Once, when I was still a foolish teen who wanted to align the RGB electron guns in my Amiga monitor a little better, I managed to discharge it into the inside of my right bicep while reaching across it. It didn't kill me, thank goodness, maybe because the path through the right side of my body to ground didn't really include my heart, but was painful enough that I can still see that moment in time as clearly as someone with photographic memory. I see my old desk, the monitor with the back off, angled to face a bit to my left, and my right arm across it, the open curtains behind it and the clear day outside, etc. Kind of amazing really. Also, I'm not sure if it was visible to others or just the effect of electricity on my nervous system, but there was a very bright white flash. Don't mess with CRTs, kids.
Hi Noel, I worked on CRT test and design back in the 80’s and looking at the schematic I would definitely try cleaning VR703 and VR702, they are right by the video processing chip. I agree the jumping looks a little too regular and interference could be a suspect, but there was so much crud inside and the de-oxit worked well on the three external pot’s so might be worth a try to at least discount that as a potential issue.
interesting comment about the sudden discharge when using a screwdriver. I read on an Apple service manual for an Apple CRT monitor that Apple used to have a discharge tool with a resistor in it which was then replaced by one without one so the technician could have a visual and audible cue on when the tube was getting discharged (the spark and the click noise). Thanks for the video, been missing them!
Hey Noel! Please be careful with these kind of probes! I use them in my job very often. You need to take care your Multimeter has a impedance of 10MOhm so the division of the measured voltage will be right! And the Probe i get shown using your amazon link is the 6kV one. the Cal Test is a 40kV probe that would seem more useable. but the Cal Test and as far as i know the keysight ones are sold out. So any viewer interested in the probe should search for the fluke 80k-40
Good to have a simple one from time to time :) Note that the 12V regulator in these monitors is specified as a 78M12 (rated at 2A) and not the standard 7812 which has a 1A rating. In this sysyem it probably won't make any difference, but if the disk drive is one of those that draws more than 1A it might cause weird issues when accessing disks, particularly when writing data. Great fix though :)
I learnt the hard way about how much voltage a TV or monitor can hold, when taking apart as 14" Amstrad TV as a teen. Got one hell of a jolt, but never again did I mess with the inner workings of a CRT!
Well done for taking the step into CRT repair and not getting fried! If it had been me (and it probably never will) I'd probably have tried to discharge the monitor like 12 times and still worn rubber gloves before touching the anode 🤣 Great to see you using the new lab too, hope it worked well for you, good luck with the next one - and don't get cocky with that HiVoltage! 😋
@@fred-9929 Yeah I bet! *IF* I ever did CRT repair (not in the forseeable) the marigold-gloves wearing for the final step would be mostly for ceremonial and superstitious reasons in my case :)
Have seen people say you should do it to get the spark so you can see that it's discharged... Maybe that'd make sense if you got that spark every single time, but you're not gonna get any if the bleeding circuit works, so just do it properly.
Great video. Beautifully explained. We all enjoy this hobby, but as you point out, safety is paramount. Great to have you back making technical videos again, Noel. Look forward to the colour monitor repair! All the best matey :)
Great video. I have a few monitors I need to work on. I have not seen the HPV-40 until you demonstrated it. There is another purchase I will need for the toolkit!
Awesome video, Noel! For some reason RU-vid wasn't showing me your videos for a while so I had no idea you moved to the land of 110V/60Hz. I'd need to see some pretty high speed slow motion footage to be able to visually confirm it but it definitely looks like an artifact of the 60 Hz -> 50 Hz AC frequency conversion based on some of the artifacts of voltage and frequency droop I've seen working on sensitive networking equipment in power plants here in Canada. Keep up the awesome work!
Nice vidéo as always. The 12v Reg for the floppy is normally a 78M12 a 0.5 amps model and not not a regular 1 amp. Usually these regulators are very well protected and to blow it as violently as it did it must have been it mut have got some voltage fed to the output. To fix the vertical jitter there are a few possibilities: - Jitter in the supply voltage - Oxidized potentiometer Put an oscilloscope between pin 1 and ground, check if you can see jitter in the signal: If no, the jitter is not produced by the vertical circuit -> other source like interferences etc... If yes, then try to clean (de-oxit) VR701 and VR702 (vertical size and position) If the problem persists check the supply voltage with the oscilloscope to see if it jitters too. If no, then the instability may come from the vertical oscillator (capacitor, vertical hold etc...) If yes, then the jitter can come from the power supply itself or anywhere in the circuit back to line voltage If the problem comes from line voltage (insufficient line regulation) try moving the monitor and computer to a completely different circuit and see if the problem disappears. I have seen similar problems in shops were they had 20 or 30 CRTs on the same circuit. The only very imperfect solution is to use AC line filters but that's a real pain and it never really works 100% As a last resort, changing the power supply to a switched 12v is a possibility by then the switching frequency might become visible unless you use separate DC to DC converters. I hope that helps.
Hey Noel. The jitter is probably beat interference from the mains 60Hz and the vertical refresh at 50Hz. It can happen the other way around too, when a US computer is used in Europe. Here's what I did to tackle it in a PET 2001: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-w44i-WKJxV8.html
Very interesting! I'll definitely have to have a look at the sync signal on the monitor board to see if I get any of that interference like you did. Thanks!
Hey Noel, I suspect that the jitter is due to increased magnetic flux from the mains transformer. Its positioned in the case at 45 degrees to eliminate it. Maybe this angle is not sufficient at 60Hz? Like Adrian said a DC conversion would help. You could try as an experiment extending the 4 DC wires from the transformer and moving that away. It might be enough to just run the monitor with the cover removed. I Meanwell power supply would be a great upgrade. Not only would you eliminate that stray magnetic flux but it would be multi voltage and you could eliminate the need for that step up transformer.
Another interesting look at Amstrad hardware - thanks! It might be interesting to get the O-scope on the power and see if there is a really large amount of ripple or harmonic noise.
As my Dad would say: "If I touch the brightness dial, I get a lot of interference" ... "Then don't touch the brightness dial" ... 🤔. Seriously though, very handy video to keep saved - I've got a Commodore PET with a brightness issue that I need to fix but have been reluctant to go sticking my hands in there whilst powered on ... but how else can you trouble shoot? ;) /Brett
As RL showed, you don't need to troubleshoot, be powered on, or even plugged in. Just squirt some Deoxit into the variable resistors ("potentiometers") that are behind the brightness dial. Rotate them back and forth all the way a few times. Let it dry for fifteen minutes or so and you should be good to go.
I love my Amstrad CPCs, having had a 464 and 6128. I’ve never found any in the States, where I now live, so I had to buy a 464 when I was visiting home, and bring it back in a suitcase. I hope to find a 6128 sometime and bring that back too - but clearly no monitors for me! I use an RGBtoHDMI adaptor, and it’s a fantastic image. I do miss my green screen CRTs (a little) 🙂
5:11 in fact your left hand should be inside your rear pocket so in the event a strong current DO passes thru your body (when you touch the anode with your right hand using the probe, assuming it conducts current against all odds) a part of that current goest thru your left arm "in parallel" with some current passing thru your upper body where your heart can be critically hit (it's best to lose sensitivy in your arm than to have a heart attack right?). Also NEVER NEVER WORK ALONE IN THESE ELECTRICAL SHOCK RISK SITUATIONS! (i.e. a coworker or relative can save your life if he/she is ready to turn power off or use some isolating material, like a wooden pole or stick, to stop you from connecting with equipment)
Great job Noel, did you find the remains of that broken voltage regulator inside the monitor case? As always, I loved watching and your "walk" looked like you have the perfect natural environment for such things, very cool!!! Best wishes, Michael
I didn't! So that must have happened before I got that monitor (and somehow I never tested that PSU). And yes, there's some wonderful nature right around here.
Ese Jitter me recuerda a mi super nintendo con la panasonic panablack de 29" conectado por rgb, sin embargo en las otras televisiones la imagen es perfectamente estatica. El problema al menos no era de la consola pero si del monitor y solo con esa consola. Es muy raro. Muchas gracias por este video, saludos.
@@NoelsRetroLab I haven't done measurements with oscilloscope myself, but I recently put one in my Macintosh Plus, and the CRT is rock solid. They are designed for modern computers, so I guess it shouldn't be too bad. Would be interesting to find out though!
The reason why you see the jutter is most likely the fact that you use the transformer with 60Hz while the monitor itself refreshed with 50 Hz. So you see a 10Hz wobble from the transformer interfering with the crt beam.
It's probably the magnetic field from the transformer inside the monitor. When operated on 50 Hz it would only be moving very slowly with respect to the frame flyback, but when operated on 60 Hz you get a beat frequency.
@@NoelsRetroLab You would need to put a magnetic shield around the transformer. It would be easier to convert the monitor to use a switchmode power supply in place of the linear one.
As for the DC idea, it should work if the chassis all runs off DC, just have to get the input volts right as well as the power ratings of the DC supply, I'm in the midst of sticking a C64 DTV board inside an old 6" portable TV (which is a triple-play power setup, battery, 12vDC & mains 240v) and have ditched the old inefficient linear power supply in favour of a slightly over-rated Mean Well 12v 50w PSU in its' place, as it may eventually also power other stuff inside depending on how the project goes... :)
i just finished watching retro recipies latest video about the 80's theyre having issues with a tv/monitor from the uk i believe the issue you have with your monitor is the same as his issue. your voltage transformer thing can produce the higher voltage but it doesnt change the Hz so that is probably the same issue for you. im sure there is probably some solution to it though
I suppose the internal transformer may interfere with the CRT. Switching PSU would be a solution, it completely isolates the electronics from mains frequency.
The capacitors may physically look good, but could have dried out over the years internally resulting in them not smoothing out the signals as they should, worth popping them out and testing them out of circuit to be 100% sure... :)
I have a ctm644 that I had not used in a long time and was running the boulder dash demo on, a short time later the monitor died and I have been to nervous to even attempt a repair on it
I would suggest, VERY carefully. As a child I was always taking things apart for, well, parts. The number of times I was knocked about by a CRT is not funny, but then again I was around 8 years old... lol.
I have a Microvetic CUB monitor for my BBC micro and it also has this jitter, little more pronounced. It’s really irritating and would love to get to the cause of it
Since 120 Hz is _higher_ than 100 Hz, I doubt that the choice of filter capacitors is an issue. They may have dried out or become DC leaky over time though, even without visible damage.
Hello! I've tried to search the internet, but no meaningful results are coming up. I have a color CRT monitor, LG Flatron F700P to be precise, and there is color fringing in it, or at least that's what I believe it is. Basically, ghost-like images to the right of everything. What is the way to fix it? I heard it's possible color beams need to be calibrated, and I would need to open up the monitor for that and likely have it *on* to adjust it so that I can see everything, and I'd rather avoid that if at all possible.
I'm not sure I would call Adrian black an expert on monitors, he seems more like a replace things until it works kind of guy to me. He does far better with the computers themselves. That's not too say i know better, but i know enough to recognize shortcuts. Just replacing the transformer is an example of a big shortcut. It should be possible to actually fix the problem.
Hi mate, can you send me an Amstrad T shirt ? XD PS. Quite common for those 7812’s to go pop. Replaced a couple again the other day while on my repair frenzy 🤦♂️
I have a panasonic crt tv and it's board blew multiple regulators and I replaced them all and yet it just blew its fuse again. Very frustrating trying to fix crts
The problem with High Voltage Probes is they're over $300 USD! Is there a more cost effective solution? Could you make a discharger using a high resistance device, like an incandescent light bulb?
Yes, you can make a CRT Discharge Tool for a *lot* less; in fact you probably have the parts laying around. There are instructions on how to make one on page 11 of the book Macintosh Repair and Upgrade Secrets by Larry Pina (1990). You need an insulated test probe (like from a multimeter), an alligator clip lead, and a 10M resistor. (I'm presuming you have a soldering iron, wire, and heat shrink tubing already). Here are the instructions from the book: An easy-to-make custom discharge tool is shown in place, in Figure 1-15. This tool is made from an insulated test probe, a green clip lead, and a 10-megohm 1 /4-watt resistor. To make your own tool, cut off one end of a green clip lead, unscrew the test probe handle, slip the handle over the wire, and cut the resistor leads to size. When you screw the handle back on, the resistor leads should be completely insulated by the test probe. There can't be any exposed metal. Readjust the leads as necessary, then solder everything together. For safety, cover the entire tool with heat shrink tubing. Never unscrew the handle while the tool is in use!
The yellow # on back is probably a service tag for a school or business. The fact you are having trouble removing it actually makes sense if it was a school computer. You don't want kids removing a service tag.
Yes, unfortunately it's very expensive. I bought this one off Ebay for about $100, so what you're quoting seems extra high. Heck, you could buy it from the US and ship it and be way cheaper than that. But maybe things have gotten more expensive for some reason.
It's a decent hypothesis. Doing that shorts both rails to ground (the 12v socket is centre negative), and while the 5v supply has a protection circuit and cuts out safely, the 12v is just the 7812 and would have a bad time (luckily it's cheap and readily available)
Yeah, that makes sense. I guess Amstrad should have gone with a smaller diameter DC jack on the 12V PSU to prevent that but they went the cheap route 😃
Never work or open unless you know how to discharge the tube and any large capacitors also double check it is unplugged do not think it is safe by switching it off also use one hand at a time when finally reaching in and take care of any sharp items inside
Ah interesting! I knew they had their own TV brands, so it's interesting that they would in turn sell just the tubes to Amstrad. But I guess that makes sense.
I can't tell you if it's OK, but I can definitely tell you if it's bad 😃 I'm alway suspect of an in-board LCR check and this wasn't supposed to be an in-depth check (because I also don't suspect the capacitors in the first place).
PaulT - As Noel says it was just a quick look whilst it was in bits. A bulging capacitor is a thing but you may have not experienced it yet in your learning journey but does not mean it does not exist.
Speaking of safety, here's a cool trick I saw the other day - put a piece of heat shrink tubing over the end of the pins inside power plugs so you can probe them without worrying about accidentally shorting something. (I suppose you could slip one up over the multimeter probe too.) ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ZXH-L2GOH94.html
