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[SOLVED] HotPoint Ariston Refrigerator Power/Control Board (NMBT 1912 F T/ha)

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e-music

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Hello everyone,

I bought this refrigerator from the 2nd hand market. It's been working fine until I realized that something is wrong with the defrost system. I had to manually turn it off for 5~8 hours from time to time to let the ice melt down in the freezer and allow air to circulate again into the fridge. I made some research on similar refrigerators and found that failures are very common on certain parts of its defrost system.

I have checked the resistance and it was giving the correct reading based on the electrical specs printed on the refrigerator. However, I found that there are two sensors and I was able to find one of them with bad reading when tested its resistance in cold water and compared it with a new one ordered recently. I have replaced both anyway!

Unfortunately, I forgot the power cord plugged (very stupid I know) while I was trying to replace the temperature sensor inside the freezer. I don't know, but looks like the sensor is powered directly from the AC rail and I still don't understand it and how its reading is obtained at the uC side. Perhaps an ADC through some discrete analog components are doing the bridging between the sensor and the uC on the board? The cable was cut and stripped off already because I wanted to take the old sensor apart for testing. I had a spark when the cable accidentally touched the copper line coming from the compressor. I have immediately realized then that I made a big stupid mistake and disconnected the power cord right away. When I have pulled out the control board, I found one trace (I believe the one coming from the connector that supplies power to the temperature sensor concerned) with solder mask removed as a result of the excessive heat from the short. The trace is still conductive, no physical damage has happened to any component on board. I checked all diodes, transistors, etc, everything seems fine. The PSU seems to work fine as well. However, the refrigerator is no longer starting up, the "On" button on front panel is no longer having light and is not responsive at all. When plugged into power again, the LCD shows blinking "28" after 2~3 minutes but refrigerator is dead.

I had no way to find a schematic, but there's a small block diagram printed on back of the unit. The unit is equipped with a protector/overload circuit. I don't know if the problem lies there or the problem is the control board itself. Control board costs almost half the cost of the price I paid for the whole unit itself. I can't order it blindly while I'm not sure whether it would solve the issue or not. Since the LCD blinks with "28", I have a feeling that this is coming from the control board and indicates an issue somewhere else. Unless the LCD module is programmed to show this error thing when it doesn't receive data from control board normally.

I hope someone has an advice that could help me figure it out.

Thank you all for your help!


Zaher
 

KlausST

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Hi,

First if all: The damage will be hard to find, maybe several parts a defective now, maybe it is irreparable.

And:
Nowadays we have a camera in every cellular phone, laptop.... why not simply take some photos and upload them here?
They are more objective and will tell a lot more than you are able to describe with a lot of text.

Klaus
 

e-music

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Hi Klaus,

Thank you. You were correct. I thought I would give a good description to the problem and will follow it up with some pics. Anyways, I have reassembled the board and the refrigerator is back to work again. I don't know if removing the LCD module for several days had anything to do about it, but looks like the LCD module still has a problem. I can't control temperature or other functions, but the refrigerator is working fine.

Regards,


Zaher
 

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