gil@limbic.UUCP (Gil Kloepfer Jr.) (08/19/88)
In article <593@proxftl.UUCP> aaron@proxftl.UUCP (Aaron Zimmerman) writes: |>My 3b1's monitor (you know, that ugly GreenScreen...) has a sore case of the |>bounceys. Sometimes it will decide to sort of vibrate up and down. This happened to me with a DEC VT220 Video Terminal several times. What happens is that (for some reason) the horizontal hold potientiometer inside the unit got flaky from being in the same position for a long period of time (add humidity and temperature variations). A really silly fix that worked was to shut the unit off and to work the pot back and fourth a couple of times with a screwdriver, putting the control back to its original position when finished. After performing this feat, you should readjust the pot (with the power on :-{) so that the screen is pleasing to the eye and doesn't produce any annoying high-pitched squeeks. I'm going to cross-post this one to sci.electronics to see if someone in electronic-land has a more permanent solution. +------------------------------------+----------------------------------------+ | Gil Kloepfer, Jr. | Net-Address: | | ICUS Software Systems | {boulder,talcott}!icus!limbic!gil | | P.O. Box 1 | Voice-net: (516) 968-6860 | | Islip Terrace, New York 11752 | Othernet: gil@limbic.UUCP | +------------------------------------+----------------------------------------+
hoffman@pitt.UUCP (Bob Hoffman) (08/25/88)
In article <593@proxftl.UUCP> aaron@proxftl.UUCP (Aaron Zimmerman) writes: >My 3b1's monitor (you know, that ugly GreenScreen...) has a sore case of the >bounceys. Sometimes it will decide to sort of vibrate up and down. One possible cause may be similar to that which afflicts many of our Zenith and DEC CRTs: bad solder connections. The symptoms are that the display will begin to vibrate or fold over itself. If left alone, the condition worsens until you have a single vertical or horizontal line, or no screen image at all. What is happening is that the solder holding a joint cracks, creating a high-resistance connection. Heat is generated by this resistance, causing the crack to widen. Eventually, the connection begins to arc, causing even more damage. Look at the solder side of the PC board which contains the high-voltage sweep components. The problem seems to affect the larger components on the board, particularly connectors, coils, and transformers. The bad connections look like a dark ring around the component pin. Also note any discolored areas of the PC board. These indicate excess heat in that area. It's not a bad idea to take a soldering iron and some good solder and re-flow the joint at each of the pins of those components. I have repaired many "dead" CRTs this way and have not had to replace any components. Simply re-flowing the solder connections fixed them. ---Bob. -- Bob Hoffman, N3CVL {allegra, bellcore, cadre, idis, psuvax1}!pitt!hoffman Pitt Computer Science hoffman@vax.cs.pittsburgh.edu