25" WG K7000 No Picture

Zoex

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I've spent a whole day working on this thing and I don't feel like I'm and closer to fixing it. Typical 25" WG K7000 monitor, has the pincushion board, was working but needed a cap kit. I did the kit and installed a new flyback as well. Now the monitor powers up, I can hear the high voltage whine, tube generates static, but no neck glow and no picture or signs of life at all on the tube side. Turning the flyback up does not show any signs of raster. So I went to town pulling and testing parts (all out of circuit)

Horizontal output transistor checks out fine.

Fuse is fine, I don't think it's ever blown a fuse even with all the stuff I have been doing.

Diodes D18-D22 test fine.

C36 and C38 test fine.

R213 tests fine.

Voltage Regulator tests fine.

C55 tested fine, swapped with a known working one anyways.

R103 tested fine.

Swapped the flyback back to the old one that was working, no changes.

The entire time the B+ voltage has been low. The longer I hold my meter to the R301 test points the lower it drops starting around 40VDC and bottoming out around 20VDC on the unregulated side. Same thing but even less voltage on the regulated side. At some point it was giving me negative voltage on the regulated side.

I have desoldered, cleaned up, and resoldered various large resistors that are prone to bad solder joints, and checked for any obvious shorts where they should not be.

At this point I am at a loss and am thinking about trying a different tube or neck board just for the hell of it (I did swap this tube with another working K7000 as this one was going into a shooter that needed a strong tube). I'm going to make this post and go to bed, hopefully someone better than me can think of something and post it here for me to wake up to.
 
check the heater voltage at neckboard and see if you have voltage, if not that is why you will never see a picture. Also if you do have voltage, turn off monitor, wait, then check heater resistance and see if it is around a few ohms or so. if open then tube bad.
 
pins 4 and 5 on the neck board, check for 6.3VAC.

If you dont have it there follow the traces back until you do. Pin 5 is tied to ground so its easy to figure out if its bad or not. Ohm pin 5 to frame ground with the power off, should be a dead short. Theres a resistor on the neck board, check it for AC voltage to ground.
 
you have to get a flow chart or you're swimming blind

no oscilloscope and you're swimming blind but you can fix by luck and shotgunning

reflow solder joints by R101 (thinking of the tall white resistor in the little holder I think is r101 sort of in the corner) is all I got besides a

good luck
 
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R101 and R89 typically get hot enough to halo the solder. you lose R101, you lose the supply voltage to the voltage regulator. R103 is important too. the solder pads can burn up to these and you'll need to jumper from point to point to fix the circuits in such a condition.

R213 on the neckboard is for the heater circuit, commonly the solder will deteriorate here too. some neckboards will feature 2 resistors, just verify the solder is good there too.
 
I put this guy on the shelf and went on to the next one. It was doing the same thing. No way the next one has the EXACT same problem.

It was the tube.

The god damn tube.

There you have it folks, verify your test rig is not the problem before you unsolder half the parts off a deflection board.
 
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