K7000 Post Cap Kit - HOT Lighting Up ***w/ VIDEO***

Michael Roma

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K7000 Post Cap Kit - HOT Lighting Up ***w/ VIDEO***

I just capped and replaced the HOT and flyback on a 25" K7000. Upon initial power up the monitor worked great. The game was on for 5 or so minutes without issue and while I was in the middle of adjusting the colors (fiddling with the red cut off pot on the neckboard) the image died. I heard a crackle and immediately turned off the game.

I pulled the chassis and tested the fuse (GOOD), HOT (GOOD, not shorted). See video below for what I am talking about.

http://home.comcast.net/~mtpacifico/_KLOV/K7000/K70002.htm

Any suggestions???

- Mike
 
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Cold solder joint? Voltage regulator bad?

With your high voltage probe, do get a steady voltage of approx 20,000 volts? Or does it swing up to 30,000 and drop to zero?
 
Ken, in his video there was actual arching from the HOT to the heatsink.....

I'd check that the mica insulator is intact between the HOT and the heatsink first.
Then I'd measure the B+ to see what it is doing if it is still shutting down.
 
Yep. A quick spark right behind the HOT.

Okay, here are the things to check:

1) Mica insulator present behind HOT and with no rips.

2) The middle leg that is bent backwards under the metal wall to the hole isn't too close to the metal (usually the insulator extends down far enough to keep this from happening).

3) you didn't use a heat sink compound that is conductive.

4) You didn't forget to connect the ground wire from the tube to the neckboard.
 
1. There were two mica insulators in between the HOT and the heatsink (see pics below). I cleaned them off and they look to be in OK shape w/o cracks or tears.

2. The middle leg did not appear to be touching the heatsink. I bent it down further just to be sure.

3. I used Arctic Silver 5. Their website says that it is NOT electrically conductive. I do have some TC-1996. Can't find anything saying that this is or is not electrically conductive. Will this work?

4. I did remember to connect the ground wire from tube to neckboard.

The HOT arcs immediately upon powering the game on and continues until I power the game down. I don't want to leave the game on to check B+ while the HOT is arcing to prevent damage to other components.

- Mike

mica.jpg


HOT.jpg



chassis.jpg
 
3. I used Arctic Silver 5. Their website says that it is NOT electrically conductive. I do have some TC-1996. Can't find anything saying that this is or is not electrically conductive. Will this work?

Made with 99% pure silver. I'd say that's a pretty high percentage of being your problem.
 
Made with 99% pure silver. I'd say that's a pretty high percentage of being your problem.

It's not really conductive, but it IS capacitive, so it would build up a charge, discharge, then repeat. I'd get it all off...
 
Use the Radio Shack silicone heat sink grease. It's what I use.

Also, be sure the transistor's mounting screw goes through a small white plastic bushing. This insulates the screw from the frame too. It should already be there.
 
Use the Radio Shack silicone heat sink grease. It's what I use.

Also, be sure the transistor's mounting screw goes through a small white plastic bushing. This insulates the screw from the frame too. It should already be there.

Ditto on the grease for me...

Good transistor parts suppliers, supply new nylon bushings and insulator with the replacements, i.e. NTE.
 
you don't get mylar caps when you do a cap kit....and there are two or three right behind the hot area that should be checked for short. Just set your meter to the ohms scale and check the big blue mylars sitting right there. I've seen the big one shorted a couple times with this chassis. Check C36, it sits across the Hot output.
 
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I tested the caps behind the HOT and they all test good, not shorted.

I will pick up some silicone heat sink grease at RS as Ken suggested and try that.

Thanks for the suggestions thus far and I will post results.

- Mike
 
I picked up some silicone thermal grease and used that in lieu of the Arctic Silver 5. I checked the VR, HOT, and mylar caps again (all checked good). I powered it on and it sparked again. I immediately powered down and cussed a little. Then I decided to pull the HOT's mounting screw and try without it.

And wouldn't you know...

k7000fix.jpg


Now to order some nylon screws and nuts...

Thanks to everyone and all their assistance. I hope this can help someone in the future.

- Mike
 
Also, be sure the transistor's mounting screw goes through a small white plastic bushing. This insulates the screw from the frame too. It should already be there.

Ken mentioned this early on....it might have fallen out when you replaced the HOT.
It would have been in the hole in the heatsink that the screw goes through.

Try looking at an ACE hardware or somewhere similar and see what they have in their nick nack drawers for spacers and nylon screws and such. (not sure if they will have anything that small though)
 
I picked up some nylon screws and nuts at Home Depot and secured the HOT with them. I powered the game up and smoke started coming from the HOT/screw area.

I have capped a couple K7000s in the past and have never seen one with a plastic bushing for the HOT mounting screw. I have three other K7000 chassises here. I checked the screws on those and none of them have the bushing.

Anyhow, I started thinking that perhaps the new HOT I used to replace the old one with was faulty. I desoldered it and when I went to remove it from the PCB the legs just fell off. I tested and soldered the old HOT in, mounted it with the nylon screw and the game has been running fine on my test bench for 45+ minutes.

- Mike
 
are you sure you are using the correct hot? does your mylar insulator have any holes or metal in it?

The hot itself should be encapsulated so you cant accidentally ground it out with a screw. If you have a bare metal tab on top instead of a full plastic jacket, it aint right.

Unless this is some odd version that uses some odd hot. Post some pics man. this might make its way to the k7000 sticky.


edit saw pics again, looks like the correct hot. at this point id reclean everything thuroghly then replace the mics insulator and add a nice coating of virgin silicone paste.

The screw hole on both of those insulators is too big. The hole SHOULD be the same diameter as the screw only. With those insulators the screw hole is so big id assume your getting arcing from the metal on the back of the hot closest to the screw hole to the metal frame.
 
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I should mention that I recently ran across a K7000 new flyback that kept blowing HOTs. Put the old flyback back in and it didn't (although it had other issues which is why I replaced it in the first place. Got another new flyback and everything was fine.

Of course, I lost 5 HOT's because the flyback was "new" and tested okay with the ring tester...
 
yeah i wish we could make some sort of robust hot simulator so you could test with that untill you got it right them put a hot in.
 
Just sharing my nearly identical experience of a sparking Q11 D1398 HOT. I was new to the K7000 board and mine came with a metal screw on the Q11 HOT but no bushing. Unfortunately I only found this post much later after I fixed the problem as I apparently I was not using the right search words (sparking, shorting, sparks).

I tried the following things (see pics below), which all failed:
- 4-40 nylon screw,
- using heatshrink to insulate the metal screw
- cutting off small metal shavings from the mating hole
- two different thermal pastes (including the "non-conductive" ARTIC MX-4)

Problem finally got fixed by simply using standard white thermal paste from arcadepartsandrepair. Note that their 6-32 nylon screw (MP1036) is fine, but their nylon nut (MP1035) which is "self-threading" is useless as it takes too much force to screw it in (if you are lucky) and it will never unscrew. A metal nut works fine since the nut is on the grounded heatsink side anyway. Happy to report that it's been working fine for the last couple of weeks now.

In summary:
- 6-32 nylon screw (unless you have the smaller 4-40 metal screw with the nylon bushing but mine was missing)
- use the mica insulator (which I always did)
- white thermal paste available [here]

And here are my pics of what failed and the resulting damage for your enjoyment. :)

1 - Q11 spark.jpg2 - Q11 Damaged.jpg3 - nylon screw.jpg4 - smooth hole.jpg5 - heatshrink sleeve.jpg6 - heatshrink sleeve mounted.jpg
 
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