Repairing a Mickey Mouse Lamp - UPDATED !

My daughter has a nice Mickey Mouse lamp.
We bought it years ago and it worked nicely for many years, until "somebody" connected it to an X10 Lamp module.
After few times, the lamp stopped to work completely.
In this article I'm documenting the repairing process.

The lamp

Here the lamp.  Mickey is pulling the cord every time the big red button is pressed, while some sentences are spoken, turning the lamp on and off.

The circuit

Inside the base of the lamp, are present four PCBs.

• Main control module
• lamp activation module
• pushbutton support
• main power support

The LAMP control module feeds the transformer via a main fuse, and it  receives from the Main control module the command to activate the bulb.
Here a picture of the inside :

On the left lower corner, it is located the main control module, just below the transformer.
On the right side, the LAMP control module.

Main control module

The main control module circuit, is the main PCB of the lamp.
The main controller module performs these functions :

• it power supply the circuits
• it controls the bulb  via the LAMP control module
• it controls a motor for some motion effects
• it generates sounds/voices when the lamp is activated/deactivated
• it handles the main on/off pushbutton

LAMP control module

The bulb  control module (called LAMP in the block schematic) feeds the transformer that power the main control module via a fuse, and it receives via photocoupler the comand to turn on/off the bulb.

Here a schematic of the LAMP module :
 

Open the lamp

It is quite easy to open the lamp.
On the base there are 4 adhesive pads. Under each pad there is a hole containing a screw that connect the base with the main body of the lamp.
After the screws are removed, the bottom of the base is coming out.
The PCBs and the transformer are screwed to the upper part of the base.
The only annoying thing is that all the wires are soldered to the PCBs, no connectors. 

The problem

The lamp was totally dead.
Measurement made on the LAMP  control module didn't show up any problem.

The diagnosis

Since all the functions of the lamp, motion, voice and lamp, were dead, as the first thing I checked out the  power supply.
Hooking a voltmeter to the transformer secondary (blue wires) showed up 0 volts.
Then I disconnected the transformer secondary from the main control boards and did again the tests.
Still 0 V.
So it seemed the transformer was gone.
To be sure of that, I disconnected also the primary of the transformer (cutting out the red wires) and removed it from the base.
The primary resistance of the transformer was infinite, the secondary one 0.6 Ohms.
So the primary of the transformer was broken, thus no power to the entire circuit.
I then hooked up a DC power supply to the main board control, when the secondary  of the transformer was connected.
Around 7V the circuit started to work.  Pushing the ON/OFF button the character spoke and moved as usual.
However connecting the main power (110V) to the lamp, the lamp remained OFF
Possible reasons :

• a) also the circuit that control the bulb had problems (SCR dead or some diodes broken)
  
  OR
  
• b) the LAMP control module needed to be driven with a signal in sync with the AC line
  Since I used a DC power supply to test the main control board, I didn't have any AC signal
  
  OR
  
• c) the bulb was broken

The last one was correct.
The bulb was broken.

The  repair

Since all the functionalities of the lamp were present when powered with the DC power supply, in order to repair the lamp, the transformer had to be substituted.
In order to do so, I had to figure out  what transformer to use.
The original transformer was labeled "HUNG KAI 4104".
A search  with google showed only a Chinese company who produce it (Hung Kai Electric Co) and that the model 4104  belonged in the category of transformers below 15W, with max. voltage of 42V.
Clearly the original transformer was  NOT sending out 42V, a main line capacitor on the main control board  was a 16V max electrolitic.
Since the main circuit board was working with 7V DC, my first guess was that the transformer had to be a 6V one.
I found on Jameco a 6.3 V transformer, 1.2 A , with dimensions "close" to the original one. 
Approx 6.3 V AC, once filtered  become around 8V DC

Here the "fix".
The transformer is little bit bigger than the original one, so it is attached upside down, with  some high heat hot glue on the top and a velcro support (not in the picture) on the base to avoid movements (safety must be always the first concern when repairing electric appliances).
It is also possible to see the rewiring (yellow and white wires) connected to the original wires (red and blue).
The small gray wire is the one in parallel to the original pushbutton, connected to a jack.
This is used to command the lamp with an X10 Universal module  (see below).
The unused wires on the transformer, were cut and insulated and glued to prevent short circuits.

The improvement

Since the lamp was open, I decided to add a jack to "bring out" the push button ON/OFF function.
In this way it is now possible to control the lamp with a remote push button or connect the lamp to a X10 Universal Module .

Broken .. again

Well, the lamp did broke again few years ago (now is 2020).
I did write the original article 10 years ago !!! WOW !!!!!

I did left the lamp in garage for some time, then I decided to at least see what the problem was.
I did re-open the lamp and I immediately noticed the fuse be dark .. clearly the fuse did blow up, maybe due to a defective lamp (at least I hope).
The fuse is a 125V 1A (ehm .. years ago I did speculate that the fuse was 15A in a message answer, wrong !!), with solder terminals (it can be easily spotted on the picture above) and OF COURSE on my junk box or around the lab I didn't have one.
So I did remove the broken fuse and ordered a new one, with a fuse holder.
I did order a 250V 1A fuse and is OK, it is OK to use a 250V fuse instead a 125V one, as long as the current is the same, not the opposite though !!
i.e. if a circuit requires a 250V fuse you CAN NOT substitute it with a 125V one !
Anyway, as I said, I did order the new fuse and soon will arrive.

.........

I did receive my fuse kit with some fuse holder and the 250V 1A fast fuse.
As predicted I was able to embed the fuse holder somewhere in the lamp base and fortunately not other components were damaged.
The lamp once again did come back to life :)

Click here to see an interesting article about fuses from my preferred magazine, Circuit Cellar Ink, the only magazine I still regularly read since 1989 !!!
Enjoy !