Sinclair ZX Spectrum+ Garbage Screen Repair
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- Опубликовано: 11 июл 2024
- Troubleshooting and repairing a Sinclair ZX Spectrum+ (issue 4A mainboard) that displays flashing garbage patterns on screen and does not properly start up.
The Speccy was kindly donated by www.gee-k.net (check out the website for tons of vintage computer tinkering and more).
You can watch my restoration of this Spectrum+ here: • Sinclair ZX Spectrum+ ...
My ZX Spectrum composite mod tutorial video: • ZX Spectrum 48k Easy C...
The DivMMCfuture is available from The Future Was 8-Bit here: www.thefuturewas8bit.com/shop...
The MeanWell power supply I used is available here* (REMEMBER TO REVERSE THE POLARITY!):
US: amzn.to/2lKv4sb
UK: amzn.to/2li2tdC (a slightly higher rated one)
DE: amzn.to/2kcaEaY
The ZX Spectrum Diagnostics software is available here: github.com/brendanalford/zx-d...
The (brilliant!) Return of Traxtor game you see me playing during the credits is available from the author's website here (among many others): www.usebox.net/jjm/return-of-...
--------------------------------------------
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Thanks for watching!
* Stuff marked with "*" contains affiliate links. You don't pay anything extra and I get a little commission from everything you buy through the links (even if you buy something different there).
TIME STAMPS:
0:00 Introduction
1:46 Disassembly & Inspection
7:08 Composite Mod
10:10 Power Supply
10:41 Garbage Screen
11:08 Cleaning RCA Connector
11:35 Checking the Voltages
14:05 Replacing the Voltage Regulator
17:58 Different Garbage!
18:23 ULA Fault?
20:53 Piggybacking RAM
24:00 Replacing RAM & Touching up Solder Joints
31:15 Testing
31:53 Replacing the Keyboard Membrane
34:28 Final Testing
36:28 Thank you & Goodbye
#JanBeta #ZXSpectrum #Retrocomputing 
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Ahhh ... The Plus ... what memories it brings :-) I used to have two of them in the 80/90-ties ... I was responsible for them on a series of youth camps and shared my experience and ... games with the kids ... I’ve felt like a guru ... :-) And had to fix them on the field ... :-)
And now - I’ve collected 5 or 6 Speccy Plus machines - each in excellent condition. Most of them in the original setups (with cassettes, manuals and boxes)🤪
You should sell some to let others experience them. You would get good money you could use for something else. I have a few spectrums but nome in box etc as you pointed out and few duplicates apart from a group of 48k units in rough condition
Amazing to see how much love you put in these machines.
Awesome stuff. Made me smile watching that.
Glad i put that membrane in there too. Had a feeling it would be like the other two i have.
Your videos are always both entertaining and informative. I feel like I've learned so much, and actually have the confidence to start fixing things of mine on my own! Thank you so much for the inspiration!
Oh, glad to hear that! Much luck with your future projects! :D
You got just one of the best retro repair channels i have seen!
The ZX Spectrum + you could get them in kit form for £39.99, well that's what mine cost back in the day, it came with very simple instructions and it was pretty easy to upgrade the rubber key version to the ZX Spectrum +. And thank you very much for the video for bringing back such wonderful memories
if anything sir Clive Sinclair was ,he was a design genius , that STILL looks cool today !!!
Rick Dickinson was the design genius. ;) en.m.wikipedia.org/wiki/Rick_Dickinson
Sir Clive Sinclair did not design the Spectrum
Nice one, Jan. Piggybacking RAM ICs always is a quick and handy RAM diag technique. Great fix again, sir! Looking forward to part 2.
Thanks Mark! Piggybacking has been pretty hit and miss for me in the past. But this time it worked flawlessly. Definitely the easiest way to troubleshoot this machine without a diagnostics ROM. :)
nice video and impressive that you were able to repair it with just a meter and no scope etc
Another successful fix! Good job!
Will watch after work tonight. Great stuff :-)
Hope you enjoy it! :)
That was Great Jan. i am working on a 128k + at the momemt. Keep up the good work . All the best.
Nice fix. I STILL need to add a Spectrum to my collection. 😀
Liked for your choice of Joystick, those TAC-2's are great, virtually unbreakable and silky smooth to use.
My favourite joystick these days! :)
I see a sign .......at around 13:10 when you show your phone the time is 1541......the universe wants you to do Commodore videos. :-)
Wow, didn't notice that. Weird coincidence! (Or a sign from the universe?!)
Well done Jan! I'm enjoying working on the Plus's recently, I find the keyboards very satisfying to disassemble and clean. I have the same issue with the Return key sticking down but I find after a clean it gets "good enough", I do think you would need a new, springy, "rubber bubbles" part to fully resolve it.
Sir Clive has always been a big fan of "looks" rather than quality. I agree with you on how good and timeless designs they came up with all the computers they made. But, when you look deeper, you can easily see the low quality manufacturing, inferior parts used, shortcuts they took to solve problems stick out like a sore thumb. Always been a fan of Spectrums, especially 48K models and it is great to see them come alive. Great video as always!
Yes, they were definitely built to a price. But in the end, I guess that was a huge part of their success. And Sir Clive seems to always had the "computers for the masses" thing down even more than Commodore's Jack Tramiel. At least the machines were sold even less expensive. :)
I have uncomfortable memories of this computer, playing on my mate's spectrum+ one day I pushed the computer back in anger at losing a game of something. I think I dislodged the joystick interface or something, black screen and it never worked again. I was not popular at his house. If you ever read this, I'm still sorry Ben, haha!
Uh, that sounds horrible. Thanks for sharing the story! :D
That was a common problem, I think if you slightly dislodge the interface then it sends 5v down the wrong lines. I used to work in a computer store on a saturday (in my teens), and the owner made a lot of money from repairing broken spectrums where that had happened. Most of the time the owner had done it by plugging in the joystick port while it was on, pushing in the connecter which would push out the interface, but i'm sure there were a few anger incidents too.
It's actually the 12 volts used for the 4116RAM and the PAL encoder chip. For some reason this is also present on the expansion connector. ( Maybe for the ZX Printer?)
Great to see a Spectrum brought back to life! I seem to remember that the last models of the Spectrum+ don't suffer from the keyboard membrane rot. They're the ones made in Korea by Samsung, and the membrane is made of the same sort of clear plastic as the modern replacements. I think I have one somewhere, but I've lost track of my disorganised collection.
Ah, that might very well be. I remember seeing rubber key Spectrums produced by Samsung with slightly changed design (and maybe better components?). They are quite sought after I think.
@@JanBeta I didn't realise they made the rubber-keyed ones in Korea too, but it makes sense as they produced both models alongside each other at two different price points. Better components also seem likely, as I think the reason that they started producing them in Korea was that the earlier ones were extremely unreliable, often being dead on arrival or breaking within a few days of purchase.
I gave you the 1000th like ! Yes it was me :) remember, you can always check the ram chips with your TL866 mini pro.
Good job Jan!
I've replaced the 7805 with a recom switching regulators (I know you love them too) to get rid of that bulky heatsink. And then a power switch.
Yes, I need to do that some time, too. Although I think the larger case of the Plus at least allows for a tiny bit more airflow than in the rubber key models.
Nice work! One day I'll get one of these machines myself :)
Thanks Robin! The Spectrums are really charming machines. Can recommend. ;)
I used to own a 48K rubber key Spectrum and a 128K Plus model, well still do own them just not risking powering them up! I am now the proud owner of the new ZX Spectrum Next which has more modern styling based on the Plus model, same guy designed it, Rick Dickinson, who sadly never got to see the Next released.
Yes! The next is an awesome piece of hardware (didn't have the chance to meet one in person yet though)! I think if you take some precautions (especially not using the standard power supplies) with the Speccys, they are pretty safe to power on. The RAM usually fails at some point with age and the capacitors are going to need to be replaced though.
So glad the Spectrum Next uses center positive on the DC jack
Kind of confusing but definitely the better choice for a modern system. :)
Cool video. Check the alignment and pressure on the membrane tails as they can be fickle. It is a three layer membrane and needs to be clamped carefully. Also the perished foam was to prevent the membrane shorting against the metal.
Good point! I’m going to take extra care when I get into fully refurbishing the machine. Thanks! :)
Love ur vids man! If I were to criticise one thing tho it would be just to add a compressor to your microphone. Your speech is very dynamic.
Thanks! There is quite some compression on the mic already, but I tend to mumble a bit at times so it's not enough. I'll try to compensate for that more in the future.
Nice repair and another saved spectrum. But I would recommend to do the composite video mod with a 10 µF capacitor instead of a simple wire. The wire works, but the output includes a huge DC offset which can cause disturbances.
Behold!!! The good looking Turdtrum+... 😁
good work fault finding i saw this preview on twitter yesterday arvo i knew it was coming soon
i saw you were rendering it. next time youll get more ideas you can fix membrane dont need to buy new keypad fix connectors easy . good work again bye
Never had a plus, just a rubber keyed Speccy. In the late 80's I got a +2A for my birthday, the best thing about them was to program in basic (at first) the brilliant book with the orange sunset cover, Wass amazing, and it was my book cos mom and dad didn't understand it. Loved the machine dearly.. still trying to find a decent 48k rubber keyed Speccy that isn't silly money
Great to see someone on RUclips using an anti static wrist strap - although it's bad practice to power up a board on the anti static mat. Also whilst not critical in this application, it's not good practice to apply heat sink compound with your finger! Finally worth nothing that every 48K Spectrum shipped with faulty memory by design - (Sir) Clive Sinclair purchased all the faulty 4116 memory chips he could (they are actually 16K memory chips) as he discovered it's the upper 8K that was faulty and so the 48K Spectrum's only access the lower 8K of memory in those chips - imagine if you could access the full 128K back in the day!
Worth noting why there is poor soldering on those chips, if you check the circuit those bad joints are actually just pads - the upper memory mapping wasn't used - that's A4, A5 & A6 which correspond to pins 10, 11 & 13. They where also hand soldered in place as they couldn't tolerate the wave soldering technique...
The 4116s are 16 kilobit chips as far as I know, they are fully used. 8 of them make up the 16 kilobyte of lower RAM. They used the half-broken RAMs for the upper memory to my knowledge.
Good point with the ESD mat, didn’t have any problems with it yet though, fortunately! Thanks for pointing that out.
@@JanBeta Ah I remembered it wrong (it's been nearly 40 years!). It was the 64K chips with the either one or other of the 32K banks used - there is a link on the board to select which bank.
Ooh, I have to take exception to you saying the Spectrum's ULA is "like the C64's PLA"! It's a much more complicated chip than that!
Apart from that, a very enjoyable video. =)
Yeah, that's true. It does more than the PLA. :)
Reminds me to get a DivMMC future for my 48k :D
I really love your videos Jan, keep them coming :)
I think the reset switch just lifts out, rather than needing to desolder it
Ha! That might very well be the case, didn't realize it obviously... :D
@6:30 Was saying the same thing. It just lifts out.
@@gertsy2000 Me too! Sometimes watching tech videos you just want to yell at the screen and hope somehow magically the person in the video hears and realises their mistake! lol
OMG who puts thermal paste on their fingers?
Nice job Jan :) It's kinda weird seeing a 48k board which hasn't got a bodgefix on the z80 lol
The spectrum should run perfectly fine on 4.9V by the way.... Most of the chips are TTL and the 5V spec is generally 4.75-5.25 for proper operation. Older 7805's are generally not that accurate. Using the Recom, Tracopower or Murata replacement modules is a very good idea though
Was coming to say the same. 4.92v is still 5v in my book. :)
Yes, I know about the voltage. It still seemed suspiciously low to me (compared to other Speccys) and I also measured a voltage spike of around 8V on the 5V rail after turning the machine on. I might use one of the replacement modules, the 7805 gets quite toasty (although the larger case of the Plus model seems to help with the airflow a bit). :)
Ich habe bis jetzt nie darüber nachgedacht. Undichte Kondensatoren riechen wirklich nach Fisch. Haaaaa Anyway good to see another spectrum still goin' even if you had to basically redo the entire board of solder and cap replacement to get it, but that's why it's fun. Danke Jan!
Thanks! Yes, more work to be put into this but I think it's definitely worth it. :)
I have the same computer with the same fault. Now i know what i have to do thanks. 👍
Hope you manage to fix it! 🤞
@@JanBeta Thank`s 👍.
I will need to order some ram chips or remove some from one of my Spectrum.
Contact Cleaner and a plastic brush, two things i can't manage without.
and your ground strap, and to make sure your brush is connductive
I didn't like Spectrum, but I grew up there.
But always found them under powered shall we say was pure commodore here in the Netherlands in England they were very popular.
But I still appreciate your Spectrum videos to see that technique with those crappy membrane keyboards.
But you were lucky again with an extra membrane, which is great.
WRONG.....the Spectrum has the faster Z80 chip at 3.58mhz compared to the C64's puny 1mhz .
yes the c64 has dedicated graphics stuff but a decent speccy programmer can utilise several 'tricks' using 'interupts' etc to make games FAR superior to the c64. one of the fastest 8bit games EVER made was 'Darkstar' on the speccy........try doin that on a C64 !
@@martinparker6536 see that only real hardware man can know. that of c64 only had 1 mhz I knew idd c64 uses a lot of stuff.
my friend was the first in the world who managed to remove all borders on the c64 sprites in the borders all borders was in collaboration with the 1001 crew guests that I could get in 1984 because my software was always good times that heights of the c64. gr
thanks for the suit on my pants :)
Which thermal paste are you using for voltage regulators?
i need a keyboard membrane replacement too for the Spectrum+, where i can find some? is too expensive?
This seems to be a recommended replacement membrane (I don't know where mine came from): www.sellmyretro.com/offer/details/brand-new-%282016%29-sinclair-zx-spectrum%2B-48k~~128k-keyboard-membrane-17350
Can't recall but shouldn't there be a de-coupling cap on the composite out mode wire? I always put a diode on the bacl of the board near the power jack to stop them getting shafted by reverse voltage in the future lol. Keep it up.
WRT to 7805, it might have oscillated at start.
YOu could add 100nf on the chip between pin 1 and 2 and other betewwn pins 2 and 3.
And always bend piin with tweezers.
Doing it your way can crack the plastic and enable water to get in from air.
I liked your little trick you did when you cut the RF loose and tied in the composite signal. Does your LCD support a composite connection or do you have it running through another adapter?
I'm using a cheapo SCART to HDMI upscaler that I modded with RCA inputs for testing (there's also a video about the mods on my channel). The quality is not great but good enough for testing.
Awesome 10/10 ,so was this version of the spectrum the same pcp as the first version?
Yes, they used the later revisions of the rubber key Speccy boards in the Plus. They all have 48k RAM and they added the reset switch, otherwise the boards are the same.
I've got one of those desoldering tools too, but once I have identified a RAM fault I tend to use my hot air desoldering tool to take out all the RAM chips
the hot air desoldering doesn't seem to cause any immediate problems with the still working RAM, and only takes about 30 seconds per chip...the harder part is to clear the vias of solder which I find is easier with a traditional solder sucker n iron
result is all RAM is then socketed, looking nice and uniform and if you have more faulty RAM than originally expected, its easy to swap those out to test on a known working machine
Oh, interesting approach. Didn't think of using hot air but it makes sense if you want to desolder all the RAMs anyway.
Is there not a correct membrane available for the Plus?
At least in the 80s, the keyboard membrane usually cracked right at the end where the connectors to the PCB are. Just use a scissor and cut of the bad end a millimeter after the crack, so the rest of the membrane is still ok. You can do that two or three times until the membrane was becoming too short so you could not close the case. Then you can solder out the connector from the PCB and extend this with some ordinary wires to the PCB and glue it to the lid (be careful that this manually still fits all together). You know, back in the 80s there was no way to buy a new membrane ...
I'm excited to get home and install my vic² mod in my C64. I'm hoping the PAL chip will fix my issues, but somehow I doubt it. Regardless of my video glitching issues, I'll have PAL mode now. I suspect it's one of the logic chips. It wasn't the PLA or the color SRAM. And this time I should be able to work on the C64 without lifting another trace because I forgot to turn the iron temp back down after working on the ground pin.
Ah, yeah, traces are easily destroyed by too much heat. It's always a bit of a gamble with those old boards. Good luck with the mod!
@@JanBeta Good news is the mod works perfectly. The bad news is that PAL is just as glitchy as NTSC. So my VIC was not the issue. I'm not surprised. But since I was going to do this mod anyway, I figured I'd make sure before swapping logic chips. I have 3 main guesses: U16, U26, and U27. But I may order everything. lol......and I'm almost out of solder. I'll have to get more of that too. lol
The Spectrum + is the same as the rubberkey jobs, but they were all 48K and they had the improved keyboard plus reset button. Several companies in the UK offered to convert Spectrums into Spectrum +'s for a small fee
Yes! I think you could also buy a conversion kit for quite reasonable money if I remember correctly. :)
The foam is important - it prevents the keyboard membrane from touching grounded metal surfaces. Capacitive coupling may cause keyboard to "misbehave" when the foam is missing and membrane is too close to the metal.
The reset switch can be removed from the case without any soldering, just pull it up (actually aside according to the switch itself).
Replacing 7805 with a switching regulator is a good idea to limit the heat production and prolong life of a keyboard membrane.
It is also worth to consider replacing a stock ROM with a Gosh Wonderful ROM (you could normally write BASIC commands instead of being forced to use tokens).
P.S.
Try playing Valley of Rains...
Makes sense! I'm going to reapply something in the spots where the foam was. The 7805 is going to be replaced with a nice DC-DC converter at some point I think. I have yet to try the Gosh Wonderful ROM, heard about it before. :)
this is the only computer I have no plans in buying, ever.
Just this Plus version or all Spectrums?
That's ok, they don't make them anymore. :)
I have a 128k toaster rack that has a very strange problem .... some keys dont work
I have put a new membrane and still the problem persists
I have tried inputting directly by shorting each keyboard pins on the board and i dont hear the "bonk" sound for some keys like the arrows
The "enter" works so the 128k goes into "tape loader" but that's as much as I can do...
There doesn't seem to be any corrosion on the board tracks that lead away from the keyboard sockets...
What can it be ? A problem with the rom ? Some data port is shorted ? very strange.
35:30 All keys should work. Make sure the tiny screws on the keyboard plate are not overtightened. I've experienced problems with new membranes when they are overtightened. Screw them in until you feel resistance (don't force it) and then unscrew them half a turn and leave them like that. They should work after.
That is one odd construction. Thanks for pointing that out! :)
@@JanBeta Another thing with the arrow keys, remember that the plastic spacers are also creating contact between the different layers of the keyboard membrane. You might just not have it aligned correctly. When this happens to me, I just loosen the larger membrane connection and push it back towards the keyboard itself. This will most likely fix your arrow issues. It does 100% of the time for me.
Do you re sell these refurbed computers ?
Can you still get new compatible ram chips?
The arrow keys are just mapped to the CAPS SHIFT altered 5 6 7 & 8 keys on the old rubber keyboard. It looked like your SD Card interface was set up to use 6 7 8 9 & 0 which is the Sinclair Joystick standard, the joystick mapping to those numbers directly (without CAPS SHIFT). There were three interface types for joysticks, the main 2 everyone who uses Spectrum emulation knows of are Sinclair and Kempston. The third was called Cursor and simply mapped to the same as the arrow keys on the Plus model, I.E. the CAPS SHIFTed 5 6 7 & 8 with 0 for fire if my memory serves me right.
Ah, makes sense. I still have to figure out if it's just the membrane not making good contact or something. I would guess both keymaps should work in the DivMMC menus.
I was screaming change the 1st ram chip from the time Jan was checking the voltages!!! the hint was one of the pins was at 7v... those chips that atari and sinclair used were a bit crap!
By chance, does anyone know if a wireless sega mega drive controller can be used on the spectrum zx 48k. I'm using a cheap ebay wired one at the moment but it's pretty crappy, many thanks 👍
Can you water cool it?
That glitter probably went in there Christmas day 1983.
lol
What thermal paste do you use on the regulator please?
Oh, it's a standard thermal paste for transistors and such, Felder brand in this case (you can also use stuff for CPUs but that's a bit over the top really).
NOOOOooooo, Jan, stop, it's running The Matrix!
Not only do the ends fail, but the tails develop cracks at bends. The lower RAM can develop faults due to people plugging in joystick adapters whilst they’re powered or wrong power pack usage.
Yes, the tails have cracked on this particular membrane, too. The 4116 RAMs are particularly sensitive to getting the wrong voltages on the 12V rail afaik (that's the actual supply voltage, the +/-5V are for TTL logic only).
19:44 The CPU fills the screen black after reset. In this case plenty of bits are left white, definitely lower RAM.
Yes, makes sense!
Very clever
Appreciate the shorter vid 👍
Thanks! Slowly getting out of "Lockdown Entertainment" mode and trying to do some regular size videos again.
Glitter is small particles, that's called tinsel.
Apart from that decorative stuff, some cables are constructed from what is also called tinsel. Good for flexing, was widely used in telephony. Has to be crimped, not possible to solder unless crimped first (which imo is a bodge).
Yes, I didn't remember the correct word. Interesting that it has a second meaning, too. :)
zx.zigg.net/LRR/ Apparently there's a module that can replace the entire row of Lower Memory on the Spectrum and Spectrum? Haven't seen anyone use it, might be neat tho, instead of having to track down those original temperamental chips.
Retroleum have them as well. They are very useful - a lot less hassle than getting NOS 4116's that dont pop !
Yes, seen those. I think I'm going to get one, makes things a lot more reliable I guess.
I have a +3 if you want it Jan. I was going to do a repair video on it but I never had one in my youth so it's not on my agenda of YT repair videos to do!
Oh, that would nearly complete my Spectrum collection. I have a grey +2 in the queue waiting for refurbishment, too. Would not say no to the +3, they are not too easy to find here in Germany. :)
@@JanBeta I've also got two +2 blacks and a 48k rubber key
@@JanBeta I will message you on Instagram so you can send the address bud!
I'd replace that nasty RCA jack too. lol That thing looks like it's ready to fall apart.
Alse, make yourself a simple logic probe with two leds ( high/low) and small speaker output, so you can hear what's going on.
If you're piggybacking and it doesn't seem to do anything (here it worked though), you can check the outputs with the oscilloscope, you can see the two chips fighting if they don't agree (you get illegal logic levels)
Ah, thanks! That's useful information. I didn't know you could see the chips "fighting". Noted for future repairs. :)
@@JanBeta often you'll get a LOW signal with some super weak signal on there (that wasn't there before). Lift the leg and the signal appears on the piggyback. Also often you get invalid logic levels.
There's one caveat: If the chip is a counter and it is not loaded or reset by the machine, you'll get fighting with working chips because both will have different random states on powerup.
Btw. I'm still missing a Speccy in my collection, but just a week ago I pulled a VIC 20 out of a container. Kernal ROM was bad. Burned a new one and Party On!
Hallo Jan, ich besitze genau dieses Model. Das Bild ist bei mir schlecht bis sehr schlecht und die Tastatur ist na ja... Ein paar Tasten funktionieren nicht mehr.
Kannst mir helfen?
Du brauchst vermutlich eine neue Tastaturmembran und neue Kondensatoren. Allerdings ist das Bild so oder so ziemlich mau bei den alten Spectrum-Modellen.
@@JanBeta Alles klar, danke!
I definitely would've recapped the machine first, even if I didn't suspect that to be the problem. Those cheap 1980s caps are notorious for leaking! If nothing else it would allow the opportunity to give the board a good wash and scrub once the old caps are off, so you don't get that fishy odour later when desoldering/soldering replacement parts.
Yes, definitely going to recap this as soon as possible.
Just a question as a noob that just loves watching this kind of thing. Can you still purchase new RAM chips like these? Does someone still make at least a generic version?
I don't think these RAM ICs are in production anywhere, you can buy new old stock sometimes though. There's also modern replacement PCBs for the Speccys and several other systems that use more modern RAM.
I don't know a lot so please forgive me if this is stupid, but maybe the ULA form the rubber key machine maps the key presses differently to the plus?
i was going to say that...he replaces the ULA with a rubber key one and wrongly presumed they are the same when i think your right .....48k+ ULA has the keyboard mapped differently to use the extra keys ?
The ULA is the exact same version as the one from the rubber key Speccy I put in for testing. The key mapping happens in the membrane actually, as some people pointed out.
@@JanBeta ah, good to know Jan. Thank you
Probably was regular ZX Spectrum 48K with rubber keyboard and later upgraded to + version, cause '+' made in '84. or '85. not shure... ;-)
4.9 out of a 7805 under load is well within spec of the regulator and chipset. If you had less than 4.75 I'd be concerned about the supply. Then again 7805 are dirt cheap and it made you feel better lol
I also measured a voltage spike of around 8V after turning on the power to the machine (it’s in the video while measuring RAM voltages) which led me to the conclusion that it’s better to replace the regulator quickly... ;)
@@JanBeta I suspect that was mostly due to the faulty ram chip allowing part of the +12 rail to pass through or something equally weird especially given the poor solder joints you found on the RAM. If the 5v pin was not properly connected to the 4116 it may allow you to "see" a higher voltage on that pin. I've never seen a 7805 genuinely fail in a flaky state like that where one second you have 8v then suddenly everything is all good :-)
I was thinking the same thing, 4.9 is OK.
9 times out of ten it's dead TRX transistor that is responsible for generating +12V and -5V and/or one or more of the 4116 RAM chips in the first 16K.
With a bit of trickery, they can be replaced with 4164, which is 4x bigger and only needs +5V.
pink glitter is tinsel. Xmas decoration likely :)
Yes, tinsel is the word I didn't remember! :D
Was probably once a much loved christmas present.
Pink tinsel from Christmas decorations.
Yes, I think that's what it was. Maybe the Speccy was a Xmas gift. :)
hi,
what are these speakers ?
The monitor speakers? Behringer MS-20, can't really recommend them but I got them for cheap a couple of years ago.
@@JanBeta ok thx for responde
9:30 maybe it is better to solder first the connector and than the other end (video signal) ;-)
From now on I'll make sure that there is a roll of toilet paper lying around on my work bench.
It's the most efficient way of having tissue on a confined work bench.
I love it. My ZX+ keyboard doesnt work. )o:
@8:43 Jan Beta, you cut your finger on the RF can lid.... Ouch..
No blood though fortunately. But been there before. ;)
Hi from greece, i have one zx 48k , same problem, my zx is like as New,, 2 day before everything was ok, but suddenly occured like this, i knew about the ram, but where are exist this spare parts, ?? Who know !? Pls some one help me?
You can often find replacement RAM on eBay still. Also, there’s a modern replacement PCB that replaces all lower RAM with modern chips. Available from retroleum.co.uk for example.
TSR-1 2450 as usual. Almost no heat.
Build a dram tester...
The membrane uses a original design and they added the cursor keys by adding an extra membrane layer that is electrically connected in the case lid by retaining clips
Just screw the down the membrane retaining clips in the lid to get the arrow keys to work
Not true, the membrane was redesigned for the new keyboard layout. You can clearly see this for yourself in this video if you pause at 32:57, there is no sign of what you claimed at all. And there is no electrical connection to the case lid, it's plastic! The clips are simply to keep the ribbons in place should you need to service the board to prevent accidental pulling on the membrane.
@@TanjoGalbi You are wrong. I suggest you start here www.bytedelight.com/?page_id=6420
if the ula is dead you can get a replacment here zxrenew.co.uk/ZX-Spectrum-replacement-ULA-p151287223 which i used in a +2 grey recenty
I have one of the most impressive Spectrum of all time. There is a 4 compartment Roms in the chip. All together in one Elite 3 keyboard
Compatible with Microdrive, Opus, plus D etc. Unfortunately, everything is already in the attic after a long wait. Various components are likely to be broken. Should anyone find the project worth mentioning to breathe life into this legendary Spectrum, I am happy to send you the PC. I will also be happy to pay for the components, but I will not invoice for work that will finalize your channel anyway. Is it worth it to you?
when you have 6 spare ram chips, why not piggy bag all at once to see if the machine works? Could also identify faulty ram chips for sure ;)
Ah ok, was commenting to early ... :)
no need to dissolder the reset switch it pops out easily.
Yup, I realized that later on… 😅
thats been worked on.. the socketed chip. ..
I think most Speccys I've seen had a socketed ULA (probably because the chips failed so frequently and it was easier to replace them I guess).
@@JanBeta agreed... I had mine (same version) socketed back in the daym it did'nt come from the factory socketed.. . had to have a friends dad do it for me... I managed to get a few ULA's in stash. they were easy to damage by pulling out a peripheral while the Speccy was on. you'd still have a working Speccy.. but you'd lose the ability to use things like microdrives...
@@KhaiJbach I'm pretty sure most were socketed from the factory. Take a look at k1.spdns.de/Vintage/Sinclair/82/Sinclair%20ZX%20Spectrum/PCB%20Images%20(orthogonal)/
A common mod to do on the rubber key version is to now directly solder them so that there's space for a heatsink on the ULA as the heat kills them.
@@kurbeco thats interesting... mine wasn't socketed!
Probably would be cheaper to just design a board with sram and some 74xx logic to replace all ram on the computer
There already is at least one board like that around. I'm considering getting one. :)
you need a inline on/off switch badly man for this kinda testing or a reset switch or both even, easy to do inline of the power adapter ? pulling that wire in and out was the bane and demise of a lot of spectrums Psu's as the wires starts to breakdown inside usually right near the jack where the wire enters then when u've finally got your favourite game to load after 50 tries (copies lol) then when u go to reposition your speccy or just slightly nudge it (with your cup of tea/coffee usually) and .......crash argggggghhhhh !!
Yes, I definitely need to make one. I think I have some old light switches laying around, should be easy. :)
Better just to remove a mod board and remove the entire modulator box.