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Old 11-19-2018, 11:35 AM
Shibby Shibby is offline
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Join Date: Mar 2017
Posts: 31
Well I was finally able to get my hands on a variac. A pre patent General Radio 20A 260v unit that looked like it was marked for military use for a cool $30. I'm pretty happy with that. Anyways as soon as I got it home I tested the variac on an unsuspecting fan to ensure it wasn't going to somehow kill my monitor even more. I then hooked it up to the monitor and slowly brought up the voltage.

The input lights slowly came on and it locked in on its default input 2. The fans started coming up slowly and I could hear various relays clicking. At about 80 volts I heard what sounded like high voltage but felt nothing on the front of the tube. It still had not yet gone into shutdown. Just past 80v I start to hear an electronic type noise that to me sounded like either arching or some type of short. The sound was coming from the DEF-PWB which I can only assume is the deflection board.

As I continued to ramp up the voltage the noise increased in volume and became more sporadic in that the tone was constantly changing. Then at about 100v the relay clicked and the monitor went into shutdown and the fans spun up to 100% as usual. I went through this process a few times which probably wasn't at all good for it but I couldn't help myself. The same thing happened pretty much every time. I did this with all the lights off at one point to see if I could see any arching of some type but all I could see were a few sparks coming from what I think was the degauss coil.

At one point I revved up the variac to just before where it usually went into shutdown and let it sit there for a few seconds. I then began to see smoke. Keep in mind that while doing this my only view was the bottom side of monitor with the bottom of the HV/PS-PWB and the DEF-PWB in view. There are a few passive components soldered and hot snotted to the bottom side of both of the boards. The smoke began coming from a resistor on the bottom side of the DEF board right around where the noise was coming from on the top side of the DEF board. The resistor was of course very hot but I think it was the hot glue around it that began to smoke and not the resistor itself. Anyways I of course shut it off immediately. From my very limited knowledge of what I am doing it seems to me that there is indeed a short on the Deflection board. To be honest while I did look the board over a good few times while still screwed into the chassis I never really inspected it thoroughly. When I got this monitor the HV Power Supply board was so mangled with leaky caps I thought for sure that was the issue. I had also not seen anything obvious capacitor wise on the deflection board so I didn't pay it much attention. Either way I will be pulling it out this evening and giving it a good once over. Now that I look at what all is on this board and what it does it seems sort of silly that I hadn't paid it more attention but I guess that's how it goes when you are learning. I will do my best to get the diagrams up of this board for you guys today just for reference but it may take a few as my work network and security systems tend to get a bit grumpy.

Anyways other than the obvious of looking for broken/burnt/leaking components any tips for helping to track down a potential short? Any idea as to what type of component might emit that type of noise? Anything I am not thinking of?

Additional Info: I was only able to get this result when slowly ramping up the variac. If I were to set the variac to say 80v and flip the switch the monitor would still go into shutdown. I believe this was still happening when set to as low as 60v. When I would slowly ramp up the variac I could get it up to around 100v before it would shut down. Am I somehow creating this shorting issue by not giving the monitor enough juice fast enough when ramping? Just trying to think through everything.
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