Legacy goes haywire all of a sudden.

Just a shot in the dark......sounds to me the legacy base may be losing power after 2 hours thus causing the trains to go in conventional mode.  The 990 power supply may be overheating after 2 hours causing the base to lose power.   Try unplugging the power supply at the base and putting a meter on it while keeping the power supply plugged into the outlet...get a voltage reading.......then wait 2 hours, keeping power to the power supply then take another reading to see if any voltage drop.

I am sure others will chime in.

-Pete

do you have anything running through a power strip?

All my stuff runs through two power strips. Just ckecked the 990 power supply is by itself and the cab 1 base and tiu power supply is one the other power strip. Maybe this helps.

try removing the power strips.

they have been known to cause issues.

I believe the power strips cause range issues with the 990.

-Pete

Power strips will cause signal issue to the engines BUT it seems very unlikely this is the issue since you run fine for 2 hours. I suspect there is something in the base failing as it heats up. Once it cools down it works again. Try elevating the base off of what it's sitting on by putting something on the outside edges. This will help it stay cooler. This will at least possibly tell you if it's heat related. 

Typically the power strip issue is there or it's not. Unless something in the power strip is heating up and failing causing a signal issue. But I suspect the base. 

Any suggestion is worth a try though. 

Marty my initial thought was what you suggested.I will try that and see what happens. I had never run my layout that long with that much load before. Maybe my base is going bad. I have my new 990 base comming back from lionel this week. Very fast turn around time I might add. This is the second trip back. Hope they get it fixed. I belive they will. I sure hope this base is ok and not going bad or lionel will think I am doing something to these 990's. I treat all my stuff with great care. I even power up and down the layout in a certain maner. Btw tanks for the power strip info guys. Had never heard of that. My 990 base sits directly on a pine board with screws in the mounting hole to keep it in place. Maybe the air vent hole which is located on the bottom of the base is not getting enough ventilation. Maybe a big hole cut into the board directly under the 990 vent hole will be nessesary if marty's suggestion cures the problem. Kinda makes sense. Will run the layout tommorow and let you know what happens. Thanks guys.

Most often happens in power strips with surge suppression. It interferes with the earth ground side of the signal getting to the house earth ground.   Since Legacy and TMCC rely on the house ground wiring to radiate that half of the track signal some power strips can cause issues with it.  

There really is no additional load on the command base its just generating a signal. I suspect it's more to do with the length of time. 

FWIW, we had a 990 base on the club layout that would occasionally go off in la-la land and everything would stop.  However, they shouldn't take off like a rocket until they get a power cycle, then it's all bets off if there's no TMCC signal on the track.

What do  you guys plug in the 990 power supply to. The wall outlet directly or a heavy duty grounded orange type exstention cord. I was using the power strips on the bottom board of my control panel. This way I could easily shut everything on and off. The power strips are connected to a heavy duty orange grounded exstention cord with grounded three way spliter which allows the two power strips to be plugged into the one cord. I keep the exstention cord plugged into a good know grounded outlet. I only unplug the orange exstention cord from the wall if it storms really bad. Do not want lighting to damage anything. Is this set up ok or shoud I do something different?  Uploaded a photo of my control pannel. You can see below left the two power strips.

Thats exactly what I did without any problems......if you do send the base back for repairs....send the power supply too...

-Pete

Guys, tryed all the above suggestions. Put the base up on blocks. Also removed the 990 power supply from the power strip. Pluged it directly into the grounded exstention cord. Ran the same engines same smoke volume trying to recreate the operating scenario as before. Every thing ran fine. No hiccups this time. Even set the base back on the board as usual and every thing ran ok. If it occours while operating again I will let you know. Probably wont be running that long untill next weekend. Thanks for the advice.