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Author Topic: Mismatching tube issue  (Read 1315 times)

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Vilepickle

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Mismatching tube issue
« on: October 05, 2015, 02:22:02 pm »
I repaired a 25" k7000 chassis board recently. In another 25" machine, I decided to try the chassis since its chassis was also a k7000, or one that looked almost identical. It worked for a little while, but I definitely had arcing inside the tube so I think the tube was a mismatch for this particular chassis.

My question is... what typically blows out if you get too much arcing like this in a tube mismatch situation? I definitely blew something out but I'm not sure what it was. I've replaced the flyback, C36, D18, HOT, and IC4 since but it's still not coming back to the state I had it. The HOT, IC4, and D18 definitely didn't read right. I did a cap kit right before it blew so it's also possible I need to re-cap kit.

qrz

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Re: Mismatching tube issue
« Reply #1 on: October 05, 2015, 07:02:07 pm »
there shouldn't be ANY arcing  in or outside the tube.

likely a neck fracture allowing loss of vacuum.


with any luck, the spark gaps did their job and didn't allow damage to cathode drive circuitry (video)

a hard arc can cause a Hout xistor short. which, in turn , may overload the power supply producing damage there.

most modern SMPS units will go into a protection mode during a high current condition averting serious supply damage


Vilepickle

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Re: Mismatching tube issue
« Reply #2 on: October 05, 2015, 11:33:35 pm »
By power supply do you mean the actual cabinet power supply? The cab this happened in is running fine after I fixed its normal chassis now.  The chassis that blew is still not working but I was going to replace many of the diodes in the early circuit soon as the next thing.

When I first blew it, I replaced the HOT only. I heard a brief second of high voltage starting to happen and then it stopped. Perhaps I blew the HOT again? Since then I've done those other components and a few were indeed not reading correctly. But it is still blowing fuses.

I've heard about the high voltage shutdown due to XRAYs and all the regulations. Would I need to do anything to get the chassis out of this "state" other than replacing components like I'm doing?

qrz

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Re: Mismatching tube issue
« Reply #3 on: October 06, 2015, 07:02:38 am »
was referring to the monitor's onboard power supply.

sry, i tend to forget not everyone speaks tech

Vilepickle

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Re: Mismatching tube issue
« Reply #4 on: October 06, 2015, 10:27:32 am »
No problem, I speak some but I'm still learning monitor stuff :)  Obviously, since I was dumb and blew this chassis with a wrong tube.

By power supply do you mean everything in circuit leading before high voltage? That's what I've been assuming so far and targeting my replacements at.

Vilepickle

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Re: Mismatching tube issue
« Reply #5 on: October 08, 2015, 02:47:16 pm »
I fixed this, I ended up blowing the HOT again since I didn't have D18 or IC4 replaced at the same time.  Woops :)