4 ms·

You need(ed) to drain any lingering charge in the CRT. It was easier and safer to do this with a dedicated tool than e.g. with a screwdriver, but the latter wo

You need(ed) to drain any lingering charge in the CRT. It was easier and safer to do this with a dedicated tool than e.g. with a screwdriver, but the latter worked for one-off jobs. Ground the probe or screwdriver, then slide it under the rubber cup shielding the... good-grief, I've forgotten which. Anode connection of the tube. The tube/circuit could/can carry considerable charge for a significant period of time. Simply unplugging the mains power lead was not sufficient protection for a person working inside the case. But, the case was "easily" open-able -- aside from complaints about the non-standard screw heads and difficulty separating the halves if you didn't have a tool to insert into the seam and pry them apart. And once you were inside, things were pretty accessible. There was even an entire cottage industry documenting and recommending/selling replacements particularly for analog components on the power board, some of which were perhaps a bit under-spec-ed in the original designs and prone to noticeable deterioration as well as outright, total failure.

joosters 13y ago
I'm not saying it was impossible to safely open these machines. After all, there were plenty of people safely working in TV repair shops. If you knew what you were doing and weren't sloppy, you would be perfectly safe. The problem is, not everyone would know what they were doing. At least with current tech, the worst that can happen is you ruin your computer and not your life.
- pasbesoin 13y ago
  Well, perhaps in a meta sense, the older designs "repaired" (us) by thinning the herd. ;-) One the one hand, I take your point. On the other, people wrote books documenting the whole thing and you could replace that defective capacitor yourself. (Significantly less expensive than having a technician swap the power/video board, particularly if you did not have AppleCare. And you could replace it with a more robust part, so that you were not in the same circumstances again 6 months or a year later.) I guess with the relative decline in price of whole subsystems -- in some cases -- these days, the greater availability of those, and -- again, in some cases -- the personal safety if not always ease of swapping them out, something might be said for "increased repairability". On the other hand, I don't think the Classic Mac design rates a 0/10. Lots of things back then could kill you. These days, you can't even purchase a real chemistry set for your kids, or in some cases hardly glassware for yourself.
- kens 13y ago
  You might think a laptop is harmless inside, but it actually contains 500-700 volts to power the LCD backlight. I learned while trying to fix my display - fortunately I found it out by reading, not by getting shocked. Unlike when I stuck my finger across the flash capacitor in a camera - yow! The point is, even harmless-seeming battery powered things can have surprisingly high voltages inside, so be careful.
  - rosser 13y ago
    You might think a laptop is harmless inside, but it actually contains 500-700 volts to power the LCD backlight. How many CCFL-backlit laptops are they shipping these days? EDIT: Also, high voltages, on their own, aren't necessarily dangerous. Tesla coils can run into the tens of kilovolts, but can be perfectly safe if they're properly constructed.
kps 13y ago
good-grief, I've forgotten which Just remember it's a CRT, so the CRs come from the C at the back of the T.
jotm 13y ago
Oh, I just remembered being shocked by that damn cable running from the flyback transformer - that was really unpleasant!
mattkevan 13y ago
I worked in a TV repair shop in the early 90s. The firstt thing they taught me was to discharge CRT. Leave the TV plugged in but off at the mains, get two big screwdrivers, touch the end of one on the outside of the tube (which is coated in graphite and earthed), slide the tip of the second under the cathode cap and bring the two together. It'll discharge with a sharp crack. We had to do that every time we started work on a TV just in case it'd been switched on. That was a fun place to work. The guy who ran the place hated people touching his tools so he'd charge up a fat capacitor and drop it in his toolbox. Anyone rummaging unwarily soon learned a lesson.

joosters 13y ago

I'm not saying it was impossible to safely open these machines. After all, there were plenty of people safely working in TV repair shops. If you knew what you were doing and weren't sloppy, you would be perfectly safe. The problem is, not everyone would know what they were doing. At least with current tech, the worst that can happen is you ruin your computer and not your life.

pasbesoin 13y ago
Well, perhaps in a meta sense, the older designs "repaired" (us) by thinning the herd. ;-) One the one hand, I take your point. On the other, people wrote books documenting the whole thing and you could replace that defective capacitor yourself. (Significantly less expensive than having a technician swap the power/video board, particularly if you did not have AppleCare. And you could replace it with a more robust part, so that you were not in the same circumstances again 6 months or a year later.) I guess with the relative decline in price of whole subsystems -- in some cases -- these days, the greater availability of those, and -- again, in some cases -- the personal safety if not always ease of swapping them out, something might be said for "increased repairability". On the other hand, I don't think the Classic Mac design rates a 0/10. Lots of things back then could kill you. These days, you can't even purchase a real chemistry set for your kids, or in some cases hardly glassware for yourself.
kens 13y ago
You might think a laptop is harmless inside, but it actually contains 500-700 volts to power the LCD backlight. I learned while trying to fix my display - fortunately I found it out by reading, not by getting shocked. Unlike when I stuck my finger across the flash capacitor in a camera - yow! The point is, even harmless-seeming battery powered things can have surprisingly high voltages inside, so be careful.
- rosser 13y ago
  You might think a laptop is harmless inside, but it actually contains 500-700 volts to power the LCD backlight. How many CCFL-backlit laptops are they shipping these days? EDIT: Also, high voltages, on their own, aren't necessarily dangerous. Tesla coils can run into the tens of kilovolts, but can be perfectly safe if they're properly constructed.

kps 13y ago

good-grief, I've forgotten which Just remember it's a CRT, so the CRs come from the C at the back of the T.

jotm 13y ago

Oh, I just remembered being shocked by that damn cable running from the flyback transformer - that was really unpleasant!

mattkevan 13y ago

I worked in a TV repair shop in the early 90s. The firstt thing they taught me was to discharge CRT. Leave the TV plugged in but off at the mains, get two big screwdrivers, touch the end of one on the outside of the tube (which is coated in graphite and earthed), slide the tip of the second under the cathode cap and bring the two together. It'll discharge with a sharp crack. We had to do that every time we started work on a TV just in case it'd been switched on. That was a fun place to work. The guy who ran the place hated people touching his tools so he'd charge up a fat capacitor and drop it in his toolbox. Anyone rummaging unwarily soon learned a lesson.