jgarland@kean.ucs.mun.ca (08/25/90)
Why does my Dell VGA (Mitsubishi 1429C, I think) get very bright, magnify letters, produce copious static from the glass and sometimes make snapping sounds from inside the case??? Is it going to BLOW??? Why does it settle down if I turn it off for a while??? It's 2.5 years old. Hardware types of the world, please help! John Garland jgarland@mun Bitnet jgarland@kean.ucs.mun.ca Internet
cramerk@motcid.UUCP (Kristin J Cramer) (09/01/90)
Your flyback is going It's a transformer that zips the voltage up to some 10,000 or so volts. You can if you can solder replace the flyback - BUT BE CAREFULL This is a job that has to be done with no power on. You must also short the picture tube (there is a special way - and if you have never done it I recommend you don't do it). The bottom line ... If it were mine - I'd buy a new one. Although..... It could be loose wire - but unless you have been moving the screen a lot (I don't mean turning) then it probably isn't Time to get a 19" super VGA display Kris OF course I may be wrong.
phys169@canterbury.ac.nz (09/05/90)
In article <128417@kean.ucs.mun.ca>, jgarland@kean.ucs.mun.ca writes: > Why does my Dell VGA (Mitsubishi 1429C, I think) get very bright, > magnify letters, produce copious static from the glass and sometimes > make snapping sounds from inside the case??? Is it going to BLOW??? > There are several possibilities. The least likely is a "noisy" brightness or contrast control. Try turning them slightly and see if the brightness jumps up or down sharply. It is faintly possible a bad contact on the wiper arm could affect screen size as well as brightness, but its worth trying (it is the easiest and cheapest to fix - either adjusting the control slightly or a squirt with inert switch-cleaning spray (CO) after turning off the power, should do it). Also consider dampness or dust inside the case. Switch off, leave off for at least an hour, unplugged from the mains, and vacuum very carefully (don't get the nozzel near the glass - it has a habit of suudenly sucking itself to the tube as you get close, with costly consequences). Putting the nozzel at the outside, over the ventialtion holes, every few months is a good idea. But, it's probably the line output transformer (a.k.a. lots of other names), or the transistor driving it. The time-dependant effect suggests more the transistor than the transformer, but the extra brightness suggests more drive, which could be the circuitry driving the transistor, feedback around the transformer, or power supply set to wrong local mains voltage. You could leave a bit of candle wax on both transformer and transistor and see which melts. BUT be very careful since the high voltages inside the case stay for quite some time after the power is turned off. It is best to get anything with CRT's fixed by the experts - it is safer and you should then get the proper part, rather than one that seems to work but is so overloaded it blows latter, taking down more circuitry with it. > Why does it settle down if I turn it off for a while??? > Can be transistors heating up and conducting too much, transformers heating up and insulation going, or possibly capacitors breaking down. It could even be driver circuitry near the high power stuff getting too hot. Dust and dampness problems also change with temperature, but usually get better rather than worse with time. All things considerred, the line (horizontal) driver transistor looks like the culprit, though; and that's best left to the experts. By the way, don't get too confident that "screen saver" programs allow you to keep your screen switched on for long periods without wear and tear; they save the phospher on the screen, but the rest of the monitor keeps running hot, and it can be expensive to fix too. If you leave a screen for an hour or more, it is certainly worth switching it off, (well, perhaps half a day in the case of well-designed mono screens). On the other hand, don't switch the screen on and off too many times each day, either; the greatest strain is during switch-on. Mark Aitchison, Physics, University of Canterbury, New Zealand.