WG K7000... Horizontal collapse... what jolly fun....

Rattanee

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WG K7000... Horizontal collapse... what jolly fun....

Okay so I have this WG K7000 that I have a history with at this point. This thing has gone out of it's way to stop me from making it work since the day I got it.

When I got it, it had jailbars but worked okay... so okay, time to recap this sucker... I did a recap, replaced a few trimpots that were flakey, and a ceramic cap or two that were chipped.
I noticed that there was a plastic piece under the pcb, thought it just fell in there sometime during it's life. Turned out the chasis was arcing to the frame and it was put there to stop that from happening... Replaced a diode (D18), then after even sealing the flyback up with silicone, it was still arcing here and there, even managed to fry my test pcb with it...

I put it aside to work on when I have the time...

Recently I found a new flyback locally rather cheap, so I pulled it out to fix. Replaced the flyback, and upon powerup, amidst a horrible screech the monitor went into shutdown. No ground cable to the tube attached... thought that was the issue, so I go and attach it and try again, screechin noise, flash, nothing... Fuse blew, HOT a total short across all three legs, D18 total short (it also turned out that my replacement for this diode was inadequate for the task...).

So today I got two new HOTs in the mail, and a diode that's fast enough to replace D18 (though rated at 12 Amps... but I'm hoping that should not be a problem). It is a BY459X/1500. It has basically the same ratings as the sanyo diode that's virtually unavailable in Europe (NTE replacement costs $31 to ship a SINGLE diode to Hungary... I bought the new flyback for that price...)
I installed them, put in a new fuse holder, new fuse, fire it up, and... yaaay... I've got high voltage, monitor sounds normal aside from a faint fluctuation of frequency on powerup (I might just be imagining this... not sure... if it's there, it's very faint)...
Out of safety I still didn't give it an input. After metering the input leads and everything I was going to touch for leaking voltage (found nothing luckily) I turned up the flyback to see the raster... and all I got was a vertical line... (So yes it is a Horizontal collapse, I'm not mixing it up with a vertical problem)

The new hot is an original Sanyo part.

I've been unable to dig up anything concerning this sort of failure on this chassis, so I'm open to all ideas you guys may have...

I'm wondering at this point, if it's possible that the diode I put in actually needs a certain load to function properly... It might not conduct without a given load? Would I get the same results if I omit D18?

Since I get HV, I'm assuming this is a problem somewhere after the HOT. I checked both the linearity and the horizontal width coil, they are both soldered in properly and are conducting properly aswell. I checked the traces for continuity in this section, all test okay. Diodes D18 and D15 test okay aswell.

-I don't have an ESR meter, but I pulled C38, it reads at .406uF.
-C36 is definitely not shorted, so even if it's not good ESR-wise, it should not cause a collapse I think.
-C69... -where- is C69 supposed to be located? I looked until my eyes fell out but could not for the life of me find it, and it wasn't on the board layout drawing either that I had (even though the parts list listed it).
-What kind of resistance should I get across the linearity and width coils? Near zero right ?

Any ideas where I go from here?

(Btw the yoke connector fits snugly, yoke coil meters 11 ohms or so measured at the plug so it should not be a connection issue...)
 
Addenda:

I seem to remember WG boards commonly having a disc shaped cap sodelered to the underside... I don't see that on this one... was that not on this model? Or would that be the C69 I'm so desperately looking for?

And another thing.... (yes I'm hating WG more and more with every day...) The PCB has P538 printed on it... yet it doesn't have a remote board, but all the controls are on the pcb directly... Another screwey thing is that C38 is still the old style four legged giant cap... can anyone help me sort this out? I'm not sure at this point which schematic to look at... it's a 25" monitor from a sega game.

Any help would be ever so appreciated.
 
This is a strange problem. I've never seen a WG 7000 series minitor with horizontal collapse. They usually go into shut-down (or immediately kill their HOT....thus, dead). Check the couple big poly caps in the high voltage section for shorts. Check diodes D15, D16, D17, D18 & D14.

Edward
 
I agree with you that it's probably after the HOT, although if you have an extra HOT you may want to swap that in. It may be the diode inside the HOT is giving you problems.

The horizontal circuit is pretty simple, you have

C38 (works in tandem with the HOT to feed the yoke, the voltage leaking out of the cap makes the yoke throw the image to the right edge of the screen)
Q11 which is the HOT itself.
C36 (retrace capacitor, this probably isn't your problem)
Flyback (you may have a bad solder issue going on)
Yoke (if your yoke is dead open you won't get any deflection)
L2 Horizontal Linearity coil
L1 Horizontal Size coil (you checked already)

The best I can tell, everything else either deals with high voltage (which you have!) or Frequency/Sync controls (which I THINK is irrelevant to deflection, although the sync signal is what turns the hot on and off... I'll have to think about that one, though)

I would check your Yoke, it should give you less than 5ohms or so resistance, the horizontal size coil I know is pretty low too, 1ohm or so. Not sure about the linearity coil because I've never messed with it but yes I would imagine very low resistance (it's a coil!).
 
Things are getting weirder...

I double checked everything past the HOT, reinforced all solder joints. Replaced C38 with one from another monitor. Hooked it back up, and when turning it on, I got a rather nasty screech, and HW crackle. The back of the tube was actually sparking and -not- around the anode! (Note that the tube is clean so it's not arcing out due to dirt buildup near the anode) I saw something near the fuse light up orange for a moment, but the fuse is not blown and I see no burnmarks anywhere.

Maybe my HV is too high and the shutdown circuit is not working? (I didn't leave it on long enough to see if the collapse is gone...)
 
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Okay further analysis results:

Lowered the input voltage (Game I was testing it off apparently hasn't been set to 240v operation yet (we fairly recently had a change from 220 to 240 volts in the outlets) and was feeding the monitor 133V) and checked B+, B+ is a stable 127.7VDC.

I have Horizontal deflection now! Guesing it was C38 at fault as I didn't change anything else.

However! The monitor doesn't sound healthy... There's quite a bit of crackling when I start it up, and I'm still getting the flash of little sparks along the back of the tube when it starts up... the tube is rather clean as it has been mounted face up in it's original cab. What the heck could this be? Going to clean around the anode with precision contact cleaner just to be sure...

When it starts up, for a second it seems to have a nice high frequency sound then sounds like it's suddenly loaded a bit too heavily, lowering in pitch... (At about the same time the tube crackles) it seems stable after that... is this normal for the K7000? (Its's my first and only K7000)

There's probably some overfoldin vertically but I sorta expected that (Changed 50-60hz pot and as I read that bein misadjusted can cause overfolding)

---------------Further update-------------

Something is definitely not right... Pretty sure at this point that the HV is way too high. I just noticed someone has replaced the HV shutdown pot... so I've no idea if the shutdown circuit even works right but guessing it's not working at all.
Any ideas what could cause this?

Turning the Focus pot up blew the fuse. Hoping it didn't take the HOT with it.
 
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Id bet your yoke is the problem.

If your getting the High Frequency Squeal (15.6K) and HV, then the Horizontal oscillator is working, and the HOT is driving the circuit. Most likely, the yoke plug or the connections at the yoke itself are to blame. The sparking is likely the result of a bad connection occasionally acting like a good connection.
 
What are the correct yoke readings for a 25" K7000?
I'm getting 11.1 ohms and 1.9 ohms. Seems good to me.

The arcing happens on the glass surface of the back of the tube, not necessarily near the yoke. It looks just like when the anode is arcing around the suction cup, but this is around the back of the tube. I'm somewhat suspecting the tube could be at fault aswell thouh...

Would the tube off of an U5000 or U2000 work with this chassis?
 
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Okay I'm pretty annoyed at this point so I gave this a more thorough look. Could any of the gurus enlighten me about the caps in the HV section...?

I found two schematics, for the 20" and for the 25", with the p447 and p538 cassies respectively. The 20" marks C36 as the special two legged 6.1nf cap and has no C69, the other marks C36 as 3.6nf and C69 across D18 as 6.1nf.

My chassis has P538 printed on it, but has the four legged cap, but said cap is a 4.3nF cap (looks factory too, it's green and has CRIT SAFETY CMP printed on it, and measures 4.4nF),and I found no location for C69! What is going on here? Would C69 be the disc shaped cap I see on the bottom of pics of this chassis?

Thanks

---------------------
Experiment:
With the fuse the hot blew aswell, but seemingly nothing else. Replaced the hot, added a 6n8 cap (closest I could get) parallel to D18, powered it on, I only Got a brief crackle (no sparks that I could see), but the high voltage just sounds bogged down. The frequency is definitely lower then it should be... Anyone any ideas? I'd like to get this thing going if nothing just out of spite at this point...
 
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Not all K7000's have a C69.

Do you have a dag wire on the back of the tube connected to ground on the chassis - usually on the neckboard but sometimes on the left wall?
 
Yeah tube ground is connected to the heatsink next to the flyback. Neckboard is connected to the same place.
 
So this is giving me a headache but my will shall make this thing work! :D

Could someone give some intel about tube-swapping? How many ohms can the vertical coil vary? I have a tube from a U5000 and a U2000 handy. One of them is a .1 ohm difference in horizontal, but the vertical is somethign along the lines of 7 or 8 ohms instead of the 11 on the current tube... would I fry the chassis if I tried the other tube?

I also read in the common faults post that the 4n3 retrace cap won't always work with new flybacks... Seeing how my shutdown circuit is probably mal-adjusted, it'd make sense for it to try and come up with the 4n3 cap, so as a last resort, tomorrow I'll try putting in a 6n8 retrace cap (I know it's not the right value but the only one I can get my hands on atm, if it fixes things, I'll source an original 4 legged cap)
 
You will not likely fry the chassis. In fact, the K7000 chassis seems to be pretty universal when it comes to yokes.

Is the DAG coating still present on your current tube? It is a black conductive coating that should cover the bottom 1/3 to 2/3 of the back of the tube. This material acts as a conductor that the DAG wire is leaning against and in turn the DAG wire is grounded to the chassis. It sounds like there is a break in the conductivity between the DAG and ground and that is what is causing your arcing.
 
You will not likely fry the chassis. In fact, the K7000 chassis seems to be pretty universal when it comes to yokes.

Is the DAG coating still present on your current tube? It is a black conductive coating that should cover the bottom 1/3 to 2/3 of the back of the tube. This material acts as a conductor that the DAG wire is leaning against and in turn the DAG wire is grounded to the chassis. It sounds like there is a break in the conductivity between the DAG and ground and that is what is causing your arcing.

I guess I'll try the U5000 tube too if all else fails.

The DAG coating is the grey-ish-black stuff right? It's more or less present, seems scratched here and there... it actually looks as if the arcing that I saw ran along the edges of that coating. Why would that cause any trouble though? I thought what could cause such arcing in this chassis is if there's no ground wire between the neckboard and the chassis ?

The wire coming from the tube is connected to chassis ground, and I even tried adding in extra wires hooking together the ground point on the neckboard, the frame, and the chassis gnd all to one point. Still crackles.
 
The DAG coating must be grounded to the neckboard/chassis. If it is not you will get the arcing you are seeing and it will damage components eventually. Can you check for continuity from the wire running along the bottom of the tube to the neck board ground point? You should have virtually no resistance between those two points. Also, make sure the wire has good contact with the DAG. If it is floating it is not where it is supposed to be and will not do its job.

Finally check for continuity from the DAG itself to the neckboard. Often you will see a bit of resistance here due to the fact that the wire is dragging along the DAG and not hard wired to it.
 
I'll definitely check this aswell tomorrow. I suppose it -is- possible that the coating has worn away enough to stop conducting...
 
also yes the yoke you are using is one of the factory yokes that came with K7000 chassis/tubes.

it measures fine so i would not swap tubes or yokes.

Peace
Buffett
 
Thinking about it, what is weird is that When I had the vertical collapse, I had no arcing at all...
 
also yes the yoke you are using is one of the factory yokes that came with K7000 chassis/tubes.

it measures fine so i would not swap tubes or yokes.

Peace
Buffett

Thanks, I thought that the yoke was fine myself, but not so much about the tube... I don't intend a permanent swap, would just like to be sure it's indeed not something odd with the tube. I hope it's going to be just a grounding issue with the DAG coating, but we'll see tomorrow.
 
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