MK3 w K7197 Flyback getting hot; melting

TCinTEXAS

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I'm picking up an Ultimate MK III this weekend. Owner says it works fine, but the "little box on the monitor board gets hot and starts melting after a few minutes." I had him send me a picture, and he's pointing to the flyback.

So, obviously the flyback is bad.

My goal is to have this game working by Christmas, so I need to order a flyback (unless the new one I have for a K4900 is compatible).

My big question is, is there some other component I should address which would make the flyback overheat? If so, I'll do that, too. I plan to do a cap kit and all that, but for now, I just want it working for Christmas.

So, which flyback? Compatible with K4900 flyback? What might make the flyback overheat?

THANKS!
 
Ok, so I got the right flyback ordered, along with a HOT and a cap kit. Should be here in plenty of time.

Does anyone have anything else to add? :)
 
if the H.O.T. is not bad DO NOT replace it.

caps and flyback first!!

then if you are not up and running then we can go from there.

Peace
Buffett
 
if the H.O.T. is not bad DO NOT replace it.

caps and flyback first!!

then if you are not up and running then we can go from there.

Peace
Buffett

thank you for the HOT advice. we should probably start spamming that in every thread now.

kids, it's a transistor. either it works or it's shorted. a HOT doesn't get "worn out". I can only imagine how many people bought Bob Roberts deluxe kits and just went ahead and changed everything and wound up with a non-working monitor afterwards. it's not like a pandemic or anything, but it happens enough if you watch the monitor repair section year round.

capacitors however are guaranteed to inevitably fail. K7000s will receive tremendous results with new caps and a patented Buffett "good reflow".

make sure you snap a picture of the melting flyback though. I'm willing to bet it's a black knob OEM one. those are garbage and often crack.
 
Thank you. I included the HOT just in case. I also watched a video which said you had to desolder the HOT to remove the flyback.

If you say don't replace it, I won't replace it. Below is a picture of the chassis:

MK3-Chassis.JPG
 
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that's a nice bad flyback you have there.

do not run this monitor again until you replace it.
 
thank you for the HOT advice. we should probably start spamming that in every thread now.

kids, it's a transistor. either it works or it's shorted. a HOT doesn't get "worn out". I can only imagine how many people bought Bob Roberts deluxe kits and just went ahead and changed everything and wound up with a non-working monitor afterwards. it's not like a pandemic or anything, but it happens enough if you watch the monitor repair section year round.

capacitors however are guaranteed to inevitably fail. K7000s will receive tremendous results with new caps and a patented Buffett "good reflow".

make sure you snap a picture of the melting flyback though. I'm willing to bet it's a black knob OEM one. those are garbage and often crack.

That's what I thought, but, for instance, in a K4900 chassis, the HOT is supposed to measure .4 -.9ohms (if I recall). I had one which was measuring 4.5ohms, and someone said it was bad. It was the same model.
 
that's a nice bad flyback you have there.

do not run this monitor again until you replace it.

Yep. I figured that one out all by myself! :) The big question is why, and I think you answered it. If it's just a crap flyback, and it goes bad all by itself, I shouldn't have too much to worry about. As long as I have the chassis out, I'll go ahead and cap it, and I WON'T change the HOT.

My biggest fear was some other component frying the new flyback. I'm just learning, so this stuff is a few steps away from magic.
 
I was thinking if there would be anything else that could do that. but you consider the flyback transformer is what produces the various voltages for the chassis and powers the tube.

I know it's popular for everyone to freak out over white knob flybacks, but I've seen ONE of those fail in my 10 year journey in this business (as repair personnel; not discounting the other 20 years I've been around it :) )and probably close to 30 of the black knob variety. OEM flybacks are still superior, if you have a white knob unit that isn't crumbling or doing anything particularly goofy, just hold onto it. same with the black knob ones, you just run them until they die.

the black knob OEM ones (which probably went into circulation in the early 90s) have a pretty horrible track record in my experience. they typically crack around the adjustment pots. and the stem portion out the top where the anode comes, those tend to break off a lot. then you get arcing. same can be said for the replacements, particularly Bob Roberts. out of the 15 flybacks I've had a hand in ordering through Bob, probably half of them were either junk out of the box or wound up breaking on their own. Suzo-Happ carries their own variations of the K7000 flyback we've discovered that doesn't have the dampening mechanism built in, so you have to discharge those like a 4900 for example, and they make quite the snap.

there's a number of reputable sellers you can choose from, they're all good.
 
I was thinking if there would be anything else that could do that. but you consider the flyback transformer is what produces the various voltages for the chassis and powers the tube.

I know it's popular for everyone to freak out over white knob flybacks, but I've seen ONE of those fail in my 10 year journey in this business (as repair personnel; not discounting the other 20 years I've been around it :) )and probably close to 30 of the black knob variety. OEM flybacks are still superior, if you have a white knob unit that isn't crumbling or doing anything particularly goofy, just hold onto it. same with the black knob ones, you just run them until they die.

the black knob OEM ones (which probably went into circulation in the early 90s) have a pretty horrible track record in my experience. they typically crack around the adjustment pots. and the stem portion out the top where the anode comes, those tend to break off a lot. then you get arcing. same can be said for the replacements, particularly Bob Roberts. out of the 15 flybacks I've had a hand in ordering through Bob, probably half of them were either junk out of the box or wound up breaking on their own. Suzo-Happ carries their own variations of the K7000 flyback we've discovered that doesn't have the dampening mechanism built in, so you have to discharge those like a 4900 for example, and they make quite the snap.

there's a number of reputable sellers you can choose from, they're all good.

I ordered from security0001, because he said he could get it to me in time, and didn't charge me a premium for shipping.

I'm just looking forward to getting UMK3 up and running. My daughter and her bf love MK, and they're coming in for Christmas. Cabinet looks good, and he's got a bunch of spare parts he never got around to installing. Only has side art on one side, but no big deal. It's 300 bucks.
 
yup that fly needs to be replaced.
it is hosed.

if your H.O.T. is not shorted i would run it.

your looking for a range of .400ish- .700ish on each outer leg.
black lead to the center leg, red to the 2 outer legs.

Peace
Buffett
 
What I can see is you have a bob roberts cap kit and a new flyback. It's safe to say that kit is old and that flyback could be from a defective batch. That's what I got, cap the thing and put a new fbt on it.
 
Ok. No luck. I replaced the flyback and did a cap kit. Monitor didn't fire up. Checked the HOT; it wasn't shorted, but was measuring ~140ohms /66ohms, so I replaced it. Still no luck.

Checked B+; getting 158vdc. Pulled one leg of D10, and no luck. I guess the next step is voltage regulator. I don't have a new one, but I have another "bad" K7000 chassis. By the way, the solder side of this one is a mess.

I'm tempted to try my luck with the other chassis.

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For grins, I put the new flyback in in the "bad" chassis (The one that came with the game, but he pulled because it was bad. He didn't know what was wrong with it, but the top of the flyback was melted.) Same symptoms, except the B+ is 175vdc.

I'm going to bed. Any ideas?
 
if R101 goes out of spec it creates havoc for the B+. you should be able to measure it in circuit and find 6.8k ohm. if it doesn't reach this number like immediately, chances are R101 is bad. it doesn't matter how well it tests out of circuit, it's intended to operate in a circuit. I've discussed this with Buffett at length and I'm guessing he's never seen it or something. :p

R89 is another suspect, I think that's a ceramic. lastly, you can entertain changing out C38.

I've got a million K7000s at work doing this, I just can't fix them right now.

I did a few K7000s at Arcadecup with the same problem and replacing those parts fixed it.
 
if R101 goes out of spec it creates havoc for the B+. you should be able to measure it in circuit and find 6.8k ohm. if it doesn't reach this number like immediately, chances are R101 is bad. it doesn't matter how well it tests out of circuit, it's intended to operate in a circuit. I've discussed this with Buffett at length and I'm guessing he's never seen it or something. :p

R89 is another suspect, I think that's a ceramic. lastly, you can entertain changing out C38.

I've got a million K7000s at work doing this, I just can't fix them right now.

I did a few K7000s at Arcadecup with the same problem and replacing those parts fixed it.

Ok, thanks. I've got a working K7000 coming from Buffet to get me through Christmas. I promised the family UMK3 would be up and running. Stupid me!!!

I'll probably tackle this after Christmas, but you've given me what sounds like very helpful information. Thanks.
 
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