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Author Topic: Put plug backwards Yolk caught fire is it salvageble  (Read 521 times)

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sollima

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Put plug backwards Yolk caught fire is it salvageble
« on: October 12, 2019, 01:53:31 pm »
I did something stupid today. When I tried to measure the voltage of my CRT heaters one of the things I did was disconnecting the plug with vertical and horizontal signaal.

When I put it back it was a bit more difficult than I remembered but I shrugged it off to the age of the metals in the plug and pins. When I looked more closely to the plug after the incident I saw little pieces of plastic broken off.

But anyway I placed the plug in backwards. When I turned om my cabinet and waited for the picture I saw a bright yellowish light comming out of the cabinet. I immediately turned the cabinet off and blew out the fire. It was burning on the yolk.

Up on closer inspection I saw that the two resistor on the yolk were gone and one had been burning.

- Can this tube be repaired by placing new resistors? Or is the damage too great?
- If so, does somebody know what the values of the resistors are?
-If not, the chassis is a MTC9000, what TV can be a donor with the right yolk values?

I know, what I did was pretty stupid.

Here are some pictures of after the burn:





When I turned the plug back the right way the picture was not good anymore:



This is a picture before the burn (made before reattaching the wires):







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princess prin prin

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #1 on: October 12, 2019, 03:05:10 pm »
The resistors are 470 ohm. The yoke is probably good. Remove the resistors and replace them. The vertical yoke should measure around 14-15 ohm with or without resistors.

sollima

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #2 on: October 12, 2019, 03:14:14 pm »
Thank you, that is great news. I will disassemble the tube from the cabinet, clean and replace the resistors with new ones. Hope it will be fine.

Do the resistors have to be metal-oxide, carbon or any is good?


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princess prin prin

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #3 on: October 12, 2019, 03:16:14 pm »
They're carbon.

sollima

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #4 on: October 12, 2019, 03:17:48 pm »
Thank you.
I have one more question is the vertical pin 1 - 4 (start from the left)?


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princess prin prin

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #5 on: October 12, 2019, 10:49:15 pm »
Looking at the first picture, 1-4 (brown-red) is vertical, 5-6 (orange-yellow) horizontal. The resistors are soldered across 1-3 and 3-4.

sollima

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Put plug backwards Yolk caught fire is it salvageble
« Reply #6 on: October 14, 2019, 09:59:36 am »
Thank you for the instructions. I have replaced the resistors. Sadly It read 17Ohms after replacement. Donít know if that is a problem, but I have full vertical control. I can make the picture longer and shorter.

My problem now is that I have almost no width control. With the potmeter on maximum small it the picture is still way off screen. Itís like when I turn the horizontal pot half way nothing happens, but then it only becomes wider instead of smaller.

Could I have blown a capacitor on the chassis? Or are there transistors I should check?

Old:


New:


17Ohms:


Too wide: (see health bar)




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princess prin prin

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #7 on: October 14, 2019, 01:09:37 pm »
Check D12, D13, C36, C37, C40, C41, C42.

sollima

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #8 on: October 15, 2019, 01:39:22 pm »
D12 and D13 gave a two way reading. I replaced D13 from a donorboard. I have to go and buy the D12.
The capacitors were good. Although C36 was about 5.1 nF instead of 4n7.

I have a question about C36. When I got the chassis there was a 4n7 capacitor placed. But in the different manuals there is a different number 3n3 and 3n9. What should I do? Is 4n7 too far from those values that it is damaging other components (like the diodes for instance)? Or should it be OK and there is a third manual which states the 4k7 capacitor?

ĎOriginal capacitorí:


But in the manuals it states different values for C36:






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princess prin prin

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #9 on: October 15, 2019, 02:53:30 pm »
There were a few revisions of the MTC9000 chassis. When the main board is "MZ" C36 is 4.7nF (this is your case). The later "BZ" has 3.9nF for the 14-20" and 4.7nF for the 25-28". Replace with same values.

sollima

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #10 on: October 15, 2019, 03:31:45 pm »
Great thank you .

Do you perhaps know where I could find the schematics for the mtc9000 MZ 07 version?

Because this whole thing started with me wanting to check the voltage on R216 which as you can see in the 2 schematics is labeled 1 Ohm and 0,33 Ohm. Because I have a very, very small (only a band of 3 to 4 mm at the base near the connector) and very faint neckglow. I think that the resistor I placed of 1 Ohm is too high (I got the value from one of the schematics). I do get picture but I find it always dimm. Even though the brightness pot and R90 were replaced and the pot is wide open.

I would like to know/check what the correct value is for R216 for an MZ 07 chassis.



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sollima

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Put plug backwards Yolk caught fire is it salvageble
« Reply #12 on: October 16, 2019, 04:21:31 pm »
Thanks alot

I replaced the diodes and almost ready for testing.
« Last Edit: October 17, 2019, 05:41:10 pm by sollima »

sollima

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #13 on: October 17, 2019, 08:37:54 am »
sadly the problem was not resolved.

I will try tr16, tr17, c57 and c58 next.


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grantspain

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #14 on: October 17, 2019, 10:49:48 am »
4.7uf 50v bipolar cap normally causes that at c42
most people look at a cap and think thats ok without actually reading it

sollima

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #15 on: October 17, 2019, 05:33:41 pm »
Thank you for your reply. From what I read the first time I had the problem, I understood that C42 was the place to be. So I desoldered the capacitor and it measured 4.7uF.

I had replaced the original bi-polar cap in the past with an axial (see picture) like Princess Prin Prin suggested. (When I had trouble with the width too). But when it read fine, I thought to look elsewhere. And it worked fine until my screw-up.

Also the yoke Horizontal measured ok. I believed 3.9 Ohm or something, so I believe it must be something on the chassis as a result of switching the H and V around.

Do you suggest to look elsewhere?

The C42 I used:


How I attached it (not my chassis):

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #16 on: October 19, 2019, 05:52:00 am »
have you checked b+ is 130vdc , TR16, TR17, D12, D13

sollima

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Put plug backwards Yolk caught fire is it salvageble
« Reply #17 on: Today at 02:15:52 pm »
Wohoo, I am very happy to report that the width problem is solved. I have full width control back. From a burning yoke to a full working chassis and tube.

It was TR17. (I replaced the diodes earlier in this thread and my B+ was 133V)

Princess prin prin and Grantspain thank you very much for your time and help! Youíre great


Everything is back in view:

« Last Edit: Today at 02:18:37 pm by sollima »

grantspain

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Re: Put plug backwards Yolk caught fire is it salvageble
« Reply #18 on: Today at 05:38:24 pm »
you have done well to rescue this  :applaud: