Macintosh Plus power supply troubleshooting and repair

Рет қаралды 73,274

Жыл бұрын

#apple #macintosh
On today's video, I'm going outside my comfort zone and working on analog stuff. It's a very broken Macintosh 128/512/Plus power supply/analog board. It was sent in by Tommy of the KZfaq channel Arctic Retro as a broken part. He didn't know what was wrong with it other than the machine wouldn't power on. So let's find the faults with this board and get it working again!
--- Video Links
Tommy's channel Arctic Retro:
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Thread on replacing the variable potentiometer with a modern part: (Thanks to patron Flying Toaster)
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Adrian's Digital Basement Merch store:
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Deoxit D5:
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Elenco Electronics LP-560 Logic Probe:
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Hakko FR301 Desoldering Iron:
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TL866II Plus Chip Tester and EPROM programmer: (The MiniPro)
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EEVBlog 121GW Multimeter:
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DSLogic Basic Logic Analyzer:
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Magnetic Screw Holder:
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Universal ZIP sockets: (clones, used on my ZIF-64 test machine)
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RetroTink 2X Upconverter: (to hook up something like a C64 to HDMI)
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Heat Sinks:
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Little squeezy bottles: (available elsewhere too)
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--- Links
My GitHub repository:
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--- Instructional videos
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--- Music
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Пікірлер: 253

@dennissdigitaldump8619 Жыл бұрын

Even at Apple we called that the devil board. So many CRT's & motherboards were killed by it. I was with Apple way after, these machines, but they came in for repairs. Even some of the New Old Stock boards were wonky & I was a rare soldering tech at Apple. So I saw about 50 or so

@TheMechanator Жыл бұрын

Can confirm it can be devil to troubleshoot. I had to hand these boards off to the master analog repair shop manager sometimes to shorten the troubleshooting time. I eventually got into the groove with several brands of monitors. The damn things are proof of "spooky interaction at a distance" when you get incoming RF and magnetic fields affecting the picture.

@megadjc192 Жыл бұрын

Oh, I can tell you why it tripped the breaker. Your step up transformer is wired in split phase. European power is single phase 240. So in Europe neutral is at ground potential. Your step up transformer is neutral at 120v with respect to ground. This isn't safe and you should not run that step up with that configuration as you can short 120v directly to ground if you have a neutral bonded to ground in a chassis for some reason. Don't use that step up transformer for anything. You need a proper one that keeps neutral at ground potential and the hot needs to be 240v. This is why your circuit breaker tripped. (edit: since the tranformer probably has split phase output you just need to rewire it correctly so the center tap isn't connected to your ground, but remains capped off and disconnected.)

@tommyovesen Жыл бұрын

Thanks for featuring my board. I knew you could figure it out. Great work!

@jeromewhelan6723 Жыл бұрын

I just developed a great big smile when I saw you using the mirror to look at the screen while tinkering with the set electronics! That brought back so many memories from 53 years ago, as I was a bench tech at Bernie's Radio & TV.

@kpanic23 Жыл бұрын

In case anyone wonders how these dual supply voltage switch mode power supplies work: They're basically 220-240V power supplies, only the big charge capacitor on the primary side is replaced with two capacitors in series. On 230V everything works as normal, the mains AC is rectified and goes to the capacitors. If you switch the power supply to 120V (either with an external switch or, like in this case, with a wire link), the center point of the two capacitors gets connected directly to the AC supply, before the rectifier. That way you turn the full bridge rectifier into two half-wave rectifiers, basically creating a voltage doubler circuit: the positive half wave of the input AC charges one capacitor with a positive voltage, the negative half wave charges the other one with a negative voltage (referenced to the center point). That way you get two capacitors charged to roughly 170VDC, which in series is equal to the roughly 340VDC you would get when rectifying 230VAC. It's simple, elegant and quite ingenious!

@viperwizard491 Жыл бұрын

voltage multiplier circuit for 100V and 230V as regular rectifier switched with one jumper link

@seancurtin6103 Жыл бұрын

I always wondered how they did that! I just figured it involved a center tap on the primary of the transformer or something.

@nickwallette6201 Жыл бұрын

@@seancurtin6103 I would have thought so, too. The PF on that circuit can't be too great, since you would have to go with a passive PFC coil, and optimize it for either voltage setting, or the midpoint between them. (I think.)

@steeviebops Жыл бұрын

@@nickwallette6201 Any ATX PSU that I've seen with a voltage toggle is passive PFC.

@tw11tube Жыл бұрын

@@steeviebops Active PFC circuits usually are step-up converters that step the momentary rectified mains voltage up to 350V to 400V, doing so with a good power factor. The regulation range of the active PFC circuit is wide enough that it can cope with 90V-240V input without any circuit modifications. That's why you don't find that toggle switch on active PFC supplies.

@Breakfast_of_Champions Жыл бұрын

Pretty advanced and even a bit scary - you're a great technician Adrian.

@williamsquires3070 Жыл бұрын

Ha Adrian. You can test that SCR with your meter in continuity/diode-check mode. Put the black wire to the cathode of the SCR, and the red lead to the anode of the SCR with the gate floating. You should get an open circuit. Now, briefly connect the gate to the anode. You should get continuity (or a few volts drop) and it should stay that way until you disconnect it, wherein it’ll go back to being an open. For low-power applications, you can replace an SCR with a 2N3904 & 2N3906 (i.e. one NPN & one PNP). The emitter of the NPN is the cathode of the SCR. Wire the base of the NPN to the collector of the PNP, and bring this out as the gate. Wire the collector of the NPN to the base of the PNP, and the emitter of the PNP now becomes the anode of the SCR. Theory of operation: initially, both transistors are off (SCR not conducting.) When you pull the gate positive w/respect to the cathode, the NPN transistor conducts, bringing it’s collector close to ground. This turns on the PNP transistor, which now conducts, bringing it’s collector to the voltage at its emitter. This keeps the NPN transistor on so the gate signal can be removed and it will still conduct until the circuit is broken (no more current.) Finally, this mock-up of an SCR is just for testing; use a real SCR in the circuit!

@Clavichordist Жыл бұрын

This was a great troubleshooting video. I really enjoy these. You may find this helpful. Going back into my memory from my tech days, square pads on the circuit boards indicate the positive pin for electrolytic capacitors and the direction for other directional components such as diodes. For ICs, the square pad is for pin no. 1. This makes troubleshooting a lot easier.

@Stoney3K Жыл бұрын

It may be a good idea to wire that step-up transformer to have a CEE7/7 (Schuko, or type E/F universal) socket, so you don't accidentally plug in a 115V device into the 230V part of the transformer. Schuko to IEC power cables can be found practically everywhere.

@williamsquires3070 Жыл бұрын

(@51:05) “None of those (capacitors) needed to be changed.” Except the infamous RIFA cap! 😂

@frothysalsa Жыл бұрын

A step-up transformer is a transformer that takes on extra responsibility for the good of the team. ;)

@steves009 Жыл бұрын

And 240v is more common in the world than 110v

@AndrewTubbiolo Жыл бұрын

@@steves009 Saves copper. The US standard of 100 goes back 100+ years ago. Since we started early our standards meet older needs.

@JoelReesonmars Жыл бұрын

笑っちゃう

@Loki- Жыл бұрын

It's not my real transformer. It's my step-transformer.

@Doug_in_NC Жыл бұрын

@@AndrewTubbiolo The US ended up with roughy 110V because light bulbs in the 1880s could only handle that. Europe’s systems started being built out a decade later by which time bulbs that could deal with ~220 V had been developed.

@retrobitstv Жыл бұрын

Another masterclass in diagnosing compound faults. Awesome repair!

@russellhltn1396 Жыл бұрын

27:16 I think you need to look at how your step-up transformer is wired. It appears the switch does kill the power (line - neutral), but it's leaving 120V from line (or neutral) to ground. That could give you a nasty surprise in the future.

@fumthings Жыл бұрын

cheap ones are usually an autotransformer, for safety use an isolated step up transformer.

@russellhltn1396 Жыл бұрын

@@fumthings It's not the isolation I'm concerned about. It appears the power switch on the unit opens the neutral and not the hot, leaving line power on the output. Although, maybe the problem is the power plug it's plugged into isn't wired right.

@fumthings Жыл бұрын

@@russellhltn1396 ok, understood.

@garthhowe297 Жыл бұрын

It is hard to top your previous troubleshooting videos, but you still manage to create an even better one. Thank you for these videos.

@CATech1138 Жыл бұрын

for my .02 any diag vid by this guy is on my top 3 must watch now list.....

@Peter_S_ Жыл бұрын

I remember getting those red battery holder with black silkscreen analog boards as service parts in about 1991. My guess is Apple decided to standardize on a single repair part that late in the original Mac life cycle. It's funny what gets stored in your brain.... I remember a note in the package about making sure the W12 jumper was set up correctly for the voltage it going to be used with. Being a service tech in those days was a different experience.

@nilswegner2881 Жыл бұрын

Nowadays a service techs only job is to tell people how stupid a repair is and sell them a replacement

@lemonmerrengue Жыл бұрын

You inspired me to recap my sad MacPlus board after your video last week and it is working now. Thanks for cool videos!

@Peter_S_ Жыл бұрын

Congratulations! 👍

@MrDeelightful Жыл бұрын

It's a great day when I see a video from you Adrian! You have a very good way of visually explaining things, your videos are always top-notch. Love from just north of you in BC :D

@Dukefazon Жыл бұрын

I like your dedication to fight against mindless recapping :)

@billfruge25 Жыл бұрын

Absolutely love your diagnostic repair videos. Have learned so much about the methodology and reasons behind why it's so important to learn and know how different components behave and interact.

@mickholling6819 Жыл бұрын

Great video as always Adrian. I used to do a fair bit of board repair with 2 years straight just working on CRT's. Watching your video's brings it all back. Superb. Keep em coming. EDIT: The NEC Multisync monitors I think were the most difficult patients of them all for me. That one used to come in with some very random faults. And the harder they are the more fun they are.

@adriansdigitalbasement Жыл бұрын

I remember reading that those monitors are also quite complicated with a bunch of boards inside -- making troubleshooting that much harder? I've never had to work on any luckily!

@mickholling6819 Жыл бұрын

@@adriansdigitalbasement Indeed. Shango66 had one on his channel.

@jjock3239 11 ай бұрын

A very enjoyable video. I enjoy watching your analytical skills in action.

@nobuckle40 Жыл бұрын

Nice! Love watching you troubleshoot. I always learn so much. Thanks.

@GarthBeagle Жыл бұрын

Damn good job, lots of danger and new experiments/repairs with this one 🤘 And finally, something that actually had a failure (failures!) instead of it just fixing itself

@ChrisHalden007 Жыл бұрын

I am so impressed by all those diagnosis videos. Still stuck with my own analog board repair for months 😂 Great video. Thanks

@ronostrenski8359 Жыл бұрын

Short circuits are easy. Use your bench power supply and inject 5V. Limit current so not to burn tracks and the offending component will warm up. If you have a thermal camera, it’s even quicker. Great work with finding the faults. Regards Ron

@JamsterJules Жыл бұрын

Great video as usual. I really enjoy watching you troubleshooting these issues. Can't help flinching when your hands go near the HV! (I know you know what your doing!)

@JimAlfredson Жыл бұрын

Your troubleshooting videos have taught me so much. This is another great one. Thank you.

@GonogoBonobo Жыл бұрын

Concerning SCR testing with a multimeter, normally Gate-cathode junction act like a diode. But anode-cathode should be open both direction.

@MrAsBBB Жыл бұрын

Loved every minute of this! All the best from the UK

@bwack Жыл бұрын

You have good analytic skills, and the fault finding was exciting to watch! Also nice to see a board from Tommy :D

@colepdx187 Жыл бұрын

My favorite part of Saturday mornings :) Nostalgia and edification

@williamsquires3070 Жыл бұрын

Oh, I thought it was nostalgia and petrifaction. 🤔

@colepdx187 Жыл бұрын

@@williamsquires3070 It is of course subjective. I can only speak for myself. 😎

@michaelhaardt5988 Жыл бұрын

Great analog troubleshooting, I learned something today.

@KurtSchefter Жыл бұрын

Man, vids like this are sooo satisfying... Thanx Adrian!

@gmirwin Жыл бұрын

23:42 That's a needlessly complex turn signal for your car! 🤣

@argvminusone 7 ай бұрын

I've seen some actual cars with fancy animated turn signals, presumably controlled by a computer. Wouldn't be surprised if that computer is faster than this Mac.

@jimfischer4703 Жыл бұрын

Amazed! You have a gift my man.

@DavidStahlOLDHAPPyMACs Жыл бұрын

Great Fix Adrian Good Approach. The Repair

@Emiko1 Жыл бұрын

45:19 Discord notifications, thought it was mine

@LymanGreen Жыл бұрын

Nothing can make me nostalgic for old Macs like a great diagnostic/fixit video.

@eliotrulez Жыл бұрын

nicely done!

@Colin_Ames Жыл бұрын

Excellent detective work!

@haraldweinreich9522 Жыл бұрын

Another great Video, thank you so much. You just scared my quite a bit when you touched the hi-voltage part of the switching power supply with your hands. Maybe show us how you discharge that part of the power supply and make sure it is fully discharged, too? Greetings from Germany!

@georgegonzalez2476 Жыл бұрын

That SCR was part of a power supply crowbar circuit, just in case the 5 volt supply went too high. So not absolutely needed but maybe so if someone went and tweaked the voltage too high.

@adriansdigitalbasement Жыл бұрын

Ah yes! I would have to think with that crowbar design that it should have been able to handle the over voltage without failing short?

@georgegonzalez2476 Жыл бұрын

@@adriansdigitalbasement I could have lost an eye once when a crowbar circuit tripped and a 1 ohm 1 Watt resistor in series with the SCR exploded. The only problem I've seen with the Mac analog board is the vertical yoke capacitor. It handles several amps of current and tends to go bad or heats up its terminals and unsolders itself. You can see premonitions of this if the vertical height of the screen jumps around a little bit.

@tw11tube Жыл бұрын

@@adriansdigitalbasement These crowbar circuits are designed to actively short the rail that overvolts. Because they short that rail, the voltage across the SCR is "not that high", so the amount of power dissipated by the SCR is limited. Yet, an triggered SCR still has some forward voltage (IIRC, around 1.5V), and a broken supply putting several amps into it will dissipate some more several watts in the SCR. Crowbar circuits are not meant to operate continuously, but it is expected that the supply breaks down (blows a fuse, activates short-circuit protection) within some time. If that doesn't happen, the user is expected to power off / unplug the device. As you see no heatsink on the SCR, it may overheat if left in shorting mode for too long. The typical failure mode of overheating power semiconductors is going short. That's likely what happened on your supply, as the +5V setting was tuned too high, so the crowbar did it's job, sacrificing itself. The crowbar circuit *still* *seems* *broken*. You shouldn't be able to get 5.8V out of that supply without the crowbar triggering. At the moment when you got 6.3V, the regulation and the crowbar was not connected, so it didn't have a chance to kick in. For continued protection, please check the crowbar operation, you might have a broken component in the SCR drive circuit.

@jimperry6463 Жыл бұрын

This was quite the adventure. Thanks.

@Dinnye01 Жыл бұрын

The cherry on the top of a Saturday!

@AmstradExin Жыл бұрын

Adrian is a heat seeking missile towards the weirdest problems.

@randyab9go188 Жыл бұрын

Adrian get a ESR meter. As much as you work on older electronics you really need a good one. EDS-88A CapAnalyzer Series II Electronic Design Specialists Cap Analyzer I can wholeheartly recommend. I own and use that one and a Capacitor Wizard Analog ESR Tester with charged capacitor protection board added. The digital unit (EDS-88A) will perform a short circuit test before the esr test as a short circuit can simulate low ESR. The cap wizard does not have this capability. But both are excellent testers and the results are accurate. Also when I have a power supply that has not been on in a long time, I will put the dim bulb tester in series and bring up the power supply slowly (unloaded) with a variac. I feel it has definitely saved me from exploding electrolytic capacitors. It will do nothing for the rifa cap issue so snip those out before starting!! I had a GME Professional In-Circuit ESR Capacitance Meter Capacitor Tester for a while and sent it back. It had quality issues and would lock up if testing caps in rapid succession. Do not recommend. Price was nice but no comparison to the other units mentioned above!!

@eDoc2020 Жыл бұрын

Another benefit is the ESR tester uses high frequency so inductors look open instead of short. This helps you determine if a short is "real" or not.

@danriches7328 Жыл бұрын

Most 5v chips from that era can handle 7v absolute max before the magic smoke is permanently allowed to escape, I've certainly done exactly the same before with no ill effects. Thank goodness the error margins for overvolting are quite large. Nicely repaired Adrian, also Deoxit to the rescue again ;)

@bjn714 Жыл бұрын

51:00 we will just forget about that RIFA, even though it was probably bad and mere moments from releasing the wonderful fish-scented perfume they're known for anyway, despite not being the source of the breaker tripping. I know you were referring to the electrolytic you removed and replaced, but you did also remove the RIFA, which was necessary anyhow.

@adriansdigitalbasement Жыл бұрын

Haha yeah I just left it off entirely --- they just do filtering so really it's only needed for EMI anyway :-)

@BensSightSoundandAuto Жыл бұрын

Hi Adrian, I have one of those component testers, and I found even not being used it would go flat fairly quick. I added a switch in the positive line between the battery and the PCB to isolate it when not being used. Otherwise its a great tool! Love your videos mate, from Sydney, Australia.

@tommythorn Жыл бұрын

good detective work - I don’t think I would have know where to start

@bakutools Жыл бұрын

Cool, brings back to life

@Cherijo78 Жыл бұрын

41:43 clearly that dead RIFA cap is still good for something. 😂

@Agent24Electronics Жыл бұрын

The only thing it's good for :P

@Ingineerix Жыл бұрын

@Adrian, the SCR is a "crowbar" circuit that's used to protect the power supply rail from excessive voltage. Sometimes if they do overvolt, the SCR can fail shorted. SCRs operate like diodes, but they have "trigger" input (gate) that once is powered the diode part begins conducting and latches on as long as there is a certain threshold of current flowing. This makes it a perfect choice for the latching function of the crowbar. It literally shorts out the rail if it's trigger circuit detects an overvolt on the rail (usually a zener circuit).

@m1geo Жыл бұрын

Those pots are super common.

@ITGuyinaction Жыл бұрын

👍 👍 👍 Well done! I also like repairs of old electronic equipment...

@twocvbloke Жыл бұрын

It's so much fun getting a CRT to fire up and show a picture after going through all that work to find one small and annoying part that died... :P

@alanbenson1505 Жыл бұрын

You should look into a Peak DCA55 component tester for those ICs. They do a more advanced DCA75 version, too. I've had a DCA55 for a while now, I love it!!

@vk3hau Жыл бұрын

45:35 , when you put the Prob on the video Signal pin from the motherboard is when the Picture appeared on the screen, the fault is on that pin, not the connector going to the neck connector on the crt.

@zitt Жыл бұрын

Exactly. Review the video Adrian. :D

@nicholaslewis7208 Жыл бұрын

Yeah new Vid!!

@MrUSFT Жыл бұрын

Arctic retro!! What a great channel!

@darrenbeeken8648 7 ай бұрын

Excellent repair mate, just one thing. But!!!But!!! you need to replace all the caps😅😅😅

@Fifury161 Жыл бұрын

It's always best to work on CRTs standing up and with a clear path - that way if you do manage to get a shock you'll have an easier time removing yourself from the situation!

@hgbugalou Жыл бұрын

One hand rule is one I like to follow when dealing with a sketchy situation like that. It'll hurt like hell still but won't stop your heart!

@stevethepocket Жыл бұрын

I feel like if I ever started servicing picture tubes or other high-voltage equipment, I'd just get some really heavy rubber gloves. I've never understood why that's not a normal thing to do.

@kaitlyn__L Жыл бұрын

@@stevethepocket good luck using a soldering iron through those extra thick Marigolds ;)

@TheMechanator Жыл бұрын

@@hgbugalou Yep, one bit me once, and I lived to talk about it. I was one handed and standing. What I didn't expect was my elbow being pushed by a curious tech next to me when he leaned over. From that point on, I told everyone when I was servicing monitors to stay away unless invited. The shop jokes about my hair standing up and smelling cooked hot dogs went on for a few days.(groan)

@MattPlachecki Жыл бұрын

30:00 Mad scientist vibes ⚡️

@YugoZex Жыл бұрын

I remember when I was kid in 80's people smacked tv a lot when they loose pic. I know now that that is usually bad soldering joint due to heating and cooling all the time but people had a myth that tv is fixed if you smack it.

@andrewchristiansen8311 Жыл бұрын

30:13 12,000 volts scares the crap outta me. My palms sweat when you touch the yoke or any part of the CRT cause I dont understand what part kills you or when. You're brave I'm not touching that stuff.

@InssiAjaton Жыл бұрын

A few comments --- 1) Your house has 240 V for a range ot something else, if you just dig it out. Your 120 V is duplicate in voltage, but just one half of the 240 V each, because it is a center tapped arrangement, with the tap grounded. 2) Your step-up transformer is not isolated between primary and "secondary" - it is another center tapped gizmo, just like a Variac, only not adjustable. That explains the ground fault trip until you added the isolation transformer in front. 3) I like to use a Diode Test mode on the DMM when checking semiconductors instead of plain ohms. The diode mode typically drives the circuit with a 1 mA current and displays the developed voltage "drop" in direct reading. That tells the 0.6 or so voltage of small silicon junctions. More on Darlingtons and less on Schottky. 4) Switching power supplies I like to start analyzing with a pair of field probes ( magnetic field or electric field ), attached to my oscilloscope. 5) Inductive, as well as capacitive components I usually can measure with my DER 5000 meter, using its 100, 120, 1k, 10 and 100kHz frequencies and a little reasoning. The IMPEDANCE of both inductances and capacitances varies by the frequency, but possibly parallel connected resistors don't vary. 6) When dealing with unknown way grounded systems, I have some tricks in addition to an isolation transformer. I have battery operated differential probes and even a Tektronix dual channel probe isolator device. But often I can use a Tektronix current probe. I have two, one small, 10 or 20 A maximum at 50 MHz and a big one up to 500 A and up to 2 MHz. Finally, 7) I have an old HP probe set that consist of a pulser, a logic probe and a pulse current tracing probe. Works great, as long as I can avoid the apparent short circuits that any capacitors show on the fast pulses. . I hope this gives another view to means and instruments that can be used for troubleshooting unknown devices.

@danielmantione Жыл бұрын

Interresting that you did all the troubleshooting on 240V. If I troubleshoot power supplies, I always use my isolation transformer to generate 115V for safety reasons. The transformer itself adds a lot of satety, the reduction to 115V makes it even more safe. Typically a power supply like this runs on 115V, there is usually no need to switch it into 115V mode. The amount of power it is able to generate is greatly reduced and there is good chance it won't be able to drive the computer unless you reconfigure it to 115V. However, to check wether it is generating the right voltages, the low voltage is often sufficient. When all faults are removed, I plug it into the 230V output of my isolation transformer and then test it at full capacity. Usually I connect a few halogen lamps and let it run for an hour or so. Only when it passes such a test, I am willing to let it power a computer.

@tom940 Жыл бұрын

i've got a tough mac plus thats been one of my on again off again projects, recapped the power board and fixed some cracked solder the usual culprits, had some trouble with the ram slots and there were a few traces that didnt appear to be connected anymore, bad ram sticks, one of the rom chips was bad and its still not quite booting. Im pretty sure ive got a few more traces to check on the logic board but the schematics for that are hand drawn and missing some pieces between where they were scanned in many years ago, i started to try and piece them into one sheet with an image editing program but it only got me so far

@petesapwell Жыл бұрын

Good work Adrian :)

@petesapwell Жыл бұрын

There was an inductor in series on the missing supply, with the diode looking short removing one leg of the inductor narrows down the possibilities, my first suspects are Always secondary diodes never caps.

@TheMechanator Жыл бұрын

Still, at 15:10 the capacitor he pulled should have been checked with a meter for high resistance going down to know that it wasn't shorted. He discounts it as probably good and decides to put it back in. Might as well quick test it before putting it back in. Also LCR meters are cheap sub $50 devices now to know the value of the cap hasn't changed drastically. If it works, who cares about the ESR value as this is a 60 hz power supply thing. That would also help in chasing multiple part failures causing a section of circuits looking like it's all shorted. :}

@DarrenHughes-Hybrid Жыл бұрын

Funny: You took the Rifa Cap of the Board @ 26:48 and @ 41:42, put the Board on the Rifa Cap! LOL 😀

@Eytaris Жыл бұрын

Thanks for the video Adrian, good as always! If I may suggest, you should invest in a face shield designed for electrical works, safety goggles sadly aren't enough for two reasons: first, goggles will protect your eyes against incandescent flying debris, but not the rest of your face, burning pieces of metal, plastic and electrolytes will bury very deep into the skin, to the bone in fact and sometimes deeper, causing irreparable damages to nerves, muscles, etc... that can be lethal, if you are unlucky. Second, the flash can burn your flesh and retinas, even wearing goggles, the UV light is so intense, comparable to arc welding and maybe more, that simple goggles wont protect you. electrical face shields have UV filters capable to withstand a flash, at most you may have a temporary bright dot in your vision and maybe a light sunburn on the cheeks, but that's rarely the case. you can add to that a pair of electrical gloves if you need to approach live circuits and a closed long sleeved vest, preferably without metallic buttons (for obvious reasons), made in cotton (synthetic fibers will melt and stick to the skin, cotton wont) and a high collar (to protect you throat). I don't know what the electrical protection ratings are in the US, I'm in France, you might need to do a bit of research, still, electricity is the same either side of the pond, it's dangerous and it can kill but can do wonderful things if properly handled ;).

@Bianchi77 Жыл бұрын

Nice video, thanks :)

@josbouten Жыл бұрын

Nice video! Trying to find the cause of a short using a multimeter is difficult. You tend to measure low resistance values everywhere without finding the actual short. Using a simple current source and your rmultimeter as described by the youtube channel Learning Electronics Repair's video "Convert Your MULTIMETER into an accurate SHORT CIRCUIT TRACER Finder" makes this much easier. It might be worth your while to look into this.

@orion310591RS Жыл бұрын

18:43 - I believe that Igt is reason why this component wasnt read properly. TC1 states it can measure Thyristor / Triac IGT < 6 mA, and data sheet for 2N6395 says typical Igt is 5mA, so its on limit. I believe that TC1 is weak and cannot trigger Thyristor gate. Edit: Known errors and unsolved problems: 5. The output current of the tester is 6MA/voltage

@adamm2634 Жыл бұрын

I suggested a dim bulb current limiter in the past, but in this case you would need a ~220v compatible one! I wonder if building a dual voltage model would be feasible...

@randyab9go188 Жыл бұрын

Look up dim bulb tester for troubleshooting electronics. You insert this in series with the power supply with an appropriate wattage incandescent light bulb. If there is a catastrophic short or if the power supply is drawing too much current the light bulb will limit it to a safe value and you will tend not to blow things up. Super easy to construct. All you need is an AC socket and AC plug a lamp socket and a light bulb. If you want to get real fancy you can install a switch to bypass the light bulb. People who troubleshoot switching power supplies for a living always use something like this.

@eDoc2020 Жыл бұрын

I think he has one.

@CrazyMan_Engineer Жыл бұрын

I noticed that each of the bigger blue caps have a peace symbol as the pressure release.

@johnathon9056 Жыл бұрын

You do have 240V in your home if you live in the US, its just not present at the outlet, all of your high energy appliances such as Central AC, Stove, and Clothes Washer/Dryer run on 240V, we have Split Phase power in North america.

@ironcito1101 Жыл бұрын

23:42 Power on, yellow light starts flashing, "OK, so it's turning" 😅

@ToomsDotDk Жыл бұрын

for the SCR maybe look at the Peak atlas SCR100 Atlas SCR Thyristor and Triac Analyser I got an number of there small tester and they work great

@iblesbosuok Жыл бұрын

Crowbar thyristor. You should test zener which drives crowbar thyristor.

@darrenmurphy6251 Жыл бұрын

thyristors in computers are usually only there as a overvoltage crowbar ,so imagine my horror when you were about to power up the logic board @19:35 without looking into why that scr went short or what it does! thanks for not supporting the badcaps myth!

@makomk Жыл бұрын

SCRs used to be quite common in CRT drive circuitry back in the day, I think, probably because there were limited options for high-power semiconductor switches.

@darrenmurphy6251 Жыл бұрын

@@makomkyes that was mostly sony trinitron in the line output stage and they were an absolute bugger to diagnose ,often failing Again after 2 weeks of soak test. Dont miss that one ha

@fffsfdsf Жыл бұрын

Just wonder did you find the correct adj resistor,if not,i nned that original resistor's rod length to find a compatible one

@ovalteen4404 Жыл бұрын

Ah, bad connectors. A friend had a monitor that kept shutting off at random times. It would turn on again after a while, or smacking it typically brought it back. I looked at it. The signal cable connected internally to a bunch of plug connectors. By sheer luck I noticed that one of them did not make great contact. So I soldered the plug to the pin and it was rock solid ever since. On another note, it's possible that the plug in that Mac needs new pins though. It's not always bad contacts. Sometimes the springs are too weak.

@TheFurriestOne Жыл бұрын

A hard-fought successful repair!

@HKSinha5100 Жыл бұрын

any update on 8" hard drive?

@coreybabcock2023 Жыл бұрын

I use a st 5000 VA step up n down transformer in my camper van its for the j1772 connection when Im at a car charging station to get power to run everything in the camper van

@mineyoucraftube1768 Жыл бұрын

the only thing that i was screaming for was you just touching stuff just after disconnecting the power without discharging the caps

@iRDaBrit Жыл бұрын

I want a tshirt that has "It's freakin' Workin'!" on it!

@coyote_den Жыл бұрын

That SCR is the crowbar. If +12 goes too high it will trigger the SCR and short the power supply out. The SCR will only turn off once the power supply shuts down, which produces the chirp-chirp-chirp sound if the over voltage condition remains. That SCR probably failed because the regulation went out of spec and kept cycling... it just kept dumping current until it finally blew up and shorted permanently.

@Renville80 Жыл бұрын

36:26 The squiggly line is the filament, and the box around it is the cathode.

@Nukle0n Жыл бұрын

I was wondering about that jumper lead, thinking oh well of course he reconnected that as part of the process, then, well...

@chetpomeroy1399 Жыл бұрын

*Safety First!* It's true that there *is* danger from voltage potentials from the inside of a CRT Mac, requiring one to take the necessary precautions, but at least there is no threat of lethal levels of ionizing X-radiation, such as that experienced by technicians repairing early color television sets.

@branhicks Жыл бұрын

I have that same tester. Does your documentation mention anything about that IR port? What's that for

@eDoc2020 Жыл бұрын

If you have a compatible IR remote (AFAIK NEC protocol, maybe RC5 protocol) it shows you the codes it sends. It's not a very useful feature.

@8-bitbitsa821 Жыл бұрын

Watching the start when you hook up the CRT tube…Don’t assume that a ground to the implosion band mount makes a connection to the aqua-Dag ! That’s not a given ! There’s a reason you see the braided grounding strap arrangement across the back of the tube. This is not just safety issue, it actually forms part of the anode high voltage circuit by using the “capacitance” of tube as part of the HV smoothing.

@foogod4237 Жыл бұрын

I don't know why that was tripping your GFCI, because it seems like it shouldn't have been anyway, but your step-up transformer is also arguably not wired right for this sort of appliance. It is common for 240 volt circuits in the US to have two hot legs, both at 120V relative to ground; however, for most other countries (Europe, etc) which use 220/240V, I'm pretty sure that the neutral wire should have a potential of (more or less) 0 volts relative to ground (and the hot should be 220/240V relative to ground). It looks like your step-up transformer is wired with the ground connected to a center tap of the output, which is not ideal. Instead, I would recommend connecting the ground straight through to the input ground, but _not_ to any part of the output of the transformer. This effectively turns your step-up transformer into a combination step-up and isolation transformer, and assures that (no matter what you plug into it) you will never have current travelling back along the ground line or elsewhere which could trip a GFCI. (Note that if you do this, then the output of the step-up transformer should show 0V between both ground-to-neutral and ground-to-hot (but 240V neutral-to-hot). This is normal, and is because both neutral and hot are now completely isolated from ground.)

@Stoney3K Жыл бұрын

I agree. In Europe, the "ground" is an earth and a protective earth only, which is isolated from the rest of the wires flowing current. On the circuit breaker panel, usually earth and neutral are connected together. There should be 230V between output hot and neutral, and the input windings should be hot and neutral only as well. Ground should pass straight through and also connect to the casing of the transformer.

@eDoc2020 Жыл бұрын

The step-up transformer has three leads internally, there's no way it can be used for isolation. However I agree he should make it be 0-240 output instead of 120-120. He probably just needs to swap the incoming live and neutral wires.