TPC froze up

Did you try setting to default.

Bill

As Bill says, that's always a good first step.

If that doesn't do it, here's how I find those issues.

For the SC-2, I use a fine nozzle on a heat gun and warm components individually until the failure occurs.  Then I use the cooling spray to isolate it. 

The TPC sounds like a component has simply failed.  Dale Manquen used to repair those, and I think he still does.  He can probably fix the SC-2 as well.

I have had two TPC 300's on my layout for a number of years without any issues. However, once in a while they seem to lose their programing for some unknown reason.

One thing to keep in mind about the China produced versions they are very susceptible to power spikes. I would recommend that the proper TVS be installed on both the inputs and outputs of the TPC's.

 After reading the suggestions above, I called Boxcar Bill, a fellow west Virginian, to

get the particulars on resetting the TPC to the default state.  Bill walked me through the reset, but it made no difference in the operation of the unit.  Bill instructed me to remove the hot, power out connection from the unit.  This should have killed the power to the track.  IT DIDN'T.  In fact a voltage reading showed 18volts on the disconnected power out wire. Bill and I agreed that a short somewhere in the layout wiring was feeding the track 2 bus without the TPC being involved.  Since I have 22 blocks on the layout, I started shutting down all the blocks powered by track 2 TPC.  I started at the first block, block (2), and proceeded in order. When I shut down block 7, the power, to track 2 went off.

Block 7 is a siding which has my culvert loader/unloader set and a crossover from

the siding to a main line o track 2.  The crossover turnout is so close to the accessory that a slight movement shorted the eighteen volt turnout constant voltage pin to the accessory frame.  The pin casing melted and the wire fell across the crossover track applying 18 volts to block 7. Replaced the pin and heavily insulated both the pin and the accessory frame. everything, including the TPC is working perfectly. Thanks to those who offered suggestions and especially to Boxcar Bill for all his help!!!