K7000 - Medium Resolution Questions

DanV

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I have a few questions about the medium resolution variant of the K7000.

First, a customer had me repair a 19K7000 in his APB machine. Since the chassis had a white knob flyback, I replaced it while it was out. Between the flyback, trace repair, and caps, the monitor now fired up with a nice looking picture.

However, after about 30 seconds, the screen went blank, and then about 5 seconds after the screen went blank, I heard the loud "snap" and could smell burning electrical components. The new flyback had completely split in two. It has a horizontal crack in the center that left a clean break all the way around. The break was so clean that I thought I must have gotten a defective new flyback.

First question, does the medium resolution K7000 variant use the same flyback as the standard resolution version? I assumed it does since I was under the impression that the medium resolution variant was just a normal K7000 with a few hacks. But I want to make sure before I start blowing up a whole bunch of new flybacks trying to find the issue.

Next question, I repaired a different 19K7000 (std. res) and put it in the APB so that I wouldn't have to keep the customer waiting (this is actually how I discovered APB was a medium resolution game – stupid me). Needless to say, I was puzzled at first by the double image. I eventually gave up and went home, looked up the APB manual and discovered the problem. So now I have a non-working medium resolution K7000 and a working standard resolution K7000. Pardon me if this question is stupid, but is there a way I can take parts from the non-working medium resolution K7000 to make the working monitor into a medium resolution? I could easily move the satellite board, the capacitor on the foil-side of the chassis and copy the jumper modifications, but would this make a medium resolution K7000 or would it make a non-working K7000?

Finally, there was some sort of modification on the neck board, I believe it was jumping one of the neck pins to somewhere else on the neck board. If it's a common factory modification, it was a grey wire, about 4" long, if not, disregard that information. Whatever it was, it fell off the neck board after the flyback exploded. Does someone have a medium resolution K7000 they can look at and let me know the modifications to the neck board? Maybe a couple pictures?

The parts that blew when the flyback went:

- Fuse popped
- C57 shorted (is that normal when a flyback goes?)
- C36
- IC4
- HOT
- R103 reads a dead short – I thought it would go open?
- Haven't repaired it yet to test, but I'd imagine IC2 is bad as well
- Probably others I'll find, all the HV diodes tested fine, and there doesn't seem to be any additional burnt traces

If I can't modify the working K7000 to be medium resolution, I'll repair the non-working medium resolution chassis. Does anyone know if all the above components are the same between the two chassis? The both have the same voltage regulator, which is fortunate. I'm worried that I need a different oscillator to match the medium resolution frequency?

I appreciate any input or advice.
 
1) Yes, they use the same flyback.

2) Not really. There are a lot of differences, and it would be easier to repair the bad one. Swap the flyback from the standard to the medium, replace the other bad parts, and see what's up.

3) That's not typical. Sounds like someone was worried about a connection and added a jumper. Visually inspect the neckboard for cracks or bad traces and add any jumper as necessary, and don't if there are no reasons to.

As for "why" this happened, did you remember to connect the dag wire? This is the black wire from the corner of the tube that connects to either ground on a corner of the neckboard or to the side-wall frame of the chassis. If this wire is not connected when you power up, it causes electricity to arc from multiple places on the chassis to the frame, and will eventually blow up parts on the chassis...
 
Thanks Mod,

I considered that it could have been a lack of grounding. The dag wire was connected, but the tube was so dirty that I wondered if maybe there was no connection between the ground strip on the tube and the aquadag? I cleaned the tube the second time I came just in case. I've also added an additional ground wire from the neckboard to the monitor frame.

I guess I'll be repairing the med resolution chassis. Is IC2 the same between the two variants? Maybe I'll be lucky and I'll be able to take all the bad parts from the working K7000.

Thanks.

mcandrewsoun, C38 still tests fine.
 
wow cool(but not for you) take a pic of this failure if you get time please...

I had a new k7000 fly also die after about 2 years(but only 20 hours use mabye)
 
use 053X0528-001 OR 053X0641-001 flyback as a replacement.
the medium rez is probably about 25 - 40% harder to fix than the standard rez versions due to the almost inevitable trace rot and resistor corrosion due to extreme and harder run time. Also, some that i get in have factory jumpers removed that are needed or the wrong components put in place due to confusion with the standard rez construction.
 
Thanks for the tip, Chad. I'll look at the model numbers of my extra flybacks to see if I have one that matches. I'm assuming I can buy one off you if I don't? :)

The monitor was running perfectly for about 30 seconds with the new flyback before it blew up, and had been running for over a decade before it needed repair this time. So all the components on it should be correct (although, not necessarily still in value). I'll take my time and make sure all the components are in spec, and that all the traces are still intact.
 
After I pulled the flyback, the VR and C57 now test fine. So I'm guessing when the flyback blew it shorted to ground, making lots of things test bad in circuit.

After retesting:

HOT is shorted
C36 is shorted

Looks like the VR is actually good, which is odd for a flyback blowout.
The replacement flyback I had put in was a 053x-0528-001, so it wasn't the wrong flyback.

I'm thinking the failure was caused by either poor connection to ground, a bad new flyback, or C36 going bad and the flyback burning up. But before I rebuild and throw it in a machine again, does anyone have any ideas on something else that could have failed in the circuit, and possibly overdriven the flyback causing it to fail? I just want to cover all my bases.
 
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