Smart Fridge Guard Trips

Dear Gurus,

I have smart fridge guard which had served me fantastic since 5 years but now it has started giving problem. Problem is that it instantly trips and disconnects mains power. I have tried adjusting 2 variables provided on circuit but no advantage.

All this happened after some weeks when its fuse wire was burnt and I re-soldered it. Can anyone help me what could be wrong and which part can be most likely culprit to be replaced?

Thanks.

mj1w84.jpg

14xyro6.jpg

1zn3d5t.jpg

s41f7t.jpg

It might be current sense mechanism instead of what you thought to be a fuse wire. If it is, shorting/resoldering it would make the device not operate as intended.

The sockets have burn marks so the circuit has probably been over taxed.

Thanks for replying Asad bro, Sorry I was away for Eid holidays... The board says the wire is acting as 5watts fuse. Actually it kept working for couple of weeks after resolder and then started tripping.

Any solution to this? Do I need to put a new wire altogether ?

Where does it say it is '5W fuse'?

What you refer to as a 5 Watt 'fuse' on the left side of the first photo is probably where a 5 Watt resistor should be - it appears that someone has replaced the resistor with a plain wire. The resistor should be part of the circuit that senses current (through voltage drop across it) and triggers a safety device. A plain wire would not have the voltage drop.

@Asad its in series with the 220V mains. and I have read somewhere that it can act as fuse...(have seen a small resistor in CFL circuit which acts as fuse)...

Its connected with mains wires as diagram below hence I think its acting as fuse...

220 --------------------------

220 ---------|\/\/\/\/\|--------

@F I think You are right about the 5w resistor which you showed in image but no one replace it with plain wire.. It was came like this since day 1 when I purchased it and it served me for almost 5 years without any issue.

What are the numbers of the two 7-8 pin ics visible in the picture? I need to how the circuit works?

Aurangzeb

I do not see a transformer anywhere on the PCB and these circuits cannot operate at 220 volts. It may be that missing 5 Watt resistor and blue capacitor (can you read its value?) plus some other nearby components (diode, black capacitor) formed a capacitive transformerless power supply for the circuit. I notice a number on the PCB but can you find supplier's name printed anywhere on PCB?

@aurangzebhaque bro below are the IC values

LM339N (GF83157b) images?q=tbn:ANd9GcT9MpQb0OrJZMX8b0FANO3(https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcT9MpQb0OrJZMX8b0FANO3RSlOW3Wx0_y-czxxjB2XNccxB9-ts3A)

HEF4093BP HEF4093BP.JPG(https://s3.amazonaws.com/Icarus/IMAGES/SM3/HEF4093BP.JPG)

@F bro yes this is transformer less circuit with a large capacitor and bridge circuit same as rechargeable LED lights have. Blue capacitor is 225J and 260volts. Black capacitor is 50v and 680uF. Number written on PCB is 100611 and KW1.. nothing else written on board. manufacturer is SMART which was a famous company producing fridge/ac protectors.

Thanks.

Also how did it work? Was there a lag of few minutes before power was available to the fridge, after WAPDA's return.

Look at all the big capacitors that you have mentioned. Are any of these leaking any fluid or look like they are swollen in the middle or top

Aurangzeb

Yes it has a delay timer. when there is a low or high voltage, say <= 170v or >=260v then it turns off supply to fridge and waits till voltage comes back in range. then it further waits for 2-3 minutes before supplying voltage to fridge.. Same happens if there is a brief short circuit or surge/spike in voltage

EDIT: capacitors are not leaking

Looking at overall damage to circuit board and housing, it would be better to buy a new commercially made device for Rs 700 such as Dolphin Refrigerator & Deep Freezer Protector (see www.dolphin.pk). Even if you reverse engineer and install all the missing / semi-damaged parts, repair broken/burnt PCB copper tracks and recalibrate the device to revert to original settings of both variable resistors, you can't be sure that no other hidden damage exists which can affect your fridge. Take the plunge, spend Rs 700 and retire the Smart Fridge Guard - it has served you well for five years. Don't risk burning out your fridge compressor and possibly starting a fire.

Yes bro I have already installed dolphin fridge protector last month. Got it for Rs. 650. I was just curious about this one to see if it can be brought back to life :) :)

It still operates but trips to protection mode as soon as connected to mains, even if there are 220v available so it means its sensing false under/over voltage and tripping to protect mode.

Can you check

1. If the diode next to the relay is ok.

2. The transistor driving the relay is ok.

You need to have a multimeter to do that.

Aurangzeb

I can check the diode but don't know how to test transistor. Can you please guide me? I have uni-t 203 meter.

Please take high resolution photo of the board top in which the details of the components are clearly visible so that we can take it fwd.

Aurangzeb

Ok dear. I will try to catch some high res images...