Microwave oven front panel keypad repair and modification

Here is the video on youtube. You must watch it if you are a Urdu to Hindi viewer:

Here is the video on youtube. You must watch it if you are an English viewer:

The microwave oven is a useful machine to preheat or cook food. The microwave oven is working reliably but now a days Chinese microwave oven have big front panel keypad failure. The keypad is breaking down in one year of less time. The repair is not easy and sometimes the replacement parts are not readily available then it becomes another problem. The solution to such a problem is a modification with existing easily available parts and some wire connections to the main board. The modification is a very robust an reliable work so that will never break down or if breaks down, the repair would be way easy and low cost.

Here is a little detail with images is included for such a modification work. Most of the images are from the video associated with this blog post. Anyhow it will further explain the important points.

Here is the schematic diagram for the unit keypad:



Here is the front panel for the microwave oven.

First we will open all three or four screws with is holding the main PCB to the front panel.

No we will open the keypad connector for the keypad ribbon cable. So we will be able to remove the keypad ribbon cable from the main board blue connector.

Now we will peal off the front panel plastic sheet which is label also for the microwave oven. It is stick by glue. Sometimes you may need hot air to remove it from the front panel.

Then peal off the key pad from the front plastic label sheet. The keypad is made of two sheets of plastic. it contains circuit for keys.

Now mark all keys using a sharp object like a nail, needle or a knife to make the keys impressions and mark all keys centers on the front panel.

All the marks should be very much clearly visible and should be center punched for drilling.

Now select appropriate size drill bit. The drill bit should be the size of the micro switch used for keypad.

Do holes using drill machine on all marks for keys. The holes should be of enough size so that the switches should come off of the holes.

Take a PCB sheet and populate all micro switches on that according to holes drilled  on the front panel holes. For micro switches you should have to drill holes to accumulate all switches.

The switches should come out of the front panel like the image below when the key pad board is fixed in the front panel.

the rear side of the keypad board should look like the following after cabling and interconnection.

Here is another image for the above to show it a little more clearly. There is clearly shown the keypad and main board connections.

Testing:

Testing of the board is straight forward. We would have to supply the board with 220V AC mains on P and N lines marked on main PCB. This is sometimes mentioned on main PCB and sometimes one can do it with his or her understanding of the circuit if not clearly mentioned. Also there is one small jumper needed to tell the main PCB that the oven door is closed. That jumper is actually replacing the oven door switches which is an interlock for the oven to operate only in case when the oven door is shut. That jumper we will temporarily solder to the board and then after testing we will discard it.


Here is the 220V AC mains connection on the main PCB.

Here is the jumper soldered to the DOM terminals on the connector to translate the closed door interlock to the main PCB.

Here we are testing the system by pressing on the start 30 second button after powering the unit up. So the unit switched on and got 30 second command and started reverse counting when pressed on the button. In this way we will test all switches for proper functionality.

Hope this will help people having same problem with their microwave oven. Anyhow I am giving such service to make such modification if one is not able to do it. You can contact me for such modification if you are in need.

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