changed the layout of the page a lot, since the '90s, but you can find it there. And then, you can just download an emulator and play it! Tell me if I helped you in any way.

@retrogamer33 3 года назад

I forgot about the centre negative on the Spectrum, plugged in a 9v centre plus and bang went the regulator and coil

@CaptainCarling 3 года назад

Just done exactly the same thing, do I need a new regulator?

@carnright 3 года назад

Hope you are not getting tired of me saying this is a great video showing how using an oscilloscope can be very useful. Is you shirt a H.P. Lovecraft reference :-D ?

@NoelsRetroLab 3 года назад

Of course not! Happy to hear you're enjoying the videos! 😃And yes, you got the reference! Most people don't get it.

@carnright 3 года назад

@@NoelsRetroLab LOL I'll keep my eye out for a Miskatonic University as well :-D

@NoelsRetroLab 3 года назад

@@carnright Haha, that's my wife's t-shirt (sometimes we wear them when we play Arkham Horror for extra immersion 🤣).

@cygil1 10 месяцев назад

I have this exact problem, with the exact same interference pattern as the first machine. It also wont load from tape at all, and my theory is that all the noise in the video rf generator is polluting the sound demodulator as well.

@ct92404 3 года назад

Ha, I like that effect at the beginning!

@NoelsRetroLab 3 года назад

😁

@sashaerceg 2 года назад

Nice work! I have fixed image on all Sectrums that way. But I can load games only from tape player or strong audio out, and not from any phone or audio player. Maybe you can make video about that fix. Thanks

@spinnetti 3 года назад

Does this apply to the TS2068 too? My composite out is quite noisy

@u3b93 5 месяцев назад

ZX Spectrum 16K, 48K, and ZX Spectrum+ 128K, +2, +2A, +3 CPU cycles per PAL line 224 228 PAL line time 64 μs 64.28 μs PAL lines per frame 312 311 Frame time 19.968 ms 19.9915 ms Frame rate 50.08 fps 50.02 fps Display Vertical Synchronization by the Z80 maskable interrupt line

@ElectronGordo 4 года назад

Noel, could you put the cost of the traco Power? Or the link from where you got it? please. Usually the price is pretty more expensive than xx05, or a DC-DC Converter, but if it is worthy and prices not too crazy, could be a nice replacement. By the way... one Amperes is enough? Thinking about to plug some devices... not sure about 1 or 2 Amperes to choose in my case.

@NoelsRetroLab 4 года назад

I got mine from an order I placed on Mouser a while back: eu.mouser.com/ProductDetail/traco-power/tsr-1-2450 It looks to be 5,50€ plus shipping. I wouldn't be surprised if you can find cheaper sources. There's a small DC-DC converter that's pretty inexpensive and other people swear by it, but I haven't tried it yet.

@SueTownream 3 года назад

Very nice music at 11:05. What track is that?

@SueTownream 3 года назад

Found it myself: opengameart.org/content/theme-song-8-bit

@CaptainCarling 3 года назад

I've just got my old 48k down from the loft which I had as a kid in 83. One of the two caps you said fail often had died so I replaced it. I have done the composite mod as well, but the display is very very poor. I plugged a different power supply in without realising the positive and negative were the wrong way around (modern way around) which I think has blown something, any ideas where I should start looking?

@NoelsRetroLab 3 года назад

Yes, check out the DC voltages, especially -12V in the PAL encoder (I think I have some videos exactly about that). Chances are the transistor TR4 (or TR5) is blown and not getting steady 12V. Hopefully that's all it is, although it's hard to tell the full extent of the damage ahead of time.

@CaptainCarling 3 года назад

@@NoelsRetroLab I've ordered TR4 and TR5 Transistors and also a modern voltage regulator, I'll replace them and hopefully she'll wake up

@ITGuyinaction 3 года назад

🤘😁🤘

@Lilithe 3 года назад

Probably nuked my Sinclair Z81 as a kid plugging it in while the power brick was plugged in. I bet I could fix it these days but it's of course long gone.

@NoelsRetroLab 3 года назад

I don't think plugging it in while the power brick is connected should be a problem. The usual problem is connecting something to the expansion port while the computer is powered. In any case, chances are it was an easy repair. Maybe it's time to get a ZX81 back 😃

@watchmakerful 3 года назад

My first thought when I saw this video noise: dirty power...

@NoelsRetroLab 3 года назад

Definitely. Especially on the PAL video encoder it becomes very visible.

@watchmakerful 3 года назад

@@NoelsRetroLab It can happen even on VGA.

@gyulaszabo6750 3 года назад

ohh.. Philips capacitors... time bomb :)

@NoelsRetroLab 3 года назад

Oh really? I didn't know the Phillips ones were particularly bad. I'll keep it in mind. Thanks for the tip!

@gyulaszabo6750 3 года назад

@@NoelsRetroLab Philips capacitors are very good, but after 20-25 years their condition deteriorates a lot. They are not dealing with the heat, but with the pulse load. (I'm upgrading old Philips CDs, all need to replace the capacitors)

@hugocosta4437 4 года назад

I have a suggestion for a video. Updating the ram on a 48k Spectrum, transforming it in a working 128k. I found a page explaining how to to it but, unfortunately, is to complicating for my knowledge. hw.speccy.cz/128krebuild.html

@NoelsRetroLab 4 года назад

Interesting! I had seen some Spectrums upgraded to something like 80K or something like that, but I'll have to look into that. Thanks for the link.

@hugocosta4437 4 года назад

@@NoelsRetroLab And if you want to build the ultimate Spectrum + 48k-128k, it is also possible to add the AY 3-8910 Sound Generator Chip with stereo output. lotharek.pl/productdetail.php?id=229

@luispanaderoguardeno3306 2 года назад

@@NoelsRetroLab I remember my father telling me, how he upgrade his 48k Spectrum to 80K. He replaced the "faulty" 64k upper rams for true 64k ram chips, and added a switch to toggle between the two 32k pages. Crude, but worked. I think that the next step would be adding some logic to switch banks , writing to a I/O port.