k7000 horizontal output transistor

warp655

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question , i tested center pin#Q11[horizontal output transistor] on my chassis board and came up with 0.69 ohms with the power off . I'm trying to trace down a blown chassis fuse . Would this be my problem ? Not quite sure how low the reading should be .How close to 0 ohms is a bad transistor? Thanks in advance
 
I personally use a continuity tester. If I get a beep when I touch the center leg and the frame of the chassis, it is a short. You might check the horizontal safety cap (big green 4 legged capacitor behind the HOT) to see if it is shorting out. Use the continuity tester and check for a short from one side to the other. You also need to check the rectifying diodes at the top of the chassis to the right of the fuse to see if any of these are bad. (You did use an isolation transformer to use this monitor right?)
 
thanks for the reply . it does have an isolation transformer installed and wired . I'll pick up a continuity tester and recheck . All of the wiring in the cab looks untouched . It must be a board problem .
 
If you have a meter with a diode test, then you would test the HOT with the black lead on the center leg and the red lead on both of the outer legs. You should get a reading between .400-.700 on both if it's good. Anything lower is bad. You will get a zero (short) reading if you try to measure between the outer two legs, but that is a false reading thru a low-value part. If you test it out of circuit in diode test, you will find that between the outer legs will measure about .087 on a good transistor, and between .400-.700 with the black on the center leg and the red on both of the outer legs.

I don't see a lot of blown fuses with bad HOTs though. Typically if the fuse blows, then you usually have a short in IC4, C38, C36, D18, or maybe even an arcing flyback.

Make sure that the ground wire from the tube to the neckboard is connected. If not, the chassis will spark to the frame and that will blow your fuse - as well as other parts....
 
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