More weirdness from my 15v2000. This time smoke...

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More weirdness from my 15v2000. This time smoke...

Okay, after some valuable assistance from some great and knowledgeable KLOVers, there is another chapter to my 15v2000 saga:

It was looking great, and everything was going well. Then after a week or so, I started to get some different strange behavior:

At boot, the image grew to what I would describe as "Full bloom" within about 10 seconds of becoming visible (the middle third or so of the image fills the screen in both X and Y), and there is a bright dot in the center of the screen.

I got a whiff of "hot component" and shut the game down until I could look more closely. When that finally happened, I assumed it was the HV diode, so I replaced it. The behavior continued, but as the monitor was out of the cab, I was able to see a wisp of smoke emanating from R900 (the big resistor) on the HV board. The PCB was also a bit scorched where R900's legs are attached.

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Some additional data: When I initially pulled the monitor apart to recap and clean it, I did not use any grease to re-pack the HV diode, nor did I use any when I installed the replacement. My understanding is that the dielectric grease is there to prevent corrosion, not to facilitate the connection (wrong?).

I also used some Goof-Off to clean the flyback connector and the surface of the tube around the anode. This is also how I cleaned the springs on the HV diode connectors.

Does anyone have any ideas about what might cause R900 to smoke?
 

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Okay, finally back at my bench.

Following iankellogg's advice, I went short hunting. I couldn't find any obvious solder splash or anything, but in testing the Q900 transistor, I did find a suspicious reading:

Using my DMM in diode test mode, from base to emitter I got 0.384v. The guide I was using said that this should be between 0.45v and 0.9v.

In my experience, when I find a failure, it's usually something much more spectacular than a part reading slightly outside limits, it's generally much more obviously and catastrophically wrong.

So could this be my problem?

Or is this like having your bad cholesterol one point above the max: not desirable, but also not likely to be the cause of death?

Thanks as always everyone!
 
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That .45-.9 thing is pretty meh advice. If its not like 0V and not OL then its probably fine. There are diodes that when measured will read 0.10V and that's normal. Anything above 0.3V is within range on that.

Tracking down shorts like this can be challenging.
 
That .45-.9 thing is pretty meh advice. If its not like 0V and not OL then its probably fine. There are diodes that when measured will read 0.10V and that's normal. Anything above 0.3V is within range on that.

Tracking down shorts like this can be challenging.

That is very useful and helpful. I'll keep poking around, thanks! (also,

On a related note, while chasing things down, I came across L900, which is an adjustable inductor. The B&W FAQ suggests that this part isn't necessary for correct operation of its circuit, but just in case, can anyone tell me how to test this guy?

Again, thanks so very much!
 
This one just won't seem to die. I've tested all the transistors, and they all seem to be working.

Is it possible that the flyback could be causing this?

That's got me worried, since it is, as far as I can tell, the only part that is officially unobtanium.
 
Is that resistor within spec?

Sorry, I was incommunicado for a few days.

It seems to be in spec when I test it in circuit, although I can't imagine it can let all that smoke out and still be "right". I'll pull it and check. Thanks for the suggestion!
 
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