XM-1801N Smoke coming from behind the yoke.

[brandonharrison1]

My Red Tent has a XM-1801N, in it and it had a blown fuse when I got it. Replaced the fuse fired it up and got a picture, albeit a bad one. Flyback was ticking/buzzing a bit and after about 2 minutes of running, smoke starts to come from behind, between the yoke and the tube. Could a failing flyback cause the smoke? I should mention that the picture remains on the screen even while smoking. It does appear also to have width issues.

 

[TheYeti]

I can't say if a yoke can smoke or not...

But I can confirm that the yokes are known for going bad on these monitors. It's a bit of a mystery as to why,..but a theory has been the drinks people set on top of the game that spills and leaks down and damages the yoke.

I'd remove the yoke and look for burn marks.

Ultimately, it sounds like this monitor will need to be rebuilt regardless.

 

[brandonharrison1]

Does this count as burnt? What do I need to do next? This was my first yoke removal. Not as scary as I thought...

 

[TheYeti]

Yea, I'd say that yoke is burned up. Bummer. It probably had a short somewhere.

You could test it's ohm readings with a multimeter. But I suspect it's shot.

Do you have the working yoke from the other red tent monitor you could use just to test with?

 

[brandonharrison1]

Yeah, I do have a yoke from the other monitor. As a matter of fact that monitor is a thing of beauty with an amazing picture. Do I dare remove the yoke to test, or call this a good bet and track down a new yoke?

 

[TheYeti]

Since your other monitor looks so good, I'd probably leave it alone.

If you are so inclined to ohm out that yoke to confirm it's bad, here are the specifications courtesy of Ken Layton:

SHARP XM-1801
CRT: Sharp # 470NVB22, 8 pin, 22.5 mm diameter neck
B&K Rejuvenator adapter: CR-31
Horizontal yoke winding: red & blue, 2 ohms
Vertical yoke winding: green & yellow, 15 ohms
Yoke part number: H1394CE
Flyback part number: F1408CE (4111A)


Also, I can give you a big tip:

I have done a confirmed yoke swap on this monitor. I can confirm that a skinny neck K7000 yoke will work on this tube. You just have to get the yoke wires matched up right so the image is not flipped or upside down. (Don't mess this up or you could fry the yoke)

If you happen to find a skinny neck k7000 yoke, let me know. I could use one too.

 

[brandonharrison1]

I'll be keeping an eye out for a new yoke then. Thanks for the help! What do you think about the buzzing sound from the flyback? Time for a replacement or wait until I try a new yoke?

 

[TheYeti]

A buzzing sound from a flyback is not normal. I believe it's usually caused when the ferrite core is vibrating. Some have overcome this by jamming toothpicks down the opening of the flyback! LOL

But if it were me, I'd have a new flyback waiting and ready but not installed yet. I'd get the new yoke installed first and confirm it's working. Then replace the flyback. I normally don't like changing more than one thing at once so that I can avoid introducing more issues.

Change one thing at a time and it's easier to track what works and what doesn't.

 

[brandonharrison1]

Thanks for all the help, again. I did just ohm out the yoke and I'm getting 2.5ohms and 15 ohms for my readings. Is it possible that something just got in there and cooked?

 

[TheYeti]

Oh and I should also mention that if you do end up using a K7000 skinny yoke...you might have to back the yoke away from the tube wedges. When I had it resting against the wedges, the colors were distorted on the edges of the screen. When I backed it off the wedges about a half inch, the picture was perfect.

 

[TheYeti]

Thanks for all the help, again. I did just ohm out the yoke and I'm getting 2.5ohms and 15 ohms for my readings. Is it possible that something just got in there and cooked?

Hmm, that is interesting. I believe your readings are ok and within tolerance.

Perhaps something did fall in there and got melted? I wonder if someone else has seen anything like that.

I suppose you could try cleaning it off but you would need it it be 100% dry before using it again. Just be really gentle with it.

Interesting for sure.

 

[brandonharrison1]

IT appears that the windings have some kind of clear coating on them. I am assuming that if this is the case that if the coating were to become damaged during cleaning that would be an issue. I want to make sure I know what I'm doing before I proceed.

 

[Eternaliquid]

Hey Yeti, Brandonharrison1 is my brother and we are working on my redtent. I've got a skinny neck, k7000 yoke, arriving tomorrow or Monday. First time yokers here. Any pro tips or words of wisdom?

 

[TheYeti]

Hey Yeti, Brandonharrison1 is my brother and we are working on my redtent. I've got a skinny neck, k7000 yoke, arriving tomorrow or Monday. First time yokers here. Any pro tips or words of wisdom?

Sure thing! I'm actually working on some red tent monitors this weekend.

I'm not in front of my computer right now but I'll reply with some info tomorrow morning.

Specifically about the color combination of the yoke wires.

 

[Eternaliquid]

Sweet! Thanks.

 

[TheYeti]

Putting the k7000 yoke on the red tent monitor was pretty straight forward. There a just a few things to keep in mind:

1. Obviously discharge the monitor. And be very careful sliding the yokes on and off. Also be careful not to be rough with the convergence rings. Those are old and brittle. Don't mess with them. Just take a picture where they were on the neck so that you can put them back in that same spot.

2. When you put the new k7000 yoke on, position it such that the yoke wires are coming out of the top of the monitor. If I recall, this is opposite of the original yoke you pulled off.

3. Slide the yoke down the neck as far forward as you can until it evenly rests on all the rubber wedges. (*Note you might have to pull the yoke away from the wedges later)

4. This step is important: The yoke molex on the k7000 yoke is not compatible with the red tent chassis. So you are going to need to clip that off and use the molex connector from the original yoke and splice the wires together. MAKE SURE YOU GIVE YOURSELF ENOUGH WIRE TO WORK WITH!

So here is how you wire it:

Yellow wire from k7000 yoke > connects to yellow wire on original yolk's molex
Blue wire from k7000 yoke > connects to red wire on original yolk's molex
Green wire from k7000 yoke > connects to green wire on original yolk's molex
Red wire from k7000 yoke > connects to blue wire on the original yolk's molex

Don't forget to put the convergnce rings back on, then tighten the yolk's set screw. Don't over-tighten it! You might need to adjust the yolk later anyway.

Keep in mind that when you first fire up the monitor, adjustments will have to be made. You might have to back the yoke away from the tube wedges. When I had it resting against the wedges, the colors were distorted on the edges of the screen. (The monitor looked like it needed to be degaussed) When I backed the yolk off the wedges about a half inch, the picture was perfect.

Might want to also verify your B+ is still 110VDC after doing all this as well.

GOOD LUCK. Go slow and be methodical!

SIDE NOTE: When I did this yoke swap, it totally worked for me. Monitor looks perfect on my upright popeye. However, (and this is really baffling me right now) I can't get the monitor to work in my red tent. I'm starting another thread on this.

 

[SCUBA King]

Putting the k7000 yoke on the red tent monitor was pretty straight forward. There a just a few things to keep in mind:

1. Obviously discharge the monitor. And be very careful sliding the yokes on and off. Also be careful not to be rough with the convergence rings. Those are old and brittle. Don't mess with them. Just take a picture where they were on the neck so that you can put them back in that same spot.

2. When you put the new k7000 yoke on, position it such that the yoke wires are coming out of the top of the monitor. If I recall, this is opposite of the original yoke you pulled off.

3. Slide the yoke down the neck as far forward as you can until it evenly rests on all the rubber wedges. (*Note you might have to pull the yoke away from the wedges later)

4. This step is important: The yoke molex on the k7000 yoke is not compatible with the red tent chassis. So you are going to need to clip that off and use the molex connector from the original yoke and splice the wires together. MAKE SURE YOU GIVE YOURSELF ENOUGH WIRE TO WORK WITH!

So here is how you wire it:

Yellow wire from k7000 yoke > connects to yellow wire on original yolk's molex
Blue wire from k7000 yoke > connects to red wire on original yolk's molex
Green wire from k7000 yoke > connects to green wire on original yolk's molex
Red wire from k7000 yoke > connects to blue wire on the original yolk's molex

Don't forget to put the convergnce rings back on, then tighten the yolk's set screw. Don't over-tighten it! You might need to adjust the yolk later anyway.

@TheYeti thanks for the help. I just did a swap to K7000 on a Sharp 1801 using your info above. Made harness connections, dropped it on and pic is perfect again on an almost burn free Sharp. Just need to converge and lock it down.

 

[87 t-66]

How is the convergence/geometry with the k7000 yoke?

 

[SCUBA King]

How is the convergence/geometry with the k7000 yoke?

Just for testing I slapped the yoke and neck board back on, no convergence rings and I would say geometry is about 9/10 and colors are 8/10.
I'll report back once I converge and lock down but I feel like it will be solid.
I already dialed it back down from oversize so I know it will also be able to fill the screen.

 

[SCUBA King]

Had time tonight so I socketed all three LM3900s, LM324 and both LS14s. Will play musical chairs with the 3900s while new are in transit to see if problem moves with 3900.

Will report back.