X10 - notes about the CM11A

WARNING !   X10 stuff is connected to the power grid !
If you don't know what you are doing, don't do it !!

YOU are responsible for your safety !

The CM11A 
 
The CM11A is a controller, one of the first controllers, used to create scenery and macro with X10.
Has a RS232 interface, to allow a PC to program the unit or use it as "interface" toward the X10 plant.
Was part of the CK11A kit, one of the first ActiveHome kits.

The problems

The CM11A always had some problems.
The most famous was (or is) the overheating.
There are tons of material about this problem, and also some solutions, like the one on the Ido Bartana website, devoted to X10.

Another intermittent problem, is related to some internal failures over the years.
Usually, every 5 or 6 year, a unit is expected to die.
Few years ago (was the 2002) one of my unit died, so I decided to repair it.
Now, few days ago, the unit I put to substitute the one broken years ago died as well.

So in this article I'm trying to collect the information to repair the CM11A.

The overheating
Sometime the CM11A suffer of a problem that become apparent with the total stop of any activity and a overheating of the unit itself.
Here an article that describe in detail what happens and a possible solution.


Unit receive, connect to the PC but not send any X10 signal
The problem, is related to a transistor that is connected to the transformer.
Since the unit is capable to receive X10 signals, we have to assume the transformer and passive components are alive.

Basically Q7 is the transistor that receive the X10 signal from the microcontroller and drive the transformer.
If this transistor is dead, no X10 transmission happens.
The transistor originally was a 2SD667 (Japanese transistor).
I replaced it with a normal high voltage NPN (I used a MPSA44 Motorola).
Open the box is extremely easy, is enough to unscrew the 4 screws at the bottom with a small Philips and gently separate the two plastic shells.

Here some pictures to help to identify the transistor in the circuit.

The transistor is close to the transformer metal enclosure, the one that became hot for the overheating problem.
I suspect that the cause of the death of such transistor is due to the overheating and the time.
The PCB close to the transistor is well cooked (not easy to see from the pictures, just believe me).

There is no need to detach the cables. Just gently extract the circuit bending the cables.

After the fix the unit restarted to work as usual.