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Old 04-04-2020, 11:35 AM   #1
DanFen
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Default Troubleshooting Electric Blanket

This is an electric blanket, from the LIDL brand SilverCrest

Issue: Not working (of course, what else!)

First thing I noticed is that when I check the input voltage (which is AC, as there is no transformer in between) on the positive and negative of the wire that's connected directly to the board from the plug, it's measuring 2VAC ( I am attaching a photo and marking the AC in). PS. There's plenty of stuff going on on the other side of the board (although nothing looks burnt out). Just want to start from the basics

As a newbie, and for the learning purposes, the first question would be:

As a device (an electric blanket), does it need to change current from AC to DC? Are there devices that actually run on AC, and if there is, why is that?
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Last edited by DanFen; 04-04-2020 at 11:38 AM..
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Old 04-04-2020, 11:43 AM   #2
R_J
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Default Re: Troubleshooting Electric Blanket

If you only measure 2vac where the cord connects, don't you think the fault would be with the cord? or the plug?
The blanket element is supplied with ac also and controlled by the scr's
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Old 04-04-2020, 11:44 AM   #3
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Default Re: Troubleshooting Electric Blanket

unclip that board and see what's on the other side - and check the power cable for continuity.
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Old 04-04-2020, 11:52 AM   #4
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Default Re: Troubleshooting Electric Blanket

Sorry forgot to mention that I already desoldered the connections and tested the voltage directly, and it measured ~240.

Thanks for the explanation about the AC. Am I right to say that the SCRs are the two black components next to the caps?

Quote:
Originally Posted by R_J View Post
If you only measure 2vac where the cord connects, don't you think the fault would be with the cord? or the plug?
The blanket element is supplied with ac also and controlled by the scr's

Last edited by DanFen; 04-04-2020 at 12:01 PM..
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Old 04-04-2020, 11:57 AM   #5
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Default Re: Troubleshooting Electric Blanket

This is the other side. "There's plenty of stuff going on on the other side of the board" was a little bit exaggerated

EDIT: Pads on the top control the timer, pads on the bottom control the temperature.

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unclip that board and see what's on the other side - and check the power cable for continuity.
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Old 04-04-2020, 12:07 PM   #6
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Default Re: Troubleshooting Electric Blanket

Quote:
Originally Posted by DanFen View Post
Sorry forgot to mention that I already desoldered the connections and tested the voltage directly, and it measured ~240.

Thanks for the explanation about the AC. Am I right to say that the SCRs are the two black components next to the caps?
So your measurment in post #1 was wrong? and you do have 240vac across the two points with the arrows? If that is the case, check both fuses F1 and F2 (white) on the board. If they are ok, Check the voltage across C1 & C4. also check the resitance across the two wires going to the blanket, it could be the blanket element is open.

Last edited by R_J; 04-04-2020 at 12:11 PM..
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Old 04-04-2020, 12:08 PM   #7
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Default Re: Troubleshooting Electric Blanket

Gotta love how the live wires (240V) have been crushed, by the screws that hold the case together.


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Old 04-04-2020, 12:10 PM   #8
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Default Re: Troubleshooting Electric Blanket

Yeah noticed that too, on both sides actually :/

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Gotta love how the live wires (240V) have been crushed, by the screws that hold the case together.


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Old 04-04-2020, 12:14 PM   #9
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Default Re: Troubleshooting Electric Blanket

No, when I measure the voltage while connected to the board, it measures 2VAC, when I measure them outside of the circuit, they measure ~240VAC.

I will remove them again, cause I did this a week ago, and now I'm in doubt

F2 is OK. Is F1 a fuse or a resistor?

Quote:
Originally Posted by R_J View Post
So your measurment in post #1 was wrong? and you do have 240vac across the two points with the arrows? If that is the case, check both fuses F1 and F2 (white) on the board. If they are ok, check the resitance across the two wires going to the blanket, it could be the blanket element is open.
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Old 04-04-2020, 12:21 PM   #10
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Default Re: Troubleshooting Electric Blanket

Double checked. Ive' removed the connections out of the board and voltage is ~217VAC.

As soon as I solder the connections to the board again, and measure the VAC of the same connections as highlighted in my first photo, it measures 2VAC only.
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Old 04-04-2020, 12:28 PM   #11
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Default Re: Troubleshooting Electric Blanket

Your ac cord is open. There is no way the board is loading down 240vac! If it was your mains breaker would have blown.
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Old 04-04-2020, 12:31 PM   #12
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Default Re: Troubleshooting Electric Blanket

Can you please explain what "open" means? Not familiar with the term. Can't understand how it's possible to measure ~217VAC directly and then ~2VAC on when in circuit. I can't be that bad to be measuring wrong (or am I?)

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Your ac cord is open. There is no way the board is loading down 240vac! If it was your mains breaker would have blown.

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Old 04-04-2020, 12:40 PM   #13
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Default Re: Troubleshooting Electric Blanket

The cord is broken, the wire is not connecting between the a/c outlet and the board. Check the resitance of both wires in the cord.
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Old 04-04-2020, 12:48 PM   #14
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Default Re: Troubleshooting Electric Blanket

So this is the voltage measurement of the cord (i.e. from plug to meter).

I'll check the resistance. So I just have to remove the wiring from the plug itself and check each wire from one end to the other (for resistance), right?

EDIT: Resistance is 0 on both wires (I've zero'ed them out before measuring).
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File Type: jpg IMG_20200404_210129.jpg (395.9 KB, 4 views)
File Type: jpg IMG_20200404_210206.jpg (365.4 KB, 4 views)

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Old 04-04-2020, 01:06 PM   #15
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Default Re: Troubleshooting Electric Blanket

Quote:
Originally Posted by DanFen View Post
So this is the voltage measurement of the cord (i.e. from plug to meter).

I'll check the resistance. So I just have to remove the wiring from the plug itself and check each wire from one end to the other (for resistance), right?
Do you really think that little board is loading down the 240 volts coming out of the outlet?
Connect a light bulb to those wires and see if it lights up.

Last edited by R_J; 04-04-2020 at 01:08 PM..
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Old 04-04-2020, 01:22 PM   #16
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Default Re: Troubleshooting Electric Blanket

Good question as I said, I'm a newbie. If you say it's impossible then something tells me I'm measuring something wrong. Not sure what to tell you really

In the meantime, we have light. So this tells us that the wiring is fine right? I can solder the wiring back onto the board and measure voltage on the contacts again, unless there's anything else you'd suggest we test.

Quote:
Originally Posted by R_J View Post
Do you really think that little board is loading down the 240 volts coming out of the outlet?
Connect a light bulb to those wires and see if it lights up.
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Old 04-04-2020, 01:24 PM   #17
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Default Re: Troubleshooting Electric Blanket

The ac cord must be ok and your reading when connected to the board must be wrong. Did you check the fuses on the board?
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Old 04-04-2020, 01:26 PM   #18
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Default Re: Troubleshooting Electric Blanket

OK, in that case, my reading might be wrong then. I'll attach again to the board and try again.

F2 is fine (checked in continuity mode of course). F1... isn't that a resistor?

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Originally Posted by R_J View Post
The ac cord must be ok and your reading when connected to the board must be wrong. Did you check the fuses on the board?
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Old 04-04-2020, 01:30 PM   #19
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Default Re: Troubleshooting Electric Blanket

F1 is a thermal fuse. If should check like a short, if it does not, then it is open circuit. It can be jumped with a piece of wire ONLY TO TEST. then it MUST be replaced with a thermal fuse.

Last edited by R_J; 04-04-2020 at 01:36 PM..
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Old 04-04-2020, 01:38 PM   #20
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Default Re: Troubleshooting Electric Blanket

OK, now I have 220V on the connections (on the circuit). So, this confirms that my readings were wrong.

So F1 is the white one in between of the resistors right? If so, then yes it's good.

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F1 is a thermal fuse

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