Heater Sparks Then Shuts Off

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Space Heater

Repair guides and support for small electric personal space heaters.

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Eddie Yeung @eddieyeung

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发帖于: 2018年3月16日

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Heater Sparks Then Shuts Off

I have a Noma brand heater model: AFH302OTW. I recently disassembled the housing to vacuum all the dust inside that had accumulated over many years. After I reassembled the housing, a problem occurred. The heater would run for a short period of time, then a spark would occur next to the heating coil and the unit shuts off on its own. The fan is working and there is heat from the heating coil before it shuts down. If I unplug the unit and let it cool, it would turn on again for a short while until it shuts off again. I presume something is overloaded that is causing the safety switch to kick in, but I am puzzled which part failed. Could it be a faulty temperature sensor?

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jayeff @jayeff

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Hi,

Here is an image taken from one of your images. ;-)

(click on image to enlarge for better viewing)

Just so there is a better view, if you can, by using a soft brush could you please clean the area in the red circle? (power disconnected of course)

Also is the heater element wire shown by the green arrow actually touching the metal strip below? It seems very close. If it is I don't think that it should be.

The connection shown in the yellow square, is it a dry joint wire? I don't particularly like seeing 'holes' when a wire is supposed to be terminated correctly

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See image after cleaning.

The heater element wire is not touching the metal strip. Sorry the angle of the photo made them appear touching.

Sorry not sure what you mean by dry joint wire.

由 Eddie Yeung 完成的 2018年3月17日

Hi,

A dry joint wire is when a wire has been incorrectly soldered to a connection point. Usually, in the case of a wire being passed through a hole and then soldered on the other side to a connection point, not only is the wire soldered onto the connection point but the hole through which it passes is also filled with solder. This prevents the wire from moving if the contact point of the wire becomes loose thereby maintaining an electrical connection. It is called a dry joint because the solder has not been applied correctly allowing the wire to potentially disconnect and open the circuit. Very frustrating to find as it may cause intermittent connections as the wire will move due to vibrations etc. Good connection one minute bad the next.

Although now that you've cleaned up the area (thank you) it appears that it wasn't what I thought .

I believe that @oldturkey03 is right and that there is a problem with the diodes, judging by the scorch marks on the pcb.

由 jayeff 完成的 2018年3月18日

So it's a diode failure that caused the spark and the safety switch to kick in? I guess I'll have to check the diodes. Thank you all for your helpful inputs!

由 Eddie Yeung 完成的 2018年3月18日

Eddie Yeung yes, it could have been the diodes but it can always be something else. At first you want to replace those (always order more than you think you need) and then check it out again.

由 oldturkey03 完成的 2018年3月18日

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See image after cleaning.

The heater element wire is not touching the metal strip. Sorry the angle of the photo made them appear touching.

Sorry not sure what you mean by dry joint wire. — Eddie Yeung
Hi,

A dry joint wire is when a wire has been incorrectly soldered to a connection point. Usually, in the case of a wire being passed through a hole and then soldered on the other side to a connection point, not only is the wire soldered onto the connection point but the hole through which it passes is also filled with solder. This prevents the wire from moving if the contact point of the wire becomes loose thereby maintaining an electrical connection. It is called a dry joint because the solder has not been applied correctly allowing the wire to potentially disconnect and open the circuit. Very frustrating to find as it may cause intermittent connections as the wire will move due to vibrations etc. Good connection one minute bad the next.

Although now that you've cleaned up the area (thank you) it appears that it wasn't what I thought .

I believe that @oldturkey03 is right and that there is a problem with the diodes, judging by the scorch marks on the pcb. — jayeff
So it's a diode failure that caused the spark and the safety switch to kick in? I guess I'll have to check the diodes. Thank you all for your helpful inputs! — Eddie Yeung
Eddie Yeung yes, it could have been the diodes but it can always be something else. At first you want to replace those (always order more than you think you need) and then check it out again. — oldturkey03

oldturkey03 @oldturkey03 声誉积分: 782.4千 1.1千 893 2.3千 · Answer 1 · 2018-03-16T20:22:02-07:00

oldturkey03 @oldturkey03

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Eddie Yeung this sounds like your limit thermostat is turning of the unit. Post some images of it disassembled so we can see what you see. Use this guide 在已经存在的问题里加入图片 for that

Eddie Yeung looks like the diodes (Zener diodes as well) have failed. Those are most likely part of the rectifier circuit for your heater. The only way to fix that would be by carefully desoldering those and take a look at them to identify which diodes these are. Again, do feel free to add images of those if you are having trouble identifying them.

On the same image that @jayeff pointed out, can you identify that there is a resistor or similar between the contacts?

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Eddie Yeung post some images of the PCB, specifically the one in your 1st picture bottom left of your heater.

由 oldturkey03 完成的 2018年3月17日

PCB photo added.

由 Eddie Yeung 完成的 2018年3月17日

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Space Heater

Heater Sparks Then Shuts Off

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Update (03/17/2018)

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