WG 4901 missing Red ... transistor question

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I searched past posts and gathered all the info I could. While I try troubleshooting with some of that info, could someone answer the following question?

What should the voltage measure at the collector, base and emitter of Q401 (red output transistor)? Thanks so much in advance!

Roger
 
I searched past posts and gathered all the info I could. While I try troubleshooting with some of that info, could someone answer the following question?

What should the voltage measure at the collector, base and emitter of Q401 (red output transistor)? Thanks so much in advance!

Roger

If you want to test if it's good, just swap with Blue or Green and see if the problem moves.
 
If I understand correctly, the three color output circuits are identical, so I figured I could just compare the voltage measurements before removing the transistors.
 
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You can also short the red gun to ground if the red gun on the tube is operational, you should see a red flash. You can also turn the red gun all the way up and see if the screen turns all red. I've had this before and if that's the case you need to replace the input transistor.
 
You can also short the red gun to ground if the red gun on the tube is operational, you should see a red flash. You can also turn the red gun all the way up and see if the screen turns all red. I've had this before and if that's the case you need to replace the input transistor.

How do I short the red gun to ground? To turn the red gun all the way up, do I use the drive pot or the cutoff pot? BTW, cutoff and output are the same, correct? Sorry, I'm still learning.
 
How do I short the red gun to ground? To turn the red gun all the way up, do I use the drive pot or the cutoff pot? BTW, cutoff and output are the same, correct? Sorry, I'm still learning.

I've never worked on 4900 we need Buffets input but what I'm saying is the concept.
 
If I understand correctly, the three color output circuits are identical, so I figured I could just compare the voltage measurements before removing the transistors.

The circuits are identical but the voltages going through them will vary. As Matt said you can also turn the red all the way up and everything should have a red tint to it.
 
You can also short the red gun to ground if the red gun on the tube is operational, you should see a red flash. You can also turn the red gun all the way up and see if the screen turns all red. I've had this before and if that's the case you need to replace the input transistor.

I just want to confirm that you did mean to say INput transistor and not the OUTput transistor. Thanks!
 
The circuits are identical but the voltages going through them will vary. As Matt said you can also turn the red all the way up and everything should have a red tint to it.

When I turn red all the way up, the graphics and entire background are a very faint red. Could this be the gun failing or would it be something elsewhere (like a transistor, etc)?

There is one thing I noticed and I would like to know if it could be part of the problem. On the game pcb, where the red, green and blue wires are attached at the molex connector, the blue and green voltage fluctuates between .1 to .4. The red voltage is consistently higher than blue and green, fluctuating between .2 to .7. Any thought on this?

I really appreciate the help! I'm getting a better understanding of all this and I feel like I am SO close to getting this fixed!
 
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I just want to confirm that you did mean to say INput transistor and not the OUTput transistor. Thanks!

I call the ones near the video input the input ones and the ones on the neckboard the output.
 
update

i tied the red circuit to the green gun and graphics are fine.
i tied the green circuit to the red gun and red gun is working.
but when i have the red circuit and red gun connected like normal, the red is very weak.

this doesn't seem to make any sense. something I'm missing?
 
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