Hi Les,
I suspect that the relay is normally closed and hence the circuit fails safe to powering the fridge on (so the food does not spoil) in the event of a failure on the board.
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Hi Les,As there is no 5 volts the relay could not be energised so I think the contacts may have welded together on the relay. (Unless thy are normaly closed contacts which is umlikely.)
Correct. I have removed the varistor from the board.............still 300 ohms.You have already measured the resisistance (In post #15) of the varistor by measuring the resistance between the tracks that went to the transformer primary. You said that the reading was 300 ohms
Yes, that is my opinion as wellThe board is just the 5 volt power supply and relay with a driver transistor
Yes the relay on the board is for driving the compressor. There is another connector on this board we are looking at which goes to the display board (situated in the freezer handle) where is shows the temperature on a digital display, and allows you to make it colder (or not so cold) It has an alarm and other things on it. None of that currently works because there is no 5 volts supplying it. Another plug (from our current board) goes to the light in the fridge (which works), and the remaining plug is for the Freezer Thermostat.In post#12 you say that the compressor still runs. I suspect that the relay on this board controls the power to the compressor.
This is a possibility. Or as you point out they are normally closed. Normally closed makes a lot of sense to me, because if the electronics burns out (as they have done), the freezer continues to work even though the compressor runs continuously. I am very grateful it is still running, because otherwise all my food would have been wasted ! From a security point of view I understand why you would argue it should be normally open, and you may well be correct. I currently have put the mains plug on a timer so that the compressor does not run 24 hours per day.so I think the contacts may have welded together on the relay
Yes I have done this............there is no resistance. The relay is either normally closed or the contacts have welded together.Can you measure the resistance between the square pad under the relay with 4 pins comming through it (Directly below the word plug of power plug.) and the track just to the right of it.
I have to take this board out every time I wish to look at it because it is under the bottom of the freezer and awkward to get to. I have to put it back when I have finished and connect 2 of the four plugs otherwise the compressor will not run. I have not been bothered to bridge the contacts as the wires (on the plugs) are short and awkward to get to. The plugs on the board I have to connect are the power (from the mains) which is CN3, and CN4 which goes to the compressor.Do not test the board out of the freezer unless you feel confident working on a board with open live mains on it.
Yes, you can confirm this by removing the varistor and measuring the resistance across it. If the reading is a short the varistor is faulty. In effect the varistor has sacrificed itself to protect the rest of the circuits.I understand that you believe it is the varistor which is faulty and needs changing.
Yes, that is correct. Just the same as you can drive your automobile without the seat belt on.Also, that I can remove the varistor, replace the burnt 5W100ΩJ, and it "should" work ? (Even though long term it is better to replace the varistor, it is OK to test the circuit without it) ?
Yes, but put a 1A fuse in the mains plug.with the transformer (230v to 6.6v) ...........can I connect the primary directly to the mains (with a fuse in the plug) and see if it gives an output of 6.6v AC (off the circuit board) ?
Have no fear.I am not sure if you can do this with no load..........that is why I ask.............will it spoil the transformer ?? if the transformer is working correctly, I do not wish to spoil it !
Yes. Be careful.can I connect the primary directly to the mains (with a fuse in the plug) and see if it gives an output of 6.6v AC (off the circuit board) ??
Great news- well done.I am glad to inform you that it now all works!
John, the 100R resistor must be left in circuit; it will not be damaged by the absence of the varistor.I have since removed the 5W100ΩJ from the board until I get a new varistor.
They are all the same- just sloppy adverts.I have a question please about the varistor.
Are all varistors with the reference 07D431K the same ?
On ebay I have come across some which say 07D431K................... 275Vac/350Vdc
and others
07D431K................... 430V ±10%
Yes..............for it to work properly I understand that the 5W100ΩJ must remain.John, the 100R resistor must be left in circuit; it will not be damaged by the absence of the varistor.
The way the adverts are written one has the impression that there are multiple voltages for the same reference 07D431K.They are all the same- just sloppy adverts
Very strangely, when this huge voltage spike happened and blew a lot of my electrical equipment, none of the fuses blew.That way a bad mains voltage spike will just blow the fuse.
Very strangely, when this huge voltage spike happened and blew a lot of my electrical equipment, none of the fuses blew.
My Pioneer HIFI has 2 fuses between the power cable and the transformer (all on the PCB board). Both fuses have not blown...........but the equipment is totally dead.
I'm pleased that the only things that are fauly are the 100 ohm resistor and the varistor. I think that this is a particularly good design as most things using varistors as protection just rely on a fuse blowing to limit the surge current which could be many tens of amps.
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