25" WG K7000 has Raster but no Picture

DaveHanes

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Hi all, I've been working on a 25" WG k7000 chassis, and have run into a problem I've not seen before. Here are the details:

1) The chassis had a bad flyback (was arcing), so I replaced the flyback, installed a cap kit, and put a new HOT in as well.
2) When I put the chassis back into the game, I get a raster but there is no picture (see photo below).
3) The game board is ok, I put a different k7000 chassis into the same cabinet and the picture was fine.
4) I replaced IC1 but there was no change. Was going to replace IC2, but the replacement hasn't arrived yet.

Any ideas on what to check next?

Thanks in advance!
 

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I've never seen it from my personal experiences with K7000s, but cadillacman (like our resident K7000 guru) says a common failure point on these is in the video header itself developing bad solder joints.

not entirely sure how it went from working before replacing other components to it not working now, but I'd reflow all the pins on the video header to at least rule that out.

are you sure you didn't install any caps backwards by chance? the K7000 has the + holes marked, unlike most chassis where they mark the -. lol
 
Thanks! I forgot to mention that I did remove the old solder and reflowed the video input pins.

I may not have been clear in my original message. The chassis didn't work originally. The flyback was arcing quite badly, so I didn't let it run for very long before I pulled it out of the monitor and started my repairs!


I've never seen it from my personal experiences with K7000s, but cadillacman (like our resident K7000 guru) says a common failure point on these is in the video header itself developing bad solder joints.

not entirely sure how it went from working before replacing other components to it not working now, but I'd reflow all the pins on the video header to at least rule that out.

are you sure you didn't install any caps backwards by chance? the K7000 has the + holes marked, unlike most chassis where they mark the -. lol
 
i aint no guru lol.. I was just unlucky enought o keep running into them.

next up after a quick solder check would be to shotgun the ics and see what happens. Thats definatetly not a common failure whatever it is and ill be adding this thread to the sticky for sure once you have figured it out.
 
Check the connections to the neckboard, and make sure that if yours had a cap to replace, that you put it in properly...
 
yeah mod dangit...

poster, look over the two 4-pin blue/white wire cables carefully. If one or a few are ripped, neckboard wont get a signal, and no pic... good call mod
 
Hi all, I'm back with an update and another question. I checked out the wires from the chassis to the neckboard (ohmed them all out), and all are ok, plus I reflowed those solder connections.

Now for my question, on the P5 connector (the blue & white wires closest to the flyback), my chassis only has 3 wires (2 blue and 1 white). The middle blue wire was cut off close to each connector, (both the connector on the chassis, and the one on the neckboard). Originally, I thought, well that's it, I just need to replace that wire. I took the connector off and was getting ready to put a wire in there, and then noticed that on 2 of my other k7000 chassis they also had that wire cut. But I have other chassis where it has all 3 blue wires + 1 white wire.

I was wondering why some chassis only have 3 and some have 4 wires?

Thanks!
 

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The wire that is missing is the ground wire to the neckboard. Normally it is there, but it is duplicated by a ground wire at P6 pin 1, so if you have ground there, then you don't really need the ground on P5 except as a backup. If you want, verify that you have ground continuity from the neckboard ground trace to the main chassis ground trace. If there is no continuity, well then you know why you have no pic...
 
Thanks, I had missed that earlier thread, so I'll check that out. It's interesting as my chassis also has that optional pincushion board, may just be a coincidence, but who knows.

Just to try and isolate the problem a little more I did swap in a different neckboard but the problem did not change...
 
Measure the voltages at the P5 and P6 connectors. The blue wires on the P5 should be about 6vdc, indicating the colors are going to the neckboard. if they aren't there, you may need to replace your color processing chip...
 
Hi, I'm back with more updates/questions! After looking at the thread that Cyberwhiz pointed me to, I found that I have no +12 on the neckboard (initially measured at P202 pin 1 on the neckboard). The +130 on P202 pin 3 is ok.

So, if I'm understanding this correctly, the +12 is generated from the flyback? I lifted 1 leg of resistor R92 on the chassis, and measured the voltage on the opposite leg (which comes from pin 5 of the flyback), and there is nothing there. This is a brand new flyback, so do you think it was just bad out of the box? Or could it have been ok, and something else caused it to fail?

I have another flyback, but didn't want to put it in until I consulted the folks on the forum!

Thanks.
 
This is the second thread I've come across that seems to be pointing at bad new flybacks.

That sucks....

If your missing +12 on the neck board your not going to get any sort of color drive thats for sure.
 
Hi, I'm back with more updates/questions! After looking at the thread that Cyberwhiz pointed me to, I found that I have no +12 on the neckboard (initially measured at P202 pin 1 on the neckboard). The +130 on P202 pin 3 is ok.

So, if I'm understanding this correctly, the +12 is generated from the flyback? I lifted 1 leg of resistor R92 on the chassis, and measured the voltage on the opposite leg (which comes from pin 5 of the flyback), and there is nothing there. This is a brand new flyback, so do you think it was just bad out of the box? Or could it have been ok, and something else caused it to fail?

I have another flyback, but didn't want to put it in until I consulted the folks on the forum!

Thanks.

Well, that's not exactly how it works. The +12 does come out of the flyback, but only if two things are true:

1) The flyback is good.

2) The proper voltage inputs to the flyback are good.

So, have you checked the inputs to your flyback to make sure you have what it takes to generate the +12?

I recall working on a G07 with a similar issue - only showed red, no green or blue - and it turned out one of the parallel resistors on the input to the flyback had gone open, causing the voltage to change enough that it wouldn't show me those colors.

If you have another flyback, and want to check, it's not that hard to swap them out....
 
I have a similar problem as the OP. My monitor is a 25K7191 with a P538. Raster lines, but no picture. I'm using the K7000 manual which references the P447, but I figured it would be an OK base reference for my monitor. Here are some of the voltage readings I have taken so far:

P5 - Pin 1 12V, Pin 3 130V, Pin 5 3.6VAC (which is lower than what I have read it should be around 5-6VAC, no clue if this is OK or not)

P6 - Pins 3, 4, and 5 all at 1.28V (I've read from Mod it's supposed to be around 6V, so I trace back)

IC1 - Pins 17, 19, and 21 all at 1.3V (typical voltage according to manual for these pins is 1.7, but that is for a P447, so not sure if this is acceptable)

IC1 - Pins 2, 4, and 6 start at ~2.5V but drop gradually down to .2V and lower while my meter is on them.

I checked voltages at transistors Q1, Q2, and Q3 as well as at diodes D5, D6, and D7 and all those seem to be within specs (which leads me to believe the solder of the pins at P1 is OK)

I can't find specs for caps for C4, C5, or C6 in the manual, but get about 1.4V on one leg of each cap and .5V on the other (side closest to IC1).

The guy I got the monitor from said it had a cap kit done at one point, and to me, all three of those caps failing seems unlikely. I'm leaning in the direction of replacing IC1, but thought I would ask first. Does anyone have any other ideas? Is there something I'm missing/overlooking that I should test first?

Checked voltage at Q4 for the hell of it. Found 12V at the collector, and 0V at both the base and the emitter (manual says base should be .1V), I'm still lost.
 
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There is a cap under the flyback cage that is easy to put in backwards. When you do this R90 and/or R92 can burn up and go open. Check those 3 parts and change all 3 if the cap was backwards.
 
I checked a few components around that area. I have ~12V on both sides of R90. I'm not quite sure which cap you're talking about (C42 is a large black cap and C43 is a small orange cap), so I checked both. C42 is installed properly according to the + on the PCB, I don't know how to check polarity on the smaller orange cap (C43)(Edit: after some googling, I guess most ceramic disc caps don't have polarity). Anyway, I have 12V on what is marked as the positive side of C42 and the ground side has a good ground. The cathode side of D14 is at 12V, and so is the same side of C43. The anode side of D14 is -0.24V with my black lead on ground and red lead on the anode side (and what I think is the negative side of C43), and -0.06V coming out of R92. The back side of C43 looked like it had a cold solder joint (small crack), so I reflowed that joint and retested, same outcome. Does anyone know what the voltage coming out of C43 or going into Pin 5 of the flyback should be? I'm beginning to suspect a bad C43.
 
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