BAXTER_A@wehi.dn.mu.oz (09/03/90)
In article <1195@tardis.Tymnet.COM>, jms@tardis.Tymnet.COM (Joe Smith) writes: My original problem was a momentary alteration in the aspect ratio of the screen associated with a bzzzt sound. > > Take off the cover of the 2002 and look at it from the back. Examine the > printed-circuit (PC) board. To the left you should find the power connector, > the audio connector, and the chroma/luma video connectors. That corner of the > PC board is grounded and shielded by a piece of metal that is soldered on. > > To the right you should find an "L" shaped aluminum heat sink with a power > transistor bolted to the right-hand side. (The planes of the heat sink are > vertical and surround the flyback transformer. A thick red wire comes out > of the flyback transformer and connects to the upper side of the picture > tube.) > This cable is co-ax, and the insulation has been stripped and the "earth" shielding is clamped to the heat sink with a small clip. > If you look under the printed circuit board, you should see two screws > holding the heat sink to the PC board, and a bent metal tang that goes > through a hole and also holds the heat sink down. No screws, 4 bent tabs. >I saw evidence of an > electrostatic discharge that jumped from the metal tang to one of the copper > traces on the PC board. This is the cause of the "snap" and "pop". > The heat sink is not electrically connected to anything, and accumulated > an electrostatic charge until it arced over. > I saw arcing on the _top_ side of the board, between the flyback transformer and the heat sink. > I simply ran a wire from one of the screws that holds the heat sink to the > PC board over to a screw by the input connectors. Make sure the wire is > insulated so as to not short out anything else on the PC board. I used > an ohm-meter and verified that it showed zero ohms between the heat sink > and the grounding shield. "Poof", no more pops! > -- A little bit puzzled, I ran a wire from the clip that connects the coax cable shielding to the braided "earth" that surround the picture tube. Monitor worked fairly well for a few hours, then bzzzzzzzzzzzzzzzzzzzttttt... and complete loss of picture. Picture returned with a good thump on the side of the case. Haven't opened it yet, but seems like the transformer is arcing to earth, not to a charged heat sink. Any suggestions? > Joe Smith (408)922-6220 | SMTP: jms@tardis.tymnet.com or jms@gemini.tymnet.com > BT Tymnet Tech Services | UUCP: ...!{ames,pyramid}!oliveb!tymix!tardis!jms > PO Box 49019, MS-C51 | BIX: smithjoe | 12 PDP-10s still running! "POPJ P," > San Jose, CA 95161-9019 | humorous dislaimer: "My Amiga speaks for me." Regards Alan