Discharging the CRT in a compact Macintosh
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- เผยแพร่เมื่อ 28 พ.ค. 2024
- All old compact Macintoshes contain a cathode ray tube (CRT) inside the case. The CRT can hold a lethal charge, even when the computer has been switched off and disconnected from the power. The steps described in this video demonstrate how to build your own discharge tool and safely discharging that electricity.
Disclaimer: I can't accept any responsibility if you decide to follow these steps.
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Having zapped myself with an SE's CRT last year (and one that had been completely unplugged for a day)... I appreciate this video.
Glad you're still with us!
@@BranchusCreations a family friend did this but was killed from trying to remove a crt from a 50s tv. thats what makes me so skittish about trying it.
@@macgeek21 I'm not saying this to stop you from exercising necessary caution, but the voltage in a little compact Mac CRT is much smaller than a 50s TV. I have had plenty of people who have told me they got zapped by a compact Mac and they are still around to tell the tale. Sorry about your family friend.
Thanks for the video! Great camera work, that really helps to see how things work.
Fantastic. I discharged my SE/30 for the first time a few months back with no surprises, but I would have enjoyed watching this first.
Hello Bruce! Thank you for a very educational procedure on CRT discharging. It's good to know that folks now have a very good reference that not only describes the process but why it is important to be safe. Beautiful cat by the way! Cheers and thank you for another fantastic video.
One caveat: I like to use an aligator clip on the screwdriver side too instead of taping the bare wire; it saves the need to sacrifice a screwdriver and tape, especially if you don't do this often.
Bruce the Mac Yak crew just stumbled across this video... this is some grade A quality stuff man! Your production quality alone is leaps and bounds over my stuff alone keep it up! We’d love to chat with you on Mac Yak some Friday Morning (your time... it’s Thursday night for us lol) if you’re interested let us know!
Thank you! I would be more than happy to chat Mac Yak!
Excellent tutorial on this subject.. Thanks. I always hate working around High Voltages.. lol
Thanks much! An older video but as I gear up for finally work on some compact macs this'll be invaluable. I have to be honest I've heard about how dangerous CRTs are for so long that it nice to get some real info on how to mitigate it (I think the FIRST time I heard about CRT danger was the old old old macquarium guide from the early 90s when I was a wee lad and it stuck)
Really useful. I've worked with CRTs my whole life and I don't think I've ever properly discharged a CRT. I count myself lucky not to have killed myself. I also heard you should place the other hand in your pocket.
Feedback that this was an excellent, straightforward, and informing video on Compact Mac CRT Discharge. You covered it all and backed it with Apple's own guidance -- smart! I know there are many opinions around this, but your method was clear and worked great.
,"Firecracker discharge indicates open magnetron windings" I will always remember that statement from the G.E. field service guide, whom I worked for as an appliance tech, 30 years ago.
That statement is very true. Sometimes it sounds more like a bullwhip. Oh, its referring to microwave oven diagnoses and repair, and discharging the high voltage capacitor inside the unit. 🤓
Thanks so much for this! Hands down the best and most informative video I've seen about the procedure. I'm about to work on my Mac Plus and wanted to brush up a bit more on my CRT discharging knowledge after reading up in the service manual. A quick web search brought me here. I'm definitely going to refer to your video when I release the video about my own (hopefully successful) Mac Plus repair. :)
Thank you for another great video, Bruce!
Most Excellent. THANK YOU
Thanks for the advice - great video tutorial. I watched this as I need to discharge my Apple Studio 17 CRT as it's constantly popping & causing the picture to expand and go dark for a couple of seconds. Assuming it's the flyback transformer but thought I'd try cleaning away the significant dust build up inside first.
Nice video, but when using the wire without the resistor, you stand a higher chance of blowing the 7438/LS38 IC on the analog board when discharging the CRT. (Former tech at a gray market repair depot '93 - '97)
Excellent video, clearly explained. Thanks for your work.
Thanks for this video ! Very detailed !
Thanks for your informatry video....
Very professional and educational. Thanks!
Thank you for your this. Very clear instruction and good safety tips. Now to get to work on my Classic 2!
great domo on how to make a discharge tool :)
Thank you for this. I have an iMac G3 that needs it's CRT discharged so I can safely work on the inside of it.
That was actually very interesting!
Can't go wrong with Apple's own recommended procedures! Would love a demonstration at some point of adjusting the voltage for a 128/512/Plus. I wonder if the European/Australian units differ from the ones here in North America, like the mains voltage.
Interestingly, Larry Pina recommended in his repair book to use a bleeder resister, so I went with that. But that does make sense about wanting to hear the pop of the discharge!
There are quite a few differences in the US and International versions of the analog board, but the voltage adjustment procedure is the same for both. I'll add a voltage adjustment procedure video to my request list!
@@BranchusCreations Hi Bruce and Nate, I thought I should mention another really fine chap who publishes very good content on Macintosh related repairs as well. His channel is here, th-cam.com/channels/QlrWbkbU-N-HddTe_Ydajw.htmlvideos. He is an American expat living in Japan. Wishing you both a beautiful day. Cheers!
Thanks for the info and the alerts your life is important here.
Thank You very much for your video!
Thanks for your explanations, it’s very clear. Nice cat :)
Great Video, I am hoping you can add a detail. I know that the coating inside the CRT makes the Anode and the coating on the outside is the Cathode with the glass acting as the dielectric of a large capacitor. Does the neck board need to be connected to get a complete circuit when discharging? I am not measuring a connection between the cathode and the ground lug without it!
Great video
Many thanks for this tutorial. I recently picked up my first Mac Classic which badly needs a full recap so I'll need to discharge before stripping down. Beyond hearing a spark can you recommend any procedure to prove that the HV has discharged, would I need an HV probe to do this?
I've never actually tested after discharging, and have just trusted in the discharge tool. However, if you have concerns, just leave the computer unplugged overnight before touching anything.
Just subscribed because of this excellent video. Do you have a link for the document you used from Apple?
I followed your advice and successfully opened up my 512k. Discharged at the anode. No spark (I left the machine off for weeks prior) but I feel better following your example. I'm writing 1) to thank you! and 2) Do you know where can I go to learn what capacitors can burn out and mess up the display? My symptom was screen "clicking", then a cap burning smell. Then the display worked but it was off to one side and the font was huge and distorted. I don't see any obvious caps burned, and I could be wrong, but it sure smelled like a cap took a well, you know.
1) You're welcome and thanks for watching! 2) That symptom actually sounds more like the flyback transformer than a capacitor. Unfortunately replacement flybacks can be rather hard to find, and you may have to salvage one off another Mac (128k, 512k or Mac Plus have the same one). I would also inspect all the solder joints on the analog board, as it's very common for these old Macs to develop cracks, resulting in all sorts of problems - especially with the display.
@@BranchusCreations I found a flyback transformer from a company in Florida. Worth a shot, I figure. Now to start practicing my skills.
I just wanted to do a follow-up. After finding a flyback replacement I practiced soldering/desoldering on some scrap boards and then finally went for it. First time doing this level of repair. Well, it worked out wonderfully! Your diagnosis of the flyback transformer was spot-on, and now this 512k Macintosh is alive again with a bright, crisp display! Thank you very, very much for pointing me in the right direction.
@@lanatrzczka Great to hear, congratulations!
Have you worked on Apples studio display crt monitors before? Having issue with flickering
BRANCHUS CREATIONS, why does the B+ voltage need to be set correctly or the monitors H&V sync signals will not LOCK and display a scrambled images?
I heard that the glass tube is the one what contains the energy, not the flyback, because the flyback is a transformer and the transformers doesn't store energy (sorry for my english)
Yes, that is my understanding as well. When the CRT is being discharged, it is the tube that's being discharged, not the flyback.
Hi Bruce, I´d like to know what is the name of the part or part number for a Macintosh Classic Model M0420 flyback transformer. Thanks!
Ahhh d*mn .. I also did a video on this process (german dubbed) but didn't upload it yet xD ...anyway, I will do so too soon - you really did a great explanation and demonstration here :D
The glue on the flyback looks bad and it looks like it is starting to absorb water, so I would remove it or replace the flyback
so what he warned about happened to me today. i was trying to open a SE that had an issue with the monitor it took a lot of force and some opening tools to finally get the case off once that happened i heard a woosh first i thought i was gonna die but i now know that was the vaccum being broken.
if that happens to anyone else watching this video the crt is now safe since the vaccum was broken but i would still discharge.
Its better you know what you doing it. It can be dangerous
Aim breking glas
Just stick a fork in it
What's the worst that could happen?
death