K7000 Refurb Chassis Issues.

Hawk777th

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Hi

I just got a replacement board for my K7000 that was refurbed. My prior board had a strange rollover problem that couldnt be fixed it seemed. Also the Hcoil was non responsive to adjustment. So basically the screen was cut off about 1/4 on the right side and it rolled over backwards. I reflowed the board tried new caps etc and got nowhere.

I had an arcade tech install my new chassis. We hooked up power yoke wires dag etc. I flipped cab on and started to walk to the back to adjust my screen settings as they were somewhat off and poof, the monitor just turned off. I wondered if I had bumped a power lead or something so I power cycled the neo cab and it came right back on... only to go off about another minute later. The screen looks great when it is on, it just turns off lol.

Anyways I started searching the forums and read about B voltage so I checked it and it would seem mine is around 155V on one lead and 166v on the other. And I am guessing it is going in to HV shutdown?

I guess if I need to send the chassis back I will but wondered if you guys had any idea what would cause this.

Here is a video on youtube I made showing the problem. I show voltages on my multi meter, then go to 6:07 to see it turn off again.
http://www.youtube.com/watch?v=tS5uIsvPDBg

I have my old chassis here still to scavenge parts if I need them.

Thanks
 
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Did you try adjusting the "shutdown" pot? It's on the chassis flush mount facing up, and usually is covered in orange glue.. Clean off the glue and try turning it down..

If that's a no go, reflow solder pads everywhere.. Then if still bad, replace the regulator. It's the large tranny thing attached to the metal frame of the chassis with (2 small nuts).
 
Did you try adjusting the "shutdown" pot? It's on the chassis flush mount facing up, and usually is covered in orange glue.. Clean off the glue and try turning it down..

If that's a no go, reflow solder pads everywhere.. Then if still bad, replace the regulator. It's the large tranny thing attached to the metal frame of the chassis with (2 small nuts).

I wouldn't fiddle with the pot just yet.

To determine if it is HV shutdown, remove the chassis and lift/desolder one leg of d10 (to disable the shutdown circuit) and reinstall the chassis . Does the monitor stay on (with the high b+)? If yes, you have HV shutdown. Check C57, if good, replace the voltage regulator.

If it still shuts off with d10 lifted, your problem is elsewhere.

What was done to this chassis when it was "refurbed"?
 
New Caps Fly Back Hcoil. The line is 120-122V inside the cab.

I got it from a member here. I dont want to fool with it and wreck it I guess I will send it back.

The B voltage jumps when it goes off. The blue wire goes from 131V on to 145V when it shuts down. The red wire is 145 when on and 165+ when it goes into shut down.
 
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Adjusting VR8 will only change the parameters by which the HV shutdown circuit is activated. With high voltage, adjusting it will either shut it off sooner, or shut it off at an even higher voltage. We already know voltage is high so VR8 should be ignored.

Ceramic resistor specs not withstanding, that leaves either A. the flyback pushing volts too high or B. the voltage regulator. Start by adjusting the "screen" knob on the flyback down and darken the image. See if it shuts down after time, measure voltage. Report back.
 
Think I got it handled my yoke is really low OHM and that seems to be causing issues.
 
Doubtful. More likely that a bad solder joint occurred during shipment. Start wiggling all large parts - especially around the HOT and Width Coil - while watching underneath. ANY hint at movement should be jumpered to the next spot in the trace. Check continuity from the HOT legs and flyback pins to the next spots on their traces, too...
 
Do what he said

+++++1

It's all about solder pads.. Most monitor repair guys skip reflowing lots if not all the pads on the chassis and neck pcb.. They Just hit the obvious ones..

Doubtful. More likely that a bad solder joint occurred during shipment. Start wiggling all large parts - especially around the HOT and Width Coil - while watching underneath. ANY hint at movement should be jumpered to the next spot in the trace. Check continuity from the HOT legs and flyback pins to the next spots on their traces, too...
 
Think I got it handled my yoke is really low OHM and that seems to be causing issues.

Yoke mismatch idea could be it, but it does not explain high voltage when not under load. Even with proper yoke matching HV shutdown can occur under load because the voltage coming out of IC4 is too high to begin with, just not high enough to shut it down without load.

Reading 166v on B+ while in shutdown is a problem.

Given that the problem is intermittent seems to point towards an intermittent component failure rather than a hardware mismatch which would have predictable results. If this is the case, a properly matched yoke would only delay shutdown because draw is reduced, it does not solve the high voltage which is present without load.

If the voltage was normal without load, that'd be a different story.
 
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Its worth checking the resistor r213 on the neck board. I've found that to cause shutdown issues if its bad.
 
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