Daewoo 901DN (?) CRT - the bad click

[gintama]

Gah... I seriously didn't want to be forced to move to LCD yet, but just now my monitor has started making a repeatable bad sound. I got this as an in-warranty replacement, and there's no label on it so I'm not even sure of the model number - I can only go by the box it came in.



Visually it's been fine, but every once in a while it will make a loud, high-pitched whine. This stops when I lightly slap the side of the case, or disappears on its own after 5-10 minutes. As well, over the last few months I've noticed a crackle sound and momentary picture dropout, as though something had momentarily shorted. This was rare though, maybe once every 150h that it was on.

At present, it has started making 3-4 very loud electrical clicks at every power on or when coming out of power-saving mode. When it is switched off, it continues to make a similar number of similar sounding clicks every few seconds. During each click the "static burst" that can normally be heard from the glass plate on shutdown stops completely, and a second after the click it starts up again. There is also a perceptible difference in the sound made when the display output changes contrasts suddenly. I thought it might be the degauss system, but this seems to work normally when triggered from the OSD. Additionally, it is now dropping the picture for several hundred ms every 15 minutes or so.

Here's a (poor quality, sorry) sound file in case anyone cares to hear: mp3 @ binarybooty.com

00:01 - power off
00:11 - power on
00:14 - normal degauss completion sound
00:17 - power off
00:27 - power on
00:30 - normal degauss completion sound

Most of you seem a fair bit more knowledgeable about electronics repair, so I figured I'd see if anyone has any suggestions. Thanks!

[kc8adu]

Re: Daewoo 901DN (?) CRT - the bad click

flyback will die soon.
those clicks are arcs inside it.
shop for a replacement and change it before it dies.

[Toasty]

Re: Daewoo 901DN (?) CRT - the bad click

Also check the soldering in the horizontal and high voltage sections. The tapping on case to stop noise sounds like you have some cold solder joints.

[gintama]

Re: Daewoo 901DN (?) CRT - the bad click

Those are... both very specific answers. Cool! I also appreciate that someone who doesn't know anything about tube displays will have no idea what you're referring to. I will read up on it (and probably shop for an LCD display as well), but I imagine this may be a repair that's fairly dangerous due to the HV caps present. Would a safe flyback replacement require discharging these, or just exercising heightened caution? How similar would the replacement part have to be? And how much would a trained professional be likely to charge for the swap?

Now, I also have a TV with tuner issues... Maybe someone will know the problem there as well. It's a 20" Trinitron from ~1993, and the 'Video' input works perfectly. When switched to the 'Tuner' input (from Video mode or from power off state), the display horizontally rolls bursts of static across the screen, with accompanying audio from the speakers. There doesn't seem to be any physical noise coming from the set that accompanies this - if the volume is muted there's only the distorted picture. This usually subsides within one hour of being in tuner mode, the perfect amount of time to miss the show you turned it on to watch. Also of note, the set could have been on for days on the Video input, but this does not diminish or circumvent the problem. Video is here: http://www.youtube.com/watch?v=M7P6SLoVM6A - there's no sound but I'm sure you can imagine it fine. I really wish I'd noticed this subforum sooner.

[Scenic]

Re: Daewoo 901DN (?) CRT - the bad click

^ last time i saw that it was simply cold solder joints on the tuner module..
also on a sony.. but idk what model that was.. looong time ago..

that "clicking" sound is the flyback as kc said.
i wouldn't force it to do that clicking (by turning it on and off more often than needed) unless you wanna end up with no monitor at all

same reason why so many early CRT iMacs and eMacs died.. turning them into a useless block of plastic.. (and a heavy one at that)

edit: my own iMac did the same thing, but as it's an all-in-one unit, it's really a painus in the anus..

everytime the flyback arced, the powersupply for the CRT part completely turned off. not exactly a bad thing. problem was: the actual computer was still running fine.. you just couldn't see anything cause the CRT PSU shut off.

sitting there, doing something (writing a text or whatever).. then suddenly the flyback arcs again, CRT PSU shuts off, and the only thing you could do was pull the plug and start all over again..
happened to me quite a few times.. having a webradio stream playing typing something, CRT turns off and i ended up with an uncontrollable music-playing plastic box

[gintama]

Re: Daewoo 901DN (?) CRT - the bad click

Yeah, the Sony has already had some issues with the solder - the yellow RCA connector on the input board was flaky for a long time. Had to completely remove the old solder to get it to work properly, the stuff that was there just wouldn't give a solid connection no matter how many times it was re-melted.