Dim K7000

LyonsArcade

Well-known member
Joined
Feb 9, 2006
Messages
19,367
Reaction score
3,854
Location
Rock Hill, South Carolina
Here's an interesting one, I've got a K7000 that was recapped and looked great, but when I went back to check it out after a couple hours, it was black. Still had neck glow, so I turned the brightness all the way up on the fly, and it looks great now, but everything's cranked to the max. B+ is dead on 130, and the input AC is at 120... the heater resistor looks fine too, so I'm thinking maybe the G2 is low? Anybody ever had that happen? It's got an old flyback on it (black knobs) can't tell if anybody's replaced it.

Is there a resistor that could have burnt up I can look for? I've never seen a G2 problem like this one.
 
What color are the knobs on the flyback?

EDIT: Oops, I read further and saw black knobs. Hm..not sure. Only thing I've ever seen act like that is a fly on its way out.
 
I have seen drifting focus and drifting brightness from failing flybacks.

How does the case of the flyback look, any cracks? Did you reflow the flyback pins during the cap kit?
 
Also, on K7000s you have a brightness and a contrast control pot that can affect the overall brightness of the picture. Are those 2 pots maxed out as well?
 
i have a tube that has this issue as well, the flyback is cracked and focus won't adjust as well as it being kinda dim. i also noticed that occasionally it will kind of flicker bright to dark to 1/2 and 1/2. glad you brought this question up i'll be watching this thread, and once i get around to mine i'll try and post my findings as well.
 
Well this one's kind of different though, I've had tons of games with bad tubes, or with drifting focus, or bad flybacks, or whatever, but this particular one went from great picture, to decent picture but only if you turn the fly, the contrast, and the brightness all the way up. So it's not the tube, it wouldn't have failed on all 3 guns over the course of an hour... and it's not the typical flyback thing because the flys usually fail catastrophically (they short the HOT and blow the fuse). I've never had a 'weak' flyback.
 
probably a whole other monster, but there's also that one resistor along the side of the neckboard that controls the heater. I had one K7000 where that developed cold solder. it was really weird cause it happened out of nowhere one day and a slight bang with my flashlight on the monitor frame made the picture come back for about 20 seconds before going completely black again. :p

I've also seen two variations of "black knob" flybacks: one has the usual knobs and another has phillips heads that you have to use a screwdriver to adjust. I've gotten both kinds now brand new, so I'm not exactly sure which is the definitive model to get or whatever. (sidenote: I think I've gotten both kinds from Bob Roberts, actually)

did you try wiping the Screen knob while the game's off and see if there's any change? I have zero tolerance for walking flyback controls, when that goes down I just pop for a new one.
 
I had a k7000 flyback that would become brighter and brighter till it showed raster lines on the screen, if I turned it off and let it cool down the picture would be back to normal. replaced flyback and problem was solved.
 
i to have an issue with a k7000 with a dim screen. i changed the caps and replaced with a known good flyback and it is still dim??
 
i to have an issue with a k7000 with a dim screen. i changed the caps and replaced with a known good flyback and it is still dim??

at that point it's probably your tube. :( you could try to bring it back by tinkering with the color pots, but that most likely means your tube's just on the way out. (they are 20+ years old now)

if you can grab a 25" Zenith tube from somewhere (most likely a CL TV), they're all pretty much interchangeable.
 
nah its not that. i have tested 3 different chassis's on this one and this is the only one that is dim. other 2 are perfect.
 
Just for if anybody searches, it ended up being the actual flyback. So now I know that flybacks can actually wear the fuck out. I thought they always either failed catasrophically (blew the fuse)... or had drifting focus/brightness. This one wore out, to where you could turn the brightness all the way up and barely see an image. It wouldn't get better and worse, just wouldn't turn up bright enough! I suspect the screen voltage was low that came out of it (that's what the knob turns anyways) but I didn't get a chance to measure it. Anways, new flyback, now it's nice and bright again.

This leads me to believe that if you have brightness problems, it could be that your flyback is 'wearing out'. Didn't think that was even possible.
 
I thought it was the tube as well. Although rare, a flyback can become weak, there's a voltage divider and capacitors inside.

flyback-transformer-focus-divider.jpg
 
Back
Top Bottom