common k7000 issues - common repairs

How can I test R105 for the degaussing coil? I don't hear the "sound" of the degaussing when I power up and I wonder if it is not working well. I measured the voltage to the coil and it appears to reach about 50V for less than a second. I was using a DMM where I fixed the range so I could get a reading as quickly as possible.

My PTC is kind of cracked open and very hot to touch ;)

It's a thermistor. It's normal for it to run hot. It can even burn a 'shadow' against the side of R104. When it's nice and cool, measure it like any other resistor. It should read around 7.5 ohms in circuit. You also want to verify the solder joints are good because they can crack and oxidize from how hot it gets.
 
Got a K7000 with fluctuating/unstable/incorrect B+? Don't overlook the easy things...
 

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Got a K7000 with fluctuating/unstable/incorrect B+? Don't overlook the easy things...

Just went through this exact thing rebuilding a Medium Res k7000.. But I caught it in the rework/rebuild process. I removed and re flowed just about every single component on that board. (basically just skipped the color inputs). It's prompted me to just started doing that work regardless now. Can't hurt.
 
Already have a thread started on this, but figured it should go in here as well for historical purposes if it gets figured out…

Trying to get a K7000 that I had for some time up and running for a U5000 tube I picked up. It powered the monitor up but was getting 157VDC and a had white screen. I since recapped it (including filter), reflowed header pins and replaced IC4, Q4, Q7. The voltage is now at 129.2 VDC but but still getting a white image (more of a bar with additional lines below). I thought it might have been a sync issue, hence replacing Q4 and Q7, but no changes. I started a thread that includes a picture of the screen. I'm out of ideas and not sure what direction to go in. Any help is greatly appreciated.

BD8SQ6.jpg
 
Read this thread:

 
I don't believe I am getting vertical collapse because there is no image…just a solid white bar.
 
Yeah. You've got a vertical deflection issue it seems. Get that fixed first and then worry about it being all white.
 
Working on another 7000 today. Came across the most common issue on them and wanted to post for reference. Inspection is key. Not just testing components for their correct values, but R101 and R89 run hot and they quite literally 'bake' their solder joints. The pads oxidize so severely that the solder joints lifts right of the pad. Case in point: got this in for repair I always remove R89 and R101 in order to clean up and fix the pads. As with almost all of these K7000s, both pads for R101 were oxidized and the upper pad for R89 that is shared with R101 was really bad. The whole joint had popped off.

Using my sanding pen, I removed the oxidation, reinstalled the resistors, and bridged the joints to allow for better connection and to act as a rudimentary heat sink. This is mandatory on all K7000s if you get/need to work on one. I need to go through and finish the reflow on everything else and finish up the rebuild, but just wanted to reiterate this issue for those unfamiliar. This is also an good example of what "reflow" actually means. People think "reflowing" a joint means that you simply heat up the existing solder or add new solder to the existing joint. Technically, reflowing is completely removing all the existing/old solder and adding fresh/new solder to the component/pad as shown here. It's a misnomer. Just wanted to put that our there too. Thanks.

Here's a link to the sanding pen I use... https://www.amazon.com/Prep-Pen-FBA..._bap_d_grid_rp_0_1_ec_pd_gwd_bag_pd_gw_rp_1_i
 

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The chassis above ended up working after the rework on the joints, but the B+ was only around 100v instead of the proper 130v. Turning the G2 voltage up would make it dip down to around 80v. Turns out the voltage regulator was failing under load. The B+ resistor was reading the proper 180 ohms, the regulator was reading correctly in diode mode on the meter, all readings were correct but under load, it was failing. Replaced it with a new one and B+ was back to 130v. Haven't had this issue in a while so I wanted to document it.
 

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Just a data point to add to the thread. Was fighting a "jail bars" issue on a K7000:

Changed out C56, C57 on main board (B+ regulator circuit) to low ESR caps - no change. Also saw no change in ripple voltage on B+.
Changed C204 on neck board to low ESR 4.7uF - no change
Changed the flyback - RESOLVED!
 
Got another K7000 across the bench that was blowing fuses. The HOT was shorted but I couldn't find any failed components or outward causes that would explain it. I did find a cracked solder joint on one of the flyback pins that was going straight to the HOT collector, so I assume that was the cause. Reflowed everything, capped it, replaced the HOT and the fuse, and it's running great.

 
I have a question about my K7901. I did a recap on it and everything was working, B+ 122.6 VDC, but it took about 10 minutes to come into focus. I put a new flyback in it, which didn't make a difference on the focus warmup. I then started having issues with a lot of arcing on the back of the tube between the center coating with the anode cup and the aquadag. This would result in the image jumping momentarily. I added a wire braid to contact the aquadag and grounded it with the neck ground, and cleaned the anode cup, with no reduction in the arcing. (Note that the video is during power on, but it would arc randomly during gameplay).


Next I put the original flyback back in, and now the image is dull with flyback screen, brightness, and contrast all the way up. Also, when I turn the flyback screen pot all the way up I don't get the white retrace lines. Image also has some blooming, especially with the red...pots won't adjust it out. However, I'm not getting the arcing anymore.

Any thoughts on what my problem could be?
 
Turn down the room lights, that will give you a better idea where the HV is leaking.
 
I did that and never could see the source. It just looked like it was jumping from the center coating to the aquadag on the sides. I really think that new flyback was suspect.

I'm past that issue however, I'm trying to figure out now why my brightness is reduced and the imagery is not as crisp as it was.
 
If that arcing (for whatever reason) inside the neck was boiling off the cathode coating you may now be getting reduced emissions from the crt. You would need to put the crt on a rejuvenator to see what the emissions are like.
 
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K7000 in for repair. Blowing the fuse. All components check good. Nothing is reading incorrectly or is bad...yet it still blows the fuse. Flyback was replaced. Same issue. When all else fails, check the HOT insulator. In this case...bingo. I'm pretty sure the thermal paste that the owner used is conductive and was arcing through the insulator to the frame, taking out the fuse. The HOT itself was still good. Also looks like someone was scraping away at the frame for some reason. Not sure why. I checked for burrs and anything else that could pole through the insulator and didn't find anything. Pretty sure it was the paste that was conductive. Removed all the thermal paste, installed a plastic insulator as well as a thermal one, re-secured the HOT, and fired it up.

Success. I didn't have any spare fuses (ordered some and they'll be here tomorrow), so for now I used my 2a circuit breaker. It powered right up and after a few adjustments, it's running perfectly, Still need to full cap it and do all the rework to it that I normally do, then it will be good to go. Just wanted to remind everyone not to overlook the non-usual causes and you don't need to use thermal paste at all on the HOT or the voltage regulator. Wells used almost no paste themselves from the factory and the heat sinks provide more than enough heat transfer. These have been running for 40 years with dried out factory paste and it hasn't caused any issues so far (my opinion of course).
 

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It's common enough now when I go through a new to me k7000 I always pull the HOT for a lightbulb test and re-paste it. I've made the same mistake in the past with CPU thermal compound.
 
So I decided to swap the tube with a donor Sanyo TV that I had. The tube swap went fine, I think. I kept the old flyback in it and the image was still dull even with screen, brightness, and contrast all the way up. No retrace lines are visible with the screen turned all the way up. Same symptoms as before, so I guess it's a chassis issue. I found the horizontal width coil was out of circuit, reflow didn't change anything. Put new flyback in, same exact symptoms. At least now there's no arcing.

Image is displaying, it's just dull, out of focus, and mostly distorted.
 
So I decided to swap the tube with a donor Sanyo TV that I had. The tube swap went fine, I think. I kept the old flyback in it and the image was still dull even with screen, brightness, and contrast all the way up. No retrace lines are visible with the screen turned all the way up. Same symptoms as before, so I guess it's a chassis issue. I found the horizontal width coil was out of circuit, reflow didn't change anything. Put new flyback in, same exact symptoms. At least now there's no arcing.

Image is displaying, it's just dull, out of focus, and mostly distorted.
Are your G2 and focus wires connected backwards?
 
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