WG k7000 transistor ?

RPO_Z06

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I have a WG k7201 that I installed a cap kit in because it had some leaky caps causing weak colors and waves.

I also had a friend rejuvenate the tube and test it.

Now I have nice green and blue but red is still weak, its not bad when cold but nearly fades away when hot, I was thinking maybe I have a bad transistor but I don't know what to look for, I've swept all the forums for information regarding weak colors and most of them lead me to believe a transistor might be bad.

Where can I buy them if I do need them and what part number or size does it take ?

Any other ideas on what could cause it ?
 
The part is Q201 on the neckboard. The easiest way to check it would be to swap it with one of the other transistors, if the problem moves the transistor is to blame. However, I'd check the solder joints on the circuit. If it is fading over time a cold solder joint is likely warming up and causing a bad connection.

Here is a link to the schematic:

http://arcarc.xmission.com/PDF_Monitors/Wells%20Gardner%2019k7201.pdf
 
Now I have nice green and blue but red is still weak, its not bad when cold but nearly fades away when hot

Does adjusting the red drive pot or red bias pot on the neckboard do anything? What about turning up your brightness or contrast? Anything make it better?

I was thinking maybe I have a bad transistor but I don't know what to look for, I've swept all the forums for information regarding weak colors and most of them lead me to believe a transistor might be bad.

Where can I buy them if I do need them and what part number or size does it take ?

It's possible. Q201 on your neckboard is for the red signal. You can test it with a multimeter on diode test to see if it measures the same as Q202 (green) and Q203 (blue). Also, check to make sure the solder on it's legs is good.

As for replacing it, it is a 2SC3782D transistor, which cross references to a NTE 2507 and can be bought at several different online parts distributors, such as Mouser:

http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMutXGli8Ay4kDd5Wfyyb50s9HW2XRTTBKo=

Any other ideas on what could cause it ?

1) Your red gun on your tube may be weak. You would need to have the tube hooked up to a tube rejuvenator to find out - and rejuvenated with it if that is the case. Some TV repair shops can do this for you, or you could ask if any of our members local to you has one.

2) Your red input pin could have cold solder, be dirty, or the wire may be barely making contact to the pin in the connector. Or your edge connector on your game PCB may be dirty or not making good contact. Your red control pots may be dirty inside. You could have cold solder joints at various points on the board, or even at the neck socket. Anything in that circuit that keeps the full voltage of the red signal from passing through the red circuit cleanly would cause weak red...
 
I'm guessing the red gun is the issue, I tried every test I could find on line and in manuals on it today and nothing seems out of order on the chassis or neck board.

I swapped in my backup K4600 and called it a day.
 
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