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Author Topic: 'Blue' short on CRT - Advice please  (Read 365 times)

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Nipedley

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'Blue' short on CRT - Advice please
« on: May 06, 2017, 09:15:16 am »
Hello!

My MTC9000 has been overwhelmingly blue since I first got it. I've finally decided it's time to get a good picture. Even when setting Blue Drive & Cutoff low, as you can see the blue bleeds into the white. I've attached a picture (MT1) of color bars test screen. Turning up the Blue Drive control does make it even more blue, so whatever is affecting this, it isn't a 100% short

With the blue transistor removed from the neckboard and no video input, this is the picture I'm getting (MT2). All controls are at their lowest here (RGB drive & cutoff), brightness is set to half, screen is set to the lowest setting that produces a picture - which as you can see is  blue

I've obtained a B&K 490 rejuvenator which I just hooked up. There were no leakage/short lamps lit, so I decided to do a very short 'Clean&Restore' function on the blue gun, probably around 2 - 3 seconds. I hooked everything back up and the picture is still just the same, still blue :-(

Without the blue transistor I fail to see how this could be a chassis issue? Should I do the 'Clean&Restore' function for longer? This is my first time using a rejuvenator. All 3 guns tested good as did tracking and life, and it does produce a lovely picture, it's just too blue !

Many thanks for any advice
« Last Edit: May 06, 2017, 09:17:03 am by Nipedley »

baritonomarchetto

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Re: 'Blue' short on CRT - Advice please
« Reply #1 on: May 06, 2017, 03:54:42 pm »
Switch the blue transistor with one of the other two, an look at the pic. If your blue is still too much, the transistor is ok. Start from there.

Nipedley

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Re: 'Blue' short on CRT - Advice please
« Reply #2 on: May 06, 2017, 05:02:09 pm »
Hi Baritonomarchetto

That 2nd pic (just blue) is actually with no blue transistor at all fitted to the board, so the transistor isn't a factor here. I'm pretty sure given that it's something with the tube?

ed12

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Re: 'Blue' short on CRT - Advice please
« Reply #3 on: May 06, 2017, 05:21:59 pm »
i do think u have the rejuv setup right ? i question that
the facts u state make no sense
here is a trick well in clean and blance do a "tap test" by this i mean tap the end of the picture tube NOT THE NUB ON THE END,BUT THE NECK
with the >rubber end of screw driver<  NOT USE THE STEEL END,and see if u get a flash in the picture tupe neck?
please be in clean and blance,and look for the flash on the blue gun only,DO NOT HIT TO HARD AS AS TO CRACK THE GLASS OF THE NECK,if this happens ? it means junk was on the chatrode of the tube
i will look at the setup colser

ed
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Nipedley

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Re: 'Blue' short on CRT - Advice please
« Reply #4 on: May 07, 2017, 03:10:59 am »
Yeah I'm pretty sure it's all set up right, I used the B&K 490 instructions and watched a youtube video of someone doing a Clean&Restore on all of his guns just to make sure I had it all right. It was difficult to find info on my tube however (Samsung 5130B22-TC) I did confirm the heater and G1 voltages were correct but I guess it's possible the guns are switched as well.

Thanks I'll give tapping a go. The G1-K short lamp isn't lit but then there's nothing to tell me the lamp isn't faulty either. Would it harm anything to try the button anyway? Beyond that doing a full 'Clean&Restore' cycle on that gun is the only thing I can think of to try. With Clean&Restore though, the manual says to hold the button until the meter reads 0.2 which is well into the red, but on the youtube video the guy said to not let it fall into the red which would put the meter around 1.0 (Orange) - which advice should I follow there?

Many thanks

Nipedley

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Re: 'Blue' short on CRT - Advice please
« Reply #5 on: May 07, 2017, 06:50:31 am »
Well, I think I have good news :-)

The tap test as you suggested didn't reveal anything, no sparks, however I decided to try the 'G1-K Remove Shorts' button and saw a spark in the neck. When I hooked the monitor back up, at low screen voltage there is still a very very slight blue tint (MT3) but if you compare to the low screen voltage pic above (MT2) it's much improved, and when I turn up the screen voltage I now get white rather than raging blue (MT4)

So I think when I refit the blue transistor I should be able to get that adjusted properly now. Also the guns all look good afterwards (MTguns). Great stuff! I wonder whether the G1-K Shorts lamp is faulty or whether the short was low enough that it couldn't pick it up. It seems to have done the trick anyway :-)

ed12

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Re: 'Blue' short on CRT - Advice please
« Reply #6 on: May 07, 2017, 11:45:22 am »
if the last picture of the b@k in emmisions? them guns are good

ed
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Nipedley

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Re: 'Blue' short on CRT - Advice please
« Reply #7 on: May 07, 2017, 01:13:04 pm »
Yep that was emissions :-)

I'm so glad the blue short is gone as it seems to be in really good condition otherwise, I would have hated to junk it

Blue transistor is going back in tomorrow so I can get to adjusting and then refit

Thanks for your advice everyone!

baritonomarchetto

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Re: 'Blue' short on CRT - Advice please
« Reply #8 on: May 08, 2017, 01:00:54 am »
Hi Baritonomarchetto

That 2nd pic (just blue) is actually with no blue transistor at all fitted to the board, so the transistor isn't a factor here. I'm pretty sure given that it's something with the tube?
Ops, missed that, sorry. Great job ;)

  
 

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