K7000 Help. B+ = 165V

ajcrm125

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Working on a K7000 these past few days with no high voltage.
I did a cap kit, replaced the flyback and voltage regulator. I then noticed that the B+ was 165v and the voltage after the rectifier was 170v.

???

Any idea how I'm getting 170V at the output of the rectifier with only 120v going in? Is the HV circuity feeding back into it?
 
Mark explained the math which yields the 170v (thanks Mark!).

So now it's just a question as to what's causing the 165v at the output of the regulator.
 
Same here!

I'll be working on a chassis with the same issue tonight. If you don't hear anything and I find something, I'll let you know.

The troubleshooting guide for this monitor says to check C36 too, as well as the VR. If you did the VR already, and it's not C36, then we're in the same boat!

Like I said, I'll let you know if I find the issue with mine.
 
Yeah I replaced the HOT too.. no dice. Still crazy high voltage for B+.
Really want to get this chassis working for Thanksgiving party.
 
Hopefully I find something

I'll let you know.


If anyone else has anything that points to a B+ spike, jump in!

I haven't tested the voltage at the big resistor on the side yet while powered on. I will do that later if I can. The machine is over at my buddy's house, I just have the chassis.
 
My VR was good

I just pulled and tested the VR that was in there and it tested good. I suspect that I'll still have 165V B+ if I try the chassis again.

There are three of us now that have this problem, and all recently after flyback replacements.

I got mine from Bob Roberts. I am not saying necessarily that we all got bad flybacks (though possible) but maybe if we all have the same chassis, there's something else that this new flyback doesn't like.

Where'd you get yours from?
 
Well its working now. I had it in the lab with just the anode connected to an old 19" tube I had laying around. I really didn't feel like lugging the 25" in tube down there.

I looked more closely at the schematic and it appeared that the yoke coils fed into the shutdown circuitry as well. Brought the chassis upstairs and installed it fully back into the game and she came to life.

Since I replaced just about everything I'm not sure what caused it to come back to life since shew was originally dead but she's good to go now.

Xmen lives!!!
:)
 
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I just pulled and tested the VR that was in there and it tested good. I suspect that I'll still have 165V B+ if I try the chassis again.

There are three of us now that have this problem, and all recently after flyback replacements.

I got mine from Bob Roberts. I am not saying necessarily that we all got bad flybacks (though possible) but maybe if we all have the same chassis, there's something else that this new flyback doesn't like.

Where'd you get yours from?

I got the K7000 kit from bob (new caps, flyback, VR and HOT)
 
What do you mean?

By the yoke coils fed into the shutdown circuitry?

I have a 19" tube that I'm plugging into. What would be different that would cause shutdown from the yoke?

Sorry, but this has been driving me nuts, as I think that I've gone over everything I could and I just don't understand what's going wrong with this.

I mentioned another person, Sochx, with the same problem. That's a long thread, and before I start one that might be long like that, maybe it's simpler.

Thanks in advance.
 
The K7000 will not give proper B+ if the yoke wires are not plugged into the chassis, even if it is working properly. Actually, if you have your meter on it when you first turn it on, you may get a proper B+ for a second, then you'll hear a tiny click and it jumps to +145 or +160. Once you hook it up to the proper tube and yoke, then it will attempt to power up fully, which will blow the HOT or fuse if you still have a problem with that.

I often bench test K7000's without a tube (as the HV section will not power up without the yoke connected) until I can get no blowing fuses or other parts and a B+ of 145-160; Once I have that, then I'll throw it on the tube to see if it's good. It also helps to have an extra tube lying out so I can set it up on the table next to the bench and test right there with my test rig/JAMMA board before I lug it off to a cabinet...
 
BTW - if you have replaced all the parts (including flyback), R103, R89, and R101 are good, C36 is the proper 612/.0061 capacitor, and you still have a B+ of 160, then you are about 95% likely to have a trace/pad problem somewhere in the section around the horizontal width coil or behind the flyback.

There is a 5% chance that your "measured as good" VR is actually bad, especially if you haven't replaced it yet. I don't see that very often, but I have seen it. It measures as good with the meter, but then doesn't rectify properly under load....
 
Wow, great info!

I appreciate the response. I did replace it even though it tested good, but didn't get over to my friend's house where the cabinet is.

I'll go over the traces in that area and make sure everything's good.

Although the HOT checked OK, I have a spare, so I'll put that in too for good measure.

Also, just for informational purposes:

I got it and it was arcing all over the place

Had the white knob flyback - replaced it.

Powered on and got shutdown. Initial HV "crackle" then nothing.

Fuse good.

Replaced c36

Went over most solder

Did the cap kit

checked neckboard for B+ and it's 165 + or - a volt or two

touched up more solder to ensure there was no bridging

replaced VR and will do the HOT tonight too.

Will post if this works (or doesn't) tomorrow!
 
Wait, some of you guys are trying to test K7000 chassis WITHOUT the yoke plugged in and your wondering why it doesnt work?

That yoke is not only an integral part of the circuitry but its a big part of the "load" that I've been referring to in other threads. With that yoke missing your VR is going to go nuts and run high.

After considering things your all very lucky that other parts of the board didnt blow up.

I used to keep spare yokes around for testing monitor chassis. I had a burned to all hell GO7 that I'd use and just put the right yoke on it for the chassis I was testing.
 
If the chassis is functioning properly, nothing will burn up if the yoke isn't connected. It just won't activate the HV section.

Older monitor like the K4900, though, WILL power up fully with the yoke disconnected, so you have to make sure the anode cup is isolated (glass jar works great) before attempting that.

Just wait until you get to those monitors that won't power up properly until you have the degauss wire plugged in... :D
 
I my case I didn't have the yoke plugged in. Since there was no load on the regulator it climbed up past 160v. Plugged the yoke in and it's now fine.
 
My question is though..

If I am getting a reading of .7 ohms (reads shorted to me) on the red and blue yoke connector, would it be like not plugging anything in?

I have the same symptoms, and just don't want to be chasing the chassis if it's not that.

Would a rotted yoke cause a voltage spike and put the monitor into shutdown?
 
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