K7500 tube swap problems

mecha

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I have a K7500 (from a Blitz '99) with a Zenith tube that was rejuved 3 years ago that didn't hold out for very long.. went back to the shorted red and dim green. last month I found a 25" Samsung at the end of the driveway at one of my neighbor's houses and figured "our Carnevil's got a K7500 with a Samsung tube" so I gave it a whirl..

the tube numbers didn't match up, but they both started with A63, and the yoke readings were about an ohm off each way.

Zenith: hor. 1.0 ohm / ver. 7.5 ohm vs.
Samsung: hor. 1.8 ohm / ver. 6.5 ohm

I figured that was close enough (from what I've read in other threads), but given it's a medium resolution chassis, I think I had to do the yoke swap regardless. so I did that, and kept the Samsung rings. (as per what I've read everywhere..)

I'm going to assume the CRT neck pinouts are the same cause I didn't blow anything up and I'm getting a white/grey picture (had to turn the G2 up high to get any real picture). you'll see in my picture that there's a chunk of the left side that's black. the yokes, oddly enough, look virtually identical, and I placed the K7500 yoke in the exact same spot the old one was, and the rings I marked with a sharpie before I pulled them to put the K7500 yoke on.

if anyone has a logical explanation for why this happened, or even better yet, knows what I can do to fix it, I would appreciate it!
 

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First, never assume that the neck pinouts are the same. Use the B & K Rejuve Guide to see if the two tubes use the same adapter.

Second, the 7500 is medium res, a TV is standard. So, the TV yoke won't work. You'll have to swap it.
 
Peale said:
First, never assume that the neck pinouts are the same. Use the B & K Rejuve Guide to see if the two tubes use the same adapter.

point well made. I tried searching tube numbers on my phone, that's incredibly difficult.. I guess I got lucky this time.

Peale said:
Second, the 7500 is medium res, a TV is standard. So, the TV yoke won't work. You'll have to swap it.

I acknowledged that you have to swap the yoke no matter what with medium res.

mecha said:
I figured that was close enough (from what I've read in other threads), but given it's a medium resolution chassis, I think I had to do the yoke swap regardless. so I did that, and kept the Samsung rings. (as per what I've read everywhere..)

I tried tightening the yoke up against the tube as far as I could. I could try going back with it. that little bit of movement should have had some kind of effect right? also, since I'm using the same yoke with the chassis there's no danger of me toasting it yeah?

that's really all I got for now.
 
I was just messing around on google last night and discovered that if you don't wrap that one wire around the core of the flyback correctly, you lose half the screen. why nobody here mentioned that, whatever. :)

I got it to work. tube's installed on the K7500 frame and all. the blue pot went a little flaky, and the joystick board isn't working right, so I can't get it to a crosshatch pattern to do some more convergence work, though I'm probably 98% there, hard as the rings were to turn, I somehow turned them a little bit, and I'm afraid to get too aggressive with them or else I'll break them.. so I might just leave it.

white balance was relatively close, I'll have to re-adjust all that too since this chassis was mated to a really jacked up tube before.

all in all, thanks everyone.

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can you show a pic of what wire you put around the flyback in case somebody else has the same problem.
 
So, all you did was wrap that wire around the flyback ?

Yeah seriously imagine that shit lol.

I put the monitor back in the cab for now but have to pull it to fix the blue bias pot, I'll grab a pic then.
 
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notice the part I'm holding up, that goes over the wired end that connects below the flyback. I'm not sure if that makes a difference, but considering this stupid wire makes any difference at all, it might lol (got this from an extra parts chassis that still had the original ziptie around that wire I cut off so I could show the placement better)

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The black wire on k7500s is always looped around the core (flyback). Issues I've had with that wire is when I replaced the fly.. I kept the wire in the same place it was originally but half the screen was missing or dark bar.. What I finally figured out was to not solder one end down and use an alligator clip.. Loop it in different ways till you get a perfect pic.. Man, what a pain in the ass to figure out on your own.. The WG flow chart points out this wire also..
 
i would put the wire tie back on so that it does not move around and makes the turn that is required for the image to look rite.

that is just my opinion on what i would do.

Peace
Buffett
 
I wish someone could explain this wire's significance heh

I don't know if the over/under makes a difference, but the direction you feed the wire in around the core does. the one pictured is just an extra, I don't even have a remote or a neckboard for it.
 
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