WG K7000 repair help needed: Neck glow but no one home

TheBasement

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WG K7000 repair help needed: Neck glow but no one home

I have a medium resolution Wells Gardner K7000 that is giving me tons of headaches. The monitor went out with a nasty smell. After checking I see that the flyback is toast.

1. I order and replace the flyback. After turning the game back on it blows the fuse immediately.

2. Next I replace the HOT (SD1398) and B+ regulator (STR3123) and do a cap kit. Turn on the monitor. It comes on, the games works, I am very happy. Its on for about 15 minutes. I turn the game off, move it back into its spot in the arcade and turn it on. Nothing. However, there is neck glow and the fuse is not blown.

3. Thinking maybe I had a HOT or regulator on the verge of tilting bad, I replace the HOT and B+ regulator again with new parts. Still nothing. I do have neck glow and no blown fuse. Adjusting screen and focus on flyback or brightness pot gives nothing.

4. I check the 5 diodes and big 2.7 ohm resistor that Bob Roberts talks about in the power supply. They appear to test good but I haven't replaced them. I also checked to make sure the hot and B+ regulator were not shorting to the chassis.

5. B+ reading is 112V. Not quite 123V, but I don't think it should give a blank screen now, should it?

I am at a real loss on what to try next or look at. I don't have an oscilloscope to check waveforms or pulses. Since medium resolution monitors are hard to come by in these neck of the woods, I would like to get this one fixed. The picture looks real good when it worked. Can someone help out or point me in the right direction?
 
Check all your solder and traces as mentioned in the sticky. Find the pic in the sticky and go over those areas...
 
Check all your solder and traces as mentioned in the sticky. Find the pic in the sticky and go over those areas...

I appreciate it but I've been over the sticky, and have checked all solder traces in the pics and where I put in new components. I just don't see any problems there.
 
When you say "go over", do you mean you looked at them and they seem fine, you put a meter on them and they register okay, or you actually wiggled the part on the top side while watching the pads underneath and then jumpered/fixed anything that moved even if it had continuity? The last one is the way to do it.

If you fuse is not blown, then you could check R103 to make sure it's not out of tolerance...
 
When you say "go over", do you mean you looked at them and they seem fine, you put a meter on them and they register okay, or you actually wiggled the part on the top side while watching the pads underneath and then jumpered/fixed anything that moved even if it had continuity? The last one is the way to do it.

If you fuse is not blown, then you could check R103 to make sure it's not out of tolerance...

I wiggled the top of them, they didn't seem to move. I reflowed the solder in key places, checked traces and checked continuity to parts that the traces lead to. All checked good. I checked R103 and its 2.7 Ohms. Just to be sure I replaced it but I am still in the same place, neck glow, no blown fuse. Also, the monitor seems to do the normal crackle/static sound that most monitors get when powering up. Makes me think the tube is getting juice/power. Still just a blank screen though. Uggggh.

I'm almost at the point I'd be willing to have someone fix her up for a fair price knowing I put in a new flyback, hot, B+ regulator, cap kit and R103. Any takers for someone that doesn't have a 40+ repair queue? I'd love to fix it myself, I am just not sure what else to look for.
 
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dude that sucks! so close!! the fact its powering up is good man, youve crossed a major hurdle there...

as to where to go from here, i honestly dont know.
 
well, did you try any of the basic stuff like turning the Screen pot on the flyback up to see if you get raster? if you get raster, like a grey screen, then I would say it has something to do with your video header where the signal goes in, or the ribbon cable attaching the neckboard to the deflection board... at least I think you could get a raster with that.

I don't know about any of the ICs if one of those might've failed or something and that would cause no video to appear.

you reflowed the signal header right?
 
well, did you try any of the basic stuff like turning the Screen pot on the flyback up to see if you get raster? if you get raster, like a grey screen, then I would say it has something to do with your video header where the signal goes in, or the ribbon cable attaching the neckboard to the deflection board... at least I think you could get a raster with that.

I don't know about any of the ICs if one of those might've failed or something and that would cause no video to appear.

you reflowed the signal header right?

Yes, I have turned the screen and focus all the way up, as well as brightness pot. Nothing on screen. I have also reflowed the signal header twice now. It doesn't seemed to make sense that I get a B+ and heater glow, but not even some white showing on the screen. But maybe I don't understand when monitors start emitting through the guns. I thought I read somehow to tie the middle leg on the transistors on the neckboard to ground to get all of one color, or tie a leg at the video input to ground to do the same. Does that work or will it damage something?
 
You could remove one leg of D10 to see if it comes up. That would at least narrow it down if it does.

Otherwise, I charge $50 + parts (if needed) + shipping to repair these...
 
You could remove one leg of D10 to see if it comes up. That would at least narrow it down if it does.

Otherwise, I charge $50 + parts (if needed) + shipping to repair these...

I pulled a leg on D10 and still nothing on screen. Just the 112V B+ and neck glow. PM sent.
 
Hmm. Missed that it was med-res. Check that little board mounted above the flyback and make sure both wires are attached...
 
Hmm. Missed that it was med-res. Check that little board mounted above the flyback and make sure both wires are attached...

That board above to the left of the flyback does have the 2 wires attached to them. Is it possible that the components on that board could prevent a screen image? I'm only saying that because when the flyback went it may have arced to one of the wires attached. How would I test those components or which ones would go bad? I guess it's weird that initially I did get an image after replacing the flyback and hot, so those components couldn't have been toasted that bad initially.

I tested the B+ at the big white resistor hanging on the left as well as on pin 3 on the neckboard. Both were at 112V. I just wanted to mention the other side of that white resistor was 166V. I know that's not the B+, but I didn't know if that was normal or not.
 
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Additional. Further inspection of the chassis shows that D18 is completely missing, just to little legs sticking up where it looks to have been snipped. A search through the forums shows that a few other medium resolution monitor shad missing D18's also. I was just wondering if someone could chime in if that was normal.
 
From what I recall, that is normal.

When I'm working on K7000 chassis and have weird b+ issues - and I've replaced all the usual suspect parts, checked all the solder and traces, etc - I find that replacing the IC sometimes helps...
 
From what I recall, that is normal.

When I'm working on K7000 chassis and have weird b+ issues - and I've replaced all the usual suspect parts, checked all the solder and traces, etc - I find that replacing the IC sometimes helps...

Which IC, as I have already replaced IC4 twice? Last night I spent some time with a continuity tester going over cables to the neckboard, major traces the provide voltage and specific parts llike the flyback, hot and IC4 following traces going out of them. Unless I missed something, I couldn't find any breaks.

I also checked for shorts across C36 and C38 and they were not shorted. C36 is the original critical safety cap. Is there a way to try bypassing it if it is causing issues to test?
 
Which IC, as I have already replaced IC4 twice?

The IC I am referring to is IC2. You could check the voltages at each pin per the manual to see if it looks okay, but I sometimes find the voltages can be okay and it still messed up. You could check the horizontal oscillator on an oscope if you've got one.

I also checked for shorts across C36 and C38 and they were not shorted. C36 is the original critical safety cap. Is there a way to try bypassing it if it is causing issues to test?

No. C36 should be a 6100pf cap, but sometimes I find chassis (especially the med-res) that have 4300pf caps. Usually the ones with 4300pf caps will still work, but I've run into some (non-med-res) that had 4300pf but wouldn't work even though I could find no other issues. I replaced it with a 6100pf cap (after find info that the wrong value could cause shutdown) and the 6100pf cap made the monitor work properly...
 
Just out of curiousity, would a bad C36 or IC2 cause a blank screen, or would it at least have a flatline or white haze if the screen control was cranked up? Because right now the monitor shows absolutely nothing, although B+ and neck glow give me some signs of life.
 
A shorted c36 would blow the fuse. As I mentioned in the sticky, a c36 that is out of tolerance will cause a dead monitor. So will a bad IC2. But then, there are lots of things that can cause it...
 
A shorted c36 would blow the fuse. As I mentioned in the sticky, a c36 that is out of tolerance will cause a dead monitor. So will a bad IC2. But then, there are lots of things that can cause it...

So I've been reading through all the repair logs that I can on K7000's. In the sticky I noted the following:

*******************************
Solution - Replaced C36 with the proper 6100pF cap, and the monitor now works.

I'm not sure why the 4300pF cap works with the old flyback, but not with the new flyback. Perhaps the new reproductions have a slightly different tolerance window that requires a much more specific value on C36 than the original flybacks used. But this is worth checking if you have done everything else and still have a dead chassis....
*******************************

So I checked mine again and I had the original critical safety cap of 4300pF. On the underneath side of the chassis was a capacitor in parallel with the markings 102G H (1.6kv). I'm assuming this might mean 1000pF and in parallel would give a total of 5300 pF. Someone correct me if I am wrong. Either way, I supposed that's why it ran for 15 minutes with the new flyback and then for whatever reason decided it didn't like the tolerances anymore. I'm grabbing at straws, but I suppose my next step is to source a 6100pF (1.6kV) cap. Bob Roberts says he has a new source for these, but doesn't mention if its the 4300pF or 6100 pF. Has anyone ordered these from Bob Roberts?
 
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I have gotten the 6100 cap from BobRob before, so that's probably it. It's a different type, so follow the instructions on installing.

As to the caps on the bottom. Those are usually there even for the 6100pf's, so I'd leave them there...
 
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