Hopefully someone will chime in. I've had this happen to a couple of Dens I brought home. I ended up spraying the green leaves with Physan and while it obviously didn't help the already yellow leaves, it helped tremendously in keeping the green leaves green. It appeared to have stalled whatever it was from spreading. After doing some reading on the web, it appears it could be anything from a virus to root rot to being too dry to a myriad of things. If you've just repotted, presumably you've checked the roots.

Spraying with a physan solution may help but since we don't really know what's going on it's possible it won't. You could have it tested for viruses but someone else on the forum will know better than I how to accomplish this.

yes i've had physan and decided to give it a try, only two leaves survived so far on the tallest stalk.. so let's see. Would leaves grow back on the other stalks? or that's it they're dead, they seem green inside.

The leaves go yellow because the plant is in distress and the plant draws nutrients from them in an effort to survive.

Den. Burana Emerald is a warm growing hard-cane Dendrobium that needs warmth, bright light and moderate humidity to do well.

Think of the Climate in Florida, Hawaii, Tropical South East Asia for the conditions needed. Try to find some complete culture notes written for Northern USA.

It is normal for the very oldest canes to lose leaves. Still alive they support the actively growing parts of the orchids so do not cut them off.

Something shocked the plant, repotting or conditions???

This can happen with these hard cane dendrobiums being moved from a warm climate to a colder one. I have an Enobi Purple Splash that came green and healthy from a nursery in a warmer part of the country. Within a week the same thing happened. Yellowing of leaves and several falling off. I placed it on a heated tropical fish tank and within a month the leaves stopped yellowing and stayed green. A new growth also emerged.

So try to keep it in the warmest part of your house and well watered.

It's down to two leaves, one of them yellowing again. Its 90 degrees right now and it gets evening direct sun and also making sure I'm watering enough but not over watering.

If they all fall off will they grow back once it adjusts? or does it mean it died :( the roots look fine!

thank you everyone

No, leaves will not grow back. But fear not, your plant will adjust. Dends like a very bright light, so South facing window is better. Watch for new growth from the bottom of the cane. By the way, try to figure out which cane is oldest, which cane is youngest, it may help. Join AOS and go to their webinar page, watch "Dendrobiums demystified" video.