7400 neck board issue help...

CalifTom

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Hello,

I have a WG7400 that has a failure in the neck board. When the board was replaced with a working one, the monitor came up (told to me by the person I am fixing the monitor for). In the photo there is a capacitor missing from C519 (upper left). Could this have caused the problem? If not, what should I try next? Thanks.
 

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I'd have to go dig out a 7400 to check on the cap.....can you tell by looking at the solder side if there was one there before?
It's hard to tell from the pic but double check EVERY solder joint on the neckboard especially ones belonging to large resistors and transistors which get hot. (probably missing heater voltage)
 
Yes, I can see the two stubs that should have been the legs of the Capacitor. I would like to know a bit more about the Heater Voltage. Should I take out all the transistors and test? Thanks.
 
Nah, the transistors on there would have nothing to do with the heater voltage.
I'll see if I can dig a chassis out to look at and I can point at stuff with it easier.

Is there any neck glow at all on the tube when this one is installed?
If yes - then you have heater voltage.
If no - you won't have any image at all.

C519 is listed on the schematic as optional, so I'll look to see how many of the 7400 series chassis I have actually have it there. It ties into the Contrast on that U500 IC, shouldn't kill your image.

Can you get a clearer picture of the solder side of that neck board ?
Hard to see some of the suspect solder joints.
 
Here are some new pictures. From the pictures you can see at least 3 other components that have been cut out. Are any of these components necessary?

R511, R512 and C521.

Thanks.
 

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I just pulled a few neckboards from my pile......all thre are done like yours with R511 cut out and Q501 jumpered, etc. C519 has been cut off two of them, the other doesn't look like it was ever there.

One of mine has a cap between the W515 jumper and the jumper in the Q501 spot. The other two I'm looking at looks they they used to have one there too. (I only pulled out three neckboard to look at, but can find more I'm sure) It's a 4.7uf 50v cap on the one neckboard.

Do you have a chassis to hook that one to in order to measure the heater voltage ?
 
Is there even any neck glow with this neckboard ?

Checking heater voltage -
Get it all set up on your chassis like it normally is on a tube and all that....... and measure the AC voltage on the two points on the neck I circled and also on the two points I circled where the ribbon cable connects.
Let us know what you get.
 

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When I fire everything up this is the image that I get. When I adjust the colors, the color does not affect the image. It just becomes a solid color. I can get Red, Blue and Green. If I turn the colors all up you can't see the image any more. Again, I was told that another neck board was put on and the image was clear. Any thoughts?

Here is the best image I could get.
 

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I pulled the blue driver transistor from the neck board and lost the picture and the blue. Here are a few pictures with the transistor missing and different colors being adjusted.

What do you see?

Thanks for the help...
 

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I went through the hole range. I just wanted to show that their was color there. But I can not see any image after the blue driver transistor was pulled at any levels.

I took out every transistor and checked them. All measured good.
 
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