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Couple of Compact CRT questions

beachycove

beachycove

68030
Couple of questions from a CRT ignoramus:

1. I have an SE with bad screen burn. Can this screen in the SE be replaced with a Plus screen? I have a spare, dead Plus and think the SE a better machine to preserve, on the whole.

2. A failed analog board transplant into a Classic II means I have to try again. For how long does the CRT/ HV circuitry retain a charge, unplugged? I'd want to wait until being sure there is no danger before disassembly and re-attempting repair.

 
1) For the most part, yes. But you should take note the CRT Tube numbers and see if they match; they should. The socket should should also fit as well. The problem, if any, is the yoke assembly and the holding tabs.

But you should save your crt with burn because they are no longer being made, and having a CRT with burn is better than having no screen at all.

2) For me, a minimum of 4 days, even though Classic/Classic II has a flyback transformer with a bleeding resistor which would drain it in a few minutes after being turned off. It is best to get/make a CRT Discharge tool and use it when you are not sure if the caps are charged or not. The problem is the Caps, they hold the charge what gets amplified by the flyback transformer.

Worse comes to worst, you can take the suction cup of the tube and bring it to one of the hold down screws if you think it is still charged. If it snaps or pops, it was charged and now has been discharged. Silence means that it was already discharged.

Now, what's wrong with the Mac Plus that is dead? I believe that most machines can be brought back to life. It depends on the resources and time one has to fix them. But... lets get the SE working and then the Classic II and then the Plus.

 
Thanks for that.

The dead Plus is probably a 128/512 that had the Plus upgrade (logic board and bucket), so it is not original and that, to my mind, makes it a candidate for parting out. Dead means, won't turn on at all, so I assume analog board problems.

I tend to agree that machines should be preserved, but in this case, someone could surely use the front bezel for repairs, I have a Mac 128 already, and I'd like to fix that SE. Plus, I have another proper Plus....

 
Elfen said:
 It is best to get/make a CRT Discharge tool and use it when you are not sure if the caps are charged or not.
Click to expand...
Agree!!! And it's pretty easy to make your own, so why not. :) I use one of these... attach the wire to the groundlug and slip the screwdriver under the suction cup to touch the metal. ehhh and just hold onto the handle and not the metal shaft of the screwdriver. lol.

discharge_toolE.gif


 
It's called a "Minus Screwdriver" because after discharging the flyback transformer a couple of times will chip the blade's tip and it will be useless as a screwdriver after that.

Unless you you got an electric grinding stone wheel to grind the tip back into shape.

 
not with a 100megohm resistor... however that resistor will take a very long time to discharge... Plus the flyback already has an internal resistor BTW.

 
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I think it's called 'Minus Screwdriver' because Japanese do.these picture were referred from famous SE/30 Repair page.and the writer is Japanese.I know it is kind of 'Japanese English' means no proper English but sounds like for Japanese... 

 
Huh, the funny part is that a Phillips, the way it is designed, is meant to cam out before you break the screw head off, unlike a real "Plus" flat ended driver that would give you great torque, but would def. snap the screw head off before the drive cams out if the max torque that the screw can handle is exceeded.

These days, a "Plus" would be more like a Pozidrive screwdriver.

 
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Hello. I'm new here and I would ask you a question: is it safe to manage a CRT monitor of a Mac 128k that has been turned off for 2-3 months or do I have to discharge it anyway? I don't know anything about electronics... Thank you very much in advance.

 
Thank you very much, Elfen.

I'm curious to see whether the 128k motherboard is the original one or not, since my father expanded the ram to 1Mb. I think that the expansion wasn't provided by Apple, but by another vendor, before Apple official program upgrades.

The Mac has been turned off in its original bag for about 25 years and when I turned it on 3 month ago it started without any problem. Only the 400k floppy drive initially made some strange noise, but then started loading Multiplan floppy drive smoothly! It was produced in the first months of 1984 (24th week of 1984) and it still works...

I wish my dishwasher lasts half that time... :)   

 
Last edited by a moderator:
Well 24th week would be more of a mid-year machine. The back would say Macintosh. If it says Plus, its had a motherboard/bucket transplant. If it still says Macintosh, then it could have the original board modified to 1mb. Best way to know is to open it and look at it. Having a 400k drive probably means its pretty close to stock though and would not have the Plus upgrade. Even still, it may not be the actual original board as some offered trad-in swap (like core exchanges) for upgrades. Basically boards on hand read to ship out once they get a core.

 
68k User said:
I'm curious to see whether the 128k motherboard is the original one or not, since my father expanded the ram to 1Mb. I think that the expansion wasn't provided by Apple, but by another vendor, before Apple official program upgrades.
Click to expand...
Sounds like a Dove Board to me though other companies made such boards as well. Dove Computer Products (I think is the name) have upgrades for the Mac, including a RAM Expansion for the 128K, 512K, and 512Ke. It connects to the Mac's CPU with a socket clip from above it. It is this clip, called a Kelly Clip, that fails in the upgrade many times.

Just be careful in removing the logic board from the metal frame as the with the memory upgrade things are going to be tight. So take your time and take it slow.

 
Using a Dove Board or similar RAM upgrade the original logic board is preserved. It's that the Kelly Clip clips onto the top of the 68K CPU and nothing else is supporting the add-on card to the logic board. In pulling the logic board out you can bump the RAM Upgrade and damage the Kelly Clip, the 68K CPU (or its soldered connections to the board), or both. So be careful doing this and take it slow.

The only issue you may have is whether or not that is a 128K board or a 512K board and the only way to find out is to open the machine.

 
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