K7000 missing red

obitus1990

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K7000 - 19" P447/P456. Missing red. I know, plenty of these threads, flowchart, zenomorp videos, etc. -- I've read them all and have been working on this chassis all day long.

Recapped, reflowed the entire neckboard, reflowed all problematic areas on the main chassis, INCLUDING signal input header and the small header (P201) that connects the color wires from the chassis to the neck board and its source from P6 on the chassis. Checked continuity of aforementioned wire between neckboard pins on P201 and the P6 connector on the mainboard to make sure the wire wasn't broken - it isn't.

Tried different game boards, different harnesses and a test pattern generator -- all have no red.
Swapped color transistors on the neck board -- no change
Swapped color transistors on main board - no change
Pulled all of the transistors and tested them via diode test and all passed.

Pulled and tested the red drive and red cutoff pots, also verified the right ratings were in the right positions (2Kohm vs 200 ohm).
Checked continuity of neckboard socket to make sure the RED pin was connected (pin 7) in the socket to the solder tail on the back side of the board, and it's good.

Tested the chassis with another tube, it has the same problem, tested another known good chassis on this tube, it works fine -- problem follows the chassis.

Turning up the red drive to maximum (or was it the red cutoff, I cannot remember -- maybe both did? ) will make the screen turn completely red - so according to posts by mecha, this means the problem isn't with the neck board.

About the only thing I have not done is swap IC1, because I don't have one on hand. I also don't want to spend $12 plus shipping on this IC if it's not the problem. Is there anything else I'm not considering here? All the passives in this circuit look to be OK and test within spec, in circuit at least. Is there a way to test IC1's functionality without pulling it and replacing it?
 
Last edited:
fuckus here

K7000_25_27_inch.jpg

otherwise, suspect IC1, maybe, I guess. once again, never a problem I've had. you've determined that the color drive circuitry works, you're losing red in the signal input stage. it's an issue I've seen on K4900s and while I have fixed that problem, I don't really know how I've done it. lol
 
You can mostly Ohm out the Signal pathways on these monitors. I would be looking at that IC chip myself, They fail in Odd ways at times. Also you can Short across the Drive Transistors and force the gun to come on Full Just to make sure that part works.
 
You can mostly Ohm out the Signal pathways on these monitors. I would be looking at that IC chip myself, They fail in Odd ways at times. Also you can Short across the Drive Transistors and force the gun to come on Full Just to make sure that part works.

Please explain shorting the drive transistors to me, as in what are you shorting what to (collector to base? emitter to base? emitter to collector? one of the aforementioned legs to ground?). Also are you referring to the color transistors on the neck board or on the main board?
 
The color Transistors on the neckboard. and TBH its been FOREVER sense I have done it so IF I were you I would look up the pinout of the transistors and short the input to the output to see if the gun itself works. I "Think" it is the 2 outside pins but I am NOT sure off hand so you need to check the pinout.
 
Stupid question.. have you validated the connection from the chassis to the neckboard?

As you have more than one chassis, move the neck board to another chassis and see what it follows. I know you did the drive adjustments but this also tests the wiring and connectors.

A scope would make this really easy to walk through the circuit.
 
I went back over everything today before replacing any more parts, like IC1 and the color transistors on the main board and the neck. I had reflowed the signal input header when first starting to rebuild. But I did not check it for continuity. I began with that today, and from the red pin on the signal header to the very first point afterwards, there was no continuity. I missed the fact that the trace was actually cracked here, right at the eyelet where the red pin meets the main trace! Man, I can be so dumb sometimes...most times. Anyway, it works 100% now.
 
I went back over everything today before replacing any more parts, like IC1 and the color transistors on the main board and the neck. I had reflowed the signal input header when first starting to rebuild. But I did not check it for continuity. I began with that today, and from the red pin on the signal header to the very first point afterwards, there was no continuity. I missed the fact that the trace was actually cracked here, right at the eyelet where the red pin meets the main trace! Man, I can be so dumb sometimes...most times. Anyway, it works 100% now.
Lmao the main thing is you got it. I always try to remind myself to always think about the obvious first, but i still do it too… because im bullheaded or something or hungover thats a better excuse
 
I went back over everything today before replacing any more parts, like IC1 and the color transistors on the main board and the neck. I had reflowed the signal input header when first starting to rebuild. But I did not check it for continuity. I began with that today, and from the red pin on the signal header to the very first point afterwards, there was no continuity. I missed the fact that the trace was actually cracked here, right at the eyelet where the red pin meets the main trace! Man, I can be so dumb sometimes...most times. Anyway, it works 100% now.
notch 10 more kills, then I'll claim you as one of my inventions
 
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