gwoho@nntp-server.caltech.edu (g liu) (11/07/90)
i had an amiga monitor that quit working after 4 years of being on, so i took it apart and tried to fix it. it turns out that a strange looking temperature sensitive resister thing went bad. this is wat it was for: when the computer is turned on, the resistor is cold, so it lets lots of current go through a coil that is in front of the crt. after 1 sec, it gets hot, and the current shrinks, and it demagnitizes the metal chunks around the crt. the resistor was shorting, so i got rid of it. but now, the screen is a bunch of strange collors. how could i make it good again? also there is quite a big scratch on the screen. is it possable to fix it? thank you in advance for sugestions. gwoho liu.
bender@oobleck.Eng.Sun.COM (Michael Bender) (11/07/90)
In article <1990Nov6.233222.8908@nntp-server.caltech.edu> gwoho@nntp-server.caltech.edu (g liu) writes: >i had an amiga monitor that quit working after 4 years of being on, >so i took it apart and tried to fix it. >it turns out that a strange looking temperature sensitive resister thing >went bad. >this is wat it was for: when the computer is turned on, the resistor >is cold, so it lets lots of current go through a coil that is in front >of the crt. after 1 sec, it gets hot, and the current shrinks, and it >demagnitizes the metal chunks around the crt. >the resistor was shorting, so i got rid of it. but now, >the screen is a bunch of strange collors. how could i make it good again? >also there is quite a big scratch on the screen. is it possable to fix it? >thank you in advance for sugestions. >gwoho liu. I can't help with the scratch, but for the resistor, you could try substituting a momentary push button switch, optionally with a fixed-value resistor in series with the switch if the miniumum reistance of the original resistor was much greater than a few ohms. Another trick might be to build a one-shot and use that to drive a relay, so that even if you held the push button down, the one-shot would limit the amount of time that the degausser coil was energized. Of course that wouldn't stop you from continually pushing and releasing the switch, but then again you can break anything if you try hard enough. I suppose that you could also buy or borrow a TV degaussing coil and run that in front of the crt. mike -- Won't look like rain, Won't look like snow, | DOD #000007 Won't look like fog, That's all we know! | AMA #511250 We just can't tell you anymore, We've never made oobleck before! | MSC #298726
edhall@rand.org (Ed Hall) (11/08/90)
In article <2262@exodus.Eng.Sun.COM> bender@oobleck.Eng.Sun.COM (Michael Bender) writes: >In article <1990Nov6.233222.8908@nntp-server.caltech.edu> gwoho@nntp-server.caltech.edu (g liu) writes: >> . . . . >>this is wat it was for: when the computer is turned on, the resistor >>is cold, so it lets lots of current go through a coil that is in front >>of the crt. after 1 sec, it gets hot, and the current shrinks, and it >>demagnitizes the metal chunks around the crt. >I can't help with the scratch, but for the resistor, you could try >substituting a momentary push button switch, optionally with a fixed-value >resistor in series with the switch if the miniumum reistance of the original >resistor was much greater than a few ohms. Don't do this! There is a reason why they used that particular mechanism. The current through the coil must be reduced *gradually* or else it might wind up making matters worse (i.e. instead of a DEmagnetizer it would become a magnetizer.) It shouldn't be too hard to find a replacement thermistor; just about all high-quality CRT's (and even TV sets) use a similar mechanism. -Ed Hall edhall@rand.org
bender@oobleck.Eng.Sun.COM (Michael Bender) (11/08/90)
In article <1990Nov7.230205.2520@rand.org> edhall@rand.org (Ed Hall) writes: ..>In article <2262@exodus.Eng.Sun.COM> bender@oobleck.Eng.Sun.COM (Michael Bender) writes: ..>>In article <1990Nov6.233222.8908@nntp-server.caltech.edu> gwoho@nntp-server.caltech.edu (g liu) writes: ..>>> . . . . ..>>>this is wat it was for: when the computer is turned on, the resistor ..>>>is cold, so it lets lots of current go through a coil that is in front ..>>>of the crt. after 1 sec, it gets hot, and the current shrinks, and it ..>>>demagnitizes the metal chunks around the crt. ..>>I can't help with the scratch, but for the resistor, you could try ..>>substituting a momentary push button switch, optionally with a fixed-value ..>>resistor in series with the switch if the miniumum reistance of the original ..>>resistor was much greater than a few ohms. ..> ..>Don't do this! There is a reason why they used that particular mechanism. ..>The current through the coil must be reduced *gradually* or else it might ..>wind up making matters worse (i.e. instead of a DEmagnetizer it would ..>become a magnetizer.) It shouldn't be too hard to find a replacement ..>thermistor; just about all high-quality CRT's (and even TV sets) use ..>a similar mechanism. ..> ..> -Ed Hall ..> edhall@rand.org you're right - my friend Jeff warned me about this last night on the phone after I told him what I posted. you could always do a high-tech degausser, using one of the uP's that we've been talking about on the net for a few weeks and a D/A converter and a power amp; that way, you could have a virtually unlimited type of ramp-down. maybe you could even add a hall-effect sensor to the circuit so that if the ambient magnetic field got strong enough past a (user-defined) threshold, the uP would power up the degausser. mike -- Won't look like rain, Won't look like snow, | DOD #000007 Won't look like fog, That's all we know! | AMA #511250 We just can't tell you anymore, We've never made oobleck before! | MSC #298726