K7000 Blew Up!

zenomorp

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Hey everyone. Just wanted to share my experience with my stupidity. I recently purchased a used, working K7000 series 25" monitor chassis from a nice guy here at KLOV. I used it for testing for couple days and it worked great. Only thing was that the tube I was using has no isolation for the chassis. You know, the white insert towards the front of the frame and the little isolation stand off pegs at the back of it for the chassis to sit on. So I just grabbed a magazine, layed it in the frame, set the chassis on it, and it worked fine. Couple days ago, while it was on, I tried to disconnect the video cable, the chassis shifted, and the bottom corner arc welded to the frame. BIG flash of light and the monitor of course shut off. I was PISSED! I can't believe I did that. So I removed the chassis and got to troubleshooting. Checked the HOT first. It was good. Checked the IC4. It was good. Next came the 4 diodes for the power circuit. ALL 4 read shorted. I removed them from the circuit and they all still read shorted. I just happened to have an extra non-working K7000 19" chassis laying around and stole the diodes from it. Installed them on the other chassis. Read them just to be sure, and they read fine. (.542 one way and 0.L the other). Reinstalled the chassis on the tube, turned it on and.....voila! Monitor came back on and works great. The moral of the story is, DON'T mess with stuff while power is on! I knew that, but I had a lapse in judgment. I hope you can all forgive me and learn from my mistake. Thanks for your time.
 
you're not the first one to do something like that.

i had a replacement old-style large Defender audio board hooked up in my cab for testing, but the mount is for a newer small board so it was kinda half hung by a zip tie from one of the screw holes.

turning around to push in the interlock i bumped the audio board and POP! i lost power. it had shorted to the mounting plate, frying the brand new switching power supply i'd just installed not ten minutes earlier.

so what did i do? surely i didn't secure the audio board properly but went and replaced the PS with another brand new PS which, less than five minutes later, was dead from me doing the same thing.

at that point i did break out some PCB legs and got the audio board mounted and put in a not brand new but functioning switcher which still works to this day even though it's been ejected from Defender in favor of a rebuilt original.

the dead ones i handed off to a KLOVer who fixed 'em right up.
 
I had a 25" K7000 blow up inside a KI2 cab. It made a crack so loud I thought for sure it was going to catch fire. Chad at Arcade Cup fixed me up, good as new.
 
You must have missed my thread entitled "How to be a dumbass in one easy step" where something similar happened to me...
 
You must have missed my thread entitled "How to be a dumbass in one easy step" where something similar happened to me...

+1. I've done that exact same thing... except I sold the game, they came to pick it up, and when I cap kitted the monitor, I forgot to screw the chassis back down. It worked just fine where it was sitting, we took it outside, they wanted to make sure it still worked (after getting it through the door), and BLAM! I pulled the back off and saw the chassis laying there. I pulled the chassis, found the fuse blown and those diodes shorted. Luckily, like you, I had a spare 19" parts chassis laying around that I swapped the diodes on.

Unfortunately, it probably won't be the last time I make that same mistake :p .

DogP
 
I've had some machines where I didn't have the chassis tightened down all the way. had a U5000 with that plastic trim piece in the front completely fallen off. how it didn't get fried I'll never know. (this is actually my "good" U5000 I speak of)

had a couple setups where I didn't have the screws for the tray. got the tray held on with zip ties and the chassis held in place with some spare wire I had laying around.

interesting read, I was reading Randy Fromm's Blue Book... did you know you can swap a 7000 chassis onto a U5000 tube?? even he's baffled, but there's a guy that he knows that's done that multiple times and it worked.
 
I've seen your youtube videos of this project you're working on. From the most recent one it looks like you are powering the monitor by pugging it directly into that power strip? A K7000 series monitor chassis needs to be powered with an isolation transformer. I've heard of k7000 chassis running without one for a while and I've heard of them blowing up immediately. I don't know why some would run for a while and some would blow up right away, but I personally wouldn't take the chance.
 
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I've seen your youtube videos of this project you're working on. From the most recent one it looks like you are powering the monitor by pugging it directly into that power strip? A K7000 series monitor chassis needs to be powered with an isolation transformer. I've heard of k7000 chassis running without one for a while and I've heard of them blowing up immediately. I don't know why some would run for a while and some would blow up right away, but I personally wouldn't take the chance.

Thanks for the info. I've had a K7000 in my MK1 for nearly 2 years with no isolation transformer and it has never given me any problems.
 
Thanks for the info. I've had a K7000 in my MK1 for nearly 2 years with no isolation transformer and it has never given me any problems.
Interesting. I'm not sure what factors would play into how long a monitor can run without an iso. If it's a dedicated MK it should have a large transformer as part of that assembly that mounts to the bottom of the cabinet. Looking at the manual, that large transformer provides isolated power to the monitor as well power to other things such as the marquee light.
 
A K7000 DEFINITELY needs an isolation transformer... it's dangerous to run it without one, even if it doesn't blow up. If it works, your monitor frame is likely not grounded (which is why it doesn't blow), and running hot right now (if you touch it, you could get shocked). I'd HIGHLY recommend putting in an isolation transformer.

DogP
 
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