ZX Spectrum 128K "Toastrack" Repair and Jailbar Reduction
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- čas přidán 29. 04. 2020
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I try out a ZX Spectrum 128K "Toastrack" I had bought a while ago. Unsurprisingly it's not working, but it was a really easy repair.
But, once it was working, this particular computer had very noticeable black vertical bars on the screen, also referred to sometimes as "jailbars". So I dive into that and try to improve the video quality by reducing the jailbars as much as possible.
Jailbar reduction on Spectrum for Everyone: spectrumforeveryone.com/techn...
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I'm not even a Spectrum guy, but I just can't stop watching your repair videos. Good to see these neglected retrocomputers finally receive some proper TLC.
It’s nice to see how much things we can still improve over an original design, well done Noel, it was a pleasure to watch again!
Yet another great video from _The Lab..._ Once again I learned something new :D
Try a small ferrite bead inline with 5V right before it hits the chip. I'm working on an external video project for a Mattel Intellivision and I had video noise problems until I started using ferrite beads. They do wonders for cleaning up the 5V rail.
Interesting to see what difference when adding 1uF bypass cap to all DRAM ICs.
Good point. Maybe I should try that in the future and if so post a quick followup video.
I did that as a test yesterday, along with using a 100uf cap in C28. It seems to eliminate the jailbars totally.
Great video!
Thank you for sharing your experiences with fixing these systems.
I agree. Looks much better. Nice job.
My first computer was a Spectrum 48K, Lol. Los condensadores electroliticos pierde su capacidad con los años. Vi en otro video tuyo que cambiastes el regulador lineal 7805 por uno commutado mucho mas eficiente energeticamente, ¡que gran idea!. Buen trabajo como siempre.
Definitely enjoyed that! As soon as I saw the S.A. label on the rear and the keypad, I knew it was the legendary Spanish 128+ because the keypad wasn't really sold in the UK. Good work! :)
Thanks! Glad you enjoyed it.
There are some really good tips here for diagnosing and reducing jailbars. I've bookmarked this video in case I need it in future!
Thanks! I suspect a lot of it is applicable to other systems as well.
Great video, thanks for posting!
Thanks! Glad you enjoyed it!
Great video. And congrats on 1500+ subscribers.🍺
Thanks!🍺😀
Great,as always,video :)
Top notch and informative, even though I never had any exposure in the USA to the Spectrum line (other than some Timex variants) it is still really interesting
Thanks! Glad you enjoyed it.
Good job!
Agreed chainq68k, I am a Commodore person, (VIC-20 was my first PC) But Noel does such a great job explaining what is being troubleshot and fixed/improved that it really does not matter what he is working on :-)
Adding a pi filter at the ULA could make more of a difference. Nice job though. You really improved it
Muy buen trabajo.👍
Separating the two supplies (analog and digital) would be very interesting indeed.
Nice work...
Thank you!
That was a very satisfying repair! The “imagine doing the capacitor replacement 16 times” on screen comment was exactly what I had been thinking when you described that step! 😁 Is the presence of the bars a design error, too much cost reduction in components, or aging capacitors?
Thanks! In general it could be aging capacitors, but in the Spectrum 128K it happens even with new capacitors. I believe it's a combination of not having an optimal layout/sufficient shielding between layers, and today's monitors being a LOT crisper so the bars are a lot more noticeable.
Inductance is often better for removing high frequency noise than capacitance. How about ferrite beads in line with the 5V rail?
Jailbars - I would change the electrolytic to the 47µF and put a 100nF - 1µF ceramic over the power supply pins. If not on the solder side, then there is a nice space on the top between 2 component is glass casings.
nice :)
When you were doing the compare side by sides one with just the caps on the d ram would of been nice to :)
As the noise is high frequency, I would have gone for 470nF. The electrolytics tend to be inductive at higher frequencies.
Nice fix. I think, (but I might be wrong), that one of those tuning cans is for video adjustment to get rid of artifacts. I could be thinking of a diferent model of Speccy though.
Thanks! Those are for the composite/RF video out as far as I know. So they wouldn't affect the source of the problem, which was the RGB signal.
@@NoelsRetroLab Yes, of course, I knew I got something wrong. Sorry about that.
Nice T-shirt :)
Probably you need to change only two capacitors on the ram filtering because you need to filter only the banks that are involved in primary and shadow video ram. Great job with the video.
But that's the thing, those are 1 bit x 64K DRAM chips. They can each only hold 1 bit, so it's not like those two chips hold the video memory. I suspect the reason has more to do with board traces and potential interference more than any digital logic reason.
Well, You are right.
Another nice repair!
I’ve sent you a message through FB about a plus 3
Checking it now :-)
Tantalum caps are beter for smothing, plus ferite inductors and a litle ceramic.
Had a old wersion Spectrum, after half of hour hot as tin roof in august.
I understand cost sawings but regulator in such a smal housing sheesh
Hi Noel,
what a really interesting video this is. Having a nearly _UNUSED_ Toastrack here I was thinking about if I should recap it or not...
I think the capacitors are gone in 2022 and so I'll recap it. I could let you know if the jailbars are also gone after recapping the board.
Thanks for your really interesting videos and have a lot of fun...
MfL der Eratosthenes
Wow, an Investronica Toastrack, no less! Very nice!
On the PCB, what's the large empty circular footprint between the DC input jack and the ROM for? I can't quite work it out...
You know, I don't know! It says "toroid" and it's huge. So it was probably intended for some kind of inductor or transformer, but obviously it was never used.
@@NoelsRetroLab A bit late but you might still be interested: That's where a common mode choke would have gone, but they probably decided it was too expensive to include in the end. It would have added a bit more filtering to the input by attenuating noise which occurs equally on both power lines (hence "common mode"). You can often see on old boards where there's a space for one but it's not mounted.
Spanish Investronica Toasty with the keypad!
with a Derby rom
My money is on the regulator.
Yep. You can use the tab on the regulator for ground because it's common to the ground on the 78xx series BTW.
Great video!
Yup :-) I wonder if the UK version has the same jailbar problems or they changed some of the PCB so it creates less interference.
Noel's Retro Lab the jailbars on spectrums vary from each individual machine to the next. Getting rid of them is kind of an art rather than a science as you showed!
Hello! Congratulations for your video. Is possible to find a Amstrad 40077 gateway array for spectrum +2A? Thanks in advance
Thanks! I don't think those ULAs were ever reverse engineered and recreated (check to be sure). If so your best bet is to find another beat up Spectrum as a donor for that part.
Running diagnostics wouldn't hurt and it could reveal more problems.
Yes, totally right. I did that off camera and they passed. I didn't add it to the video because it was getting long enough, but I totally agree that you can't just see the BASIC prompt and call it good.
you need to add 100nf caps to clean the signals
I still have my toast rack 128K Speccy. Not sure if it still runs, it may need re-capping. I've had it since they were in the shops new.
In my experience hte 128Ks almost never need recapping because the heat dissipation was really good. So you may be lucky and have it just work. Give it a try!
Yes, re-capping is more like prevention and future-proofing. I've recently seen two toastracks, still with the original caps and they worked flawlessly. No need to rush, better find someone who is really skilled at it. Also, it's possible to install (in a non-invasive way) something like TRACO TSR 2-2450 instead of the original 7805 voltage regulator and that will improve thermal management even further. I think the #1 reason of capacitor failure was heat rather than age, especially in 48K Spectrums. But of course, they are not going to last forever.
13:17 I'm sure my +3 is less noisy than that when using RGB scart. I remember being able to see the pixels - so the picture looked quite blocky on an LCD.
I found an old picture I took using the test card (hold break on boot), I can email it over if you want to see the difference?
I suspect it depends a lot on how sensitive the TV is to that kind of noise. On my CRT, I could swear the image was razor sharp, yet it looked pretty bad on that LCD. Maybe other LCDs are different? Or maybe my power supply is introducing all that noise and needs some recapping. I'll probably make a video when I look into it.
Thanks, but it won't help too much because of the different LCDs. However, if you have a scope I'd love to see what the RGB signal looks like on your Spectrum. That way I'll get an idea if that's normal or mine is particularly bad.
@@NoelsRetroLab Hello Noel. No sorry I haven't got a multimeter. The motherboard is a Z70830 issue 2. I'v owned it since 1992 and apart from one trip to the repair shop in 1993, it unmodified, except for the "guesser" sound modification.
@@NoelsRetroLab Hi Noel. Here's my grey +2 before modding, it has really noticeable jailbars photos.app.goo.gl/WCC4ecsVqvzgXzBW7
where did u find the zx spectrum numeric pad? amazing!!!!! at 0.51
It came standard with all Spanish ZX Spectrum 128K models. I believe it was never sold in the UK though.
@@NoelsRetroLab i want one for my +2
Please make another video explain how to make this in the noisy ZX Spectrum +2A/B +3 video output
That's not a bad idea. I'll look into it. I always thought the image quality was great until I saw it on that LCD and then I realized how noisy it was.
Often it's enough to just remove C24. It will detach audio and video carrier signals. You'll lose the ability to hear sound through RF modulator but who uses that anyway... :) Or maybe just use RGB out.
Never leave the old buffer capacitor in it! Take out a new one. May cause problems ... (swelling, short circuit)
With my 48K speccy I replaced the 7805 with a Recom 78E5 (It's a teeny tiny switchmode PSU in the same form factor as the 7805) which generates virtually no heat. I think I saw that on Ms Mad Lemon? Makes a huge difference to the heat. Not sure if it would add noise or reduce noise though. (Digi Key Part No: www.digikey.com.au/product-detail/en/recom-power/R-78E5.0-1.0/945-2201-ND/4930585)
Yes, I also use similar ones (TRACO Power) like in my Speccy tune up video and they're great. But I don't think that will help here because the noise isn't coming from the 7805 (I don't think!), but from interference from other chips. It would be a good experiment to run though.
try 100nF for HF Bypass
My Grey +2 has a mild case of jailbars through the RGB. Does anyone know a similar fix?
I haven't done it, but the 128K grey happens to have the same ULA as this one. So maybe a similar approach will work, especially the 2 electrolytic capacitors in the +5V pin of the ULA.
@@NoelsRetroLab Good idea, I'd also be interested in a fix for this, my Grey +2 has bad jailbars despite recapping and all known fixes having been applied. I'll take a look at the 5v rail caps and see if it helps.
Hi, I have just adapted the fix for the Grey +2 Issue 3 and it eliminates Jailbars totally, Swap C52 from a 22uf capacitor to a 100uf Capacitor.
Add 8 1uf ceramic capacitors in positions C12 - C19. I have all the details in my channel.
@@jamhamster That's great to hear! I'll go check out the video now :-)
@@NoelsRetroLab It has been driving me bonkers for years but the odd thing is than now I have a near perfect image I sort of miss the artifacts. Mine isn't the best produced video but you can't argue with the results. :-)
Hell ! can you help ? i own a zx spectrum sinclair 48k that doesn´t load the games. They just get errors when first game screen opens or crash during the doalings and green little squares on some loading drawings. I inserted that to check the upper RAM chips :
PRINT PEEK 23732 + 256 * PEEK 23733 the value result was wrong
it was 32863 instead of 6553 »»»» I tested all the 8 upper RAM chips group on the board below (right side not the logical ones) using a fully working sinclair 48k and all 8 are good.
oh my god where is the menu ? lol "tape tester" etc ?
What spectrum is that?
I have a 128k toastrack and it has that menu like the later models +2 +3
This was the Spanish Investronica version, which was released first and didn't have those fancy menus yet :-) They updated the ROM for the UK release, and I believe they fixed a few bugs along the way.
Where do you get the T-shirt from?
One of those sites that prints custom t-shirts. I think it might have been this one: www.latostadora.com/web/sinclair_zx_spectrum_-_logo/1078007
@@NoelsRetroLab Thanks, ordered! :-)
@@schmelpe They also sell them at Etsy I think.
Why are those linear regulators always supplied with twice the required voltage?
Normally linear regulators need to have an input 2V higher than the output. The Spectrum ones are supposedly 9V and output 5V, I suppose that's because they couldn't make 7V-8V power supplies easily and 9V was more standard? However, they often read 12-14V when they don't have a load, but once you plug them in they go down to about 9V as expected.
@@NoelsRetroLab They could have used a switching DC to DC converter.
@@zachz96 Maybe in the 80s they were either more expensive or really noisy. Not sure. At least with the Toastrack they finally got the heat dissipation right. Other earlier models always get too hot.
oh yeah.....i can still see the lines
Just put 10uF 0805 smd cap!
You can also put caps like this:
i.postimg.cc/8PHTZy2X/cap.jpg
Yes, that's how I put the radial electrolytic capacitor that was replacing an axial one at 19:45 :-)
@@NoelsRetroLab Too fast for me, can't see more than 25fps :-D
I wonder can something be done to get rid of that "jailbars" in case of old ISA VGA cards? Have a look at the screenshot: shrani.najdi.si/?2D/f5/4edMkt9c/wolf3d.jpg
I suspect that's something different. VGA has a digital signal, so it's not a matter of adding capacitors. That looks more like a problem with that particular TV set I'm afraid.
@@NoelsRetroLab not exactly: "Unlike the cards that preceded it, which used binary TTL signals to interface with a monitor (or composite, in the case of the CGA,) the VGA introduced a video interface using pure analog RGB signals, 0.7 volts peak-to-peak max."
have lots of parts computer store buddy is stoping lots of old parts good and for free
They should have terminated the signal lines properly. Reflections and impedance mismatches abound in these cheap computers.
Way too much thermal paste used there, you used almost as much as you would use on a modern CPU! LOL Half what you used would have been plenty for the regulator 🙂
Yeah, you're probably right 😃
I still don’t understand why pc companies just don’t put all the components in a pc, you know?
You get your new… i dunno, 10 sata drive to PCIe 2, and you see a s*it ton of traces to put components, but the components are not there, JUST PUT THE COMPONENTS IN THERE OR DON’T DRAW THEM ON THE BOARD
Ugh it’s so annoying to me, like if it’s also annoying to you