cayz@udel.edu (James Cayz) (08/28/90)
All, Being somewhat technically oriented, I figured that the $30 investment in the book "Macintosh Repair & Upgrade Secrets" might be worth it. I do have questions, though... In the Safety Techinques Chapter, Mr. Pina shows a picture of a CRT Discharge Tool (1/8" screwdriver, wire, gater clip, & 10Mohm resistor), with the tools attached to the Logic Board Rails (p. 11)... Now, talking to a "Real Apple Technician", they said "No, attach it to the strap surrounding the tube.". Which (if not both) is more correct / safe? Normally, I would try it either way and see what happens, but since we could be talking blown parts (Mac and human :-( ), I'd rather be a little more cautious and get at least 2 opinions in agreement.... Also, on page 131, "Analog Board - Removal and Installation", step 2 is a little bothersome for me. It reads: "2. Physically disconnected the power cord from the wall outlet. If you're the least bit hesitant about discharging the CRT, leave the set disconnected overnight. By the next morning, most, if not all, of the high-voltage charge will have dissipated." Huh? Dissipated where? I had even heard that since it is just a static charge, a CRT charged would not lose it, but even when discharged, would become (slightly) charged by sitting out unconnected in a low-humidity area, requiring another discharge before re-connection. >>>>> Which is Truth, and which is Urban Legend? <<<<< Last Question: I'm slightly paranoid about being blown around the room by accidently discharging it across my hands. Is there any _harm_ to discharging it, lets say, whenever I work on / inspect / clean the dust out of the Mac?? Thanx for all the help in advance. James |James Cayz can be found via: USPS: Educational Technology Laboratory |EMAIL Internet: cayz@louie.udel.edu : 203 Willard Hall Education Building |PHONE: +1 302 451-6307 : University of Delaware, Newark DE 19716
barry@network.ucsd.edu (Barry Brown) (08/29/90)
In article <28710@nigel.ee.udel.edu> cayz@udel.edu (James Cayz) writes: > In the Safety Techinques Chapter, Mr. Pina shows a picture of a CRT >Discharge Tool (1/8" screwdriver, wire, gater clip, & 10Mohm resistor), with >the tools attached to the Logic Board Rails (p. 11)... Now, talking to a "Real >Apple Technician", they said "No, attach it to the strap surrounding the tube.". >Which (if not both) is more correct / safe? You're right; Mr. Pina doesn't tell the reader how to use the discharging tool. This is what I did (slight deviation from his diagrams): Since I expect to me opening my Mac several times, I permanently attached the 10M resistor to the ground chassis. If you look above the port connectors, you'll see a strip of heavy metal with large round holes in it. This is the ground chassis. Screwed into it will be a wire. I loosened the screw, attached one lead of the 10M resistor to it, and tighened it again. Now, to discharge my CRT, I merely clip one end of a test lead (the kind with aligator clips at both ends) to the free lead of the 10M resistor and the other end to the shaft of a flathead screwdriver. Holding onto only the plastic handle of the screwdriver, I worm the tip under the rubber "suction cup" until it contacts the metal underneath. Then I hold it there for several seconds until I'm satisfied that all the charge is dissipated. Then I unclip the test lead, leaving the resistor attached for the next time I need to discharge the CRT. > Also, on page 131, "Analog Board - Removal and Installation", step 2 is >a little bothersome for me. It reads: >"2. Physically disconnected the power cord from the wall outlet. If you're the >least bit hesitant about discharging the CRT, leave the set disconnected >overnight. By the next morning, most, if not all, of the high-voltage charge >will have dissipated." > > Huh? Dissipated where? I had even heard that since it is just a >static charge, a CRT charged would not lose it, but even when discharged, would >become (slightly) charged by sitting out unconnected in a low-humidity area, >requiring another discharge before re-connection. It's not a static charge. It's an honest-to-God 15,000 volt charge, like that contained in a very big capacitor. It's not something you want to touch, nor is it something you just want to short out. That's why you need the 10M resistor. If you don't use the resistor and just short out the CRT, you'll get a big spark and a couple of blown chips on the logic and analog boards. As Larry Pina puts it, that's COSTLY. > Last Question: I'm slightly paranoid about being blown around the room >by accidently discharging it across my hands. Is there any _harm_ to >discharging it, lets say, whenever I work on / inspect / clean the dust out of >the Mac?? Nope. In fact, it's a damn good idea. -- Barry E. Brown -- \ Cal-Animage Beta publicity officer bebrown@ucsd.{edu,uucp,bitnet} \ Anime Stuff FTP Server administrator Somewhere in University City.... \ (ftp network.ucsd.edu [128.54.16.3]) "Kaitsu! Kaitsu! Kaitsu! Kaitsukaitsukaitsukaitsu!" -- Azusa (Ranma 1/2)