25'' K7000 no red

sparky5693

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I'm a newbie here so be easy...

I'm working on a wells 7191 25'' monitor from a mortal kombat machine that has no red. I tried grounding the red transistor, and I surely do get plenty of red, but that's the only time I see it. From what I understand, that would mean the tube itself is ok. Can someone give me some pointers on where to start?

A previous thread mentioned replacing Q4...
 
I *think* I read the schematic right...

Switch Q201 and Q202. Is the red there, but the green is now gone? If so, replace (what is now) Q202.

Just to be sure, I'd make sure Q201 and Q202 are the same model number before swapping them, because I'm not 100% sure those are the transistors I'm thinking of.
 
Q201 Q202 Q203 are the transisters on the board that plugs into tube.

Q201 is red
Q202 is green
Q203 is blue.

They all the same type of transistor.
 
So did you swap them around? Every time I've had an out color, it was a blown color driving transistor. Of course, I haven't worked on a monitor older than 2001...

Regarding Q4... the schematic says it's a 2N3904. Q1-3 are also labeled the same. If they are in fact the same model, swapping Q4 and Q3 (which is on blue) can't hurt.
 
I'll have to wait until this evening to give it a go. I'll probably start with the transistors.
 
GAH! I'm goofing up people's names! Sorry about that alpha.

I forgot something though. Sparky, check for a signal at pin 1 of connector P1. If the game has a color purity test, put it on white, and check the pin with a multimeter; it should be very close to pins 2 and 3 in voltage. If red is substantially lower, or just plain 0, your monitor is probably fine, and you have a game board or wiring issue. (An oscilloscope would be even better, as you'd be able to see the signal on your scope screen.)

Once you've confirmed that red signal is actually reaching the monitor, I'd definitely start with swapping Q201 and Q202; if you still have green but not red, try swapping Q4 with Q3.
 
GAH! I'm goofing up people's names! Sorry about that alpha.

I forgot something though. Sparky, check for a signal at pin 1 of connector P1. If the game has a color purity test, put it on white, and check the pin with a multimeter; it should be very close to pins 2 and 3 in voltage. If red is substantially lower, or just plain 0, your monitor is probably fine, and you have a game board or wiring issue. (An oscilloscope would be even better, as you'd be able to see the signal on your scope screen.)

Once you've confirmed that red signal is actually reaching the monitor, I'd definitely start with swapping Q201 and Q202; if you still have green but not red, try swapping Q4 with Q3.

If I have a color purity test, I don't know how to get to it, but I did check the voltage across the pins while the game is in demo. To me, the ranges I see across all three pins seem very comparable.
 
I think i'm leaning toward sending the chasis out for repair. I'm capable of swapping some components out, but I think i'd feel better if someone just gave the whole thing a look over. If anyone has a recommendation, drop me a line.
 
The problem with this chassis was a break in the trace from the red input pin to the next part in the red circuit. It was so small, I found it first with continuity testing, then with a magnifying glass...
 
BTW - this was a K7000A, not a K7000. Same troubleshooting methods, but some of the parts are ID'd differently...
 
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