Electric Blanket Repair - Perfect Fit Controller

[CDuncan]

In case someone else has a Perfect Fit blanket [not a Sunbeam product], Model LVBK-RF2 [power supply 120-18, and controller C-D7], I just repaired the controller. The controller just quit working, with the illumination LED behind the dial not coming on, nor the blanket heating up. I tried swapping the two controllers to the other blanket sides and confirmed the inop side worked with the good controller. That left the controller as the culprit.

Upon opening up, I couldn't find any overheat or other visually suspect controller components. I saw 18vdc from the transformer into the board and output of the regulator. I tried some freeze mist on the semiconductors, and even desoldered the base lead on all the transistors to check for open and shorts [B to C & B to E, reverse and forward biased] - - no problems found. The output MOSFET [International Rectifier, IRL2703P] was suspect because its output goes directly to one of the blanket leads. I thought that static electricity could have coupled from the heating grid wires directly into the MOSFET, which is ESD sensitive - - you can hear the crackling while making up the bed with the dry winter air. I ordered the MOSFET from Mouser Electronics for only $2.25 along with some of the other cheap transistors and op amp just to have all the bases covered.

Replacing the MOSFET fixed the problem. Hope this helps someone else with a similar problem.

 

[Valerie Lathrop]

Thank you profusely CDuncan for taking the time to post this solution.
Valerie

 

[Doc Hallenstein]

I ordered and replaced the MOSFET as you did and still no improvement. I push the on-off button, the red light comes on for about 4 seconds and then turns off. No voltage at the blanket termination. Stumped.

 

[Debbiewaugh1962]

In case someone else has a Perfect Fit blanket [not a Sunbeam product], Model LVBK-RF2 [power supply 120-18, and controller C-D7], I just repaired the controller. The controller just quit working, with the illumination LED behind the dial not coming on, nor the blanket heating up. I tried swapping the two controllers to the other blanket sides and confirmed the inop side worked with the good controller. That left the controller as the culprit.

Upon opening up, I couldn't find any overheat or other visually suspect controller components. I saw 18vdc from the transformer into the board and output of the regulator. I tried some freeze mist on the semiconductors, and even desoldered the base lead on all the transistors to check for open and shorts [B to C & B to E, reverse and forward biased] - - no problems found. The output MOSFET [International Rectifier, IRL2703P] was suspect because its output goes directly to one of the blanket leads. I thought that static electricity could have coupled from the heating grid wires directly into the MOSFET, which is ESD sensitive - - you can hear the crackling while making up the bed with the dry winter air. I ordered the MOSFET from Mouser Electronics for only $2.25 along with some of the other cheap transistors and op amp just to have all the bases covered.

Replacing the MOSFET fixed the problem. Hope this helps someone else with a similar problem.

Thanks so much for sharing. I was looking for hours about the controller and couldn't find anything until I found your article. Considering the company is out of business it is not easy to find any information.

 

[Debbiewaugh1962]

Thanks so much for sharing. I was looking for hours about the controller and couldn't find anything until I found your article. Considering the company is out of business it is not easy to find any information.

Could you please tell me where I could buy the fuse I can remember the name of it. Thanks

 

[73's de Edd]

Hel l l l l l l l l l l l o o o o o o o Debbiewaugh1962 . . . . . . ( now, won't that make you about 60 yrs of age ? )

I'm reading his post and nowhere do I read of a fuse being mentioned ?
Also this is the first E-blanket, that I would see being powered with an 18VDC power adapter . . . considering direct AC powered ones use 200-400 watts. Looking at the physical sizing that power pack @18 VDC I can see it PUSHING 5 amps as being a miracle to get a bare ~100watts.

. . . . . . . buy the fuse I can remember t . . . . . . .

. . . . . . . buy the fuse I ( can't ) remember t . . . . . . .


Also the typically logical place for any fuse being used would be associated with that power block.
My eagle eye, in its looking over that boards component side reveals, no potentially used olive green pigtail micro fuse . . . anywhere.

With no probable CDuncan comeback . . . . expecting any help from us would be further dependent upon :
1. Give us all of the voltage-current-wattage specs on that power block.
2. I see 2 pairs of white wires coming from the power block . . . . but can't see how they are connecting into the temp controller block
and they then should route out of it , and then pass over to the photographed controller PCB.

Once over to the controller board, code colored tubing slip overs are getting the RED and BLUE towards the POWER Mosfet circuitry.
Simultaneously the BLACK and WHITE leads I would see as going to the power adjusting SCR, which he relates to as being a
" voltage regulator " m m m m m m m m sorta' . . . . . to feed the adjusted level of power to the blankets heating filaments.
Then the paralleled pairs of .22 ohm resistors would be in series in the power loop to feed back current pull of the system to U101 or U103.

FACTOID . . . . . : SOMEHOW ? there is even being a small Cadmium Sulfide photocell at the bottom left corner . . .with its black extended . leads
ALSO as good of a photo as is the component side . . . . would also be required of the foil side of the controller board.
PLUS . . . . . do you . . . or a noble assistant . . .have any technical acumen ?
Question ? . . . . . is the identification on the 14 pin U101 able to be read . . . . or have they sprayed flat black paint over it ?

Thaaaaasssit . . . . .

73's de Edd . . . . .

Today's degree of development of Artificial Intelligence is being absolutely phenomenal, but then, its being no match for natural stupidity.

This was found . . . . confirming only 3.5A output . . . if this is being the same unit. . . . probably is.


.

 

[normd1954]

Any idea as to the function of the photocell on the side of the controller?

 

[CDuncan]

Any idea as to the function of the photocell on the side of the controller?

I believe it turns on (or dims) the LED that illuminates the dial number setting for night readability.

 

[normd1954]

I believe it turns on (or dims) the LED that illuminates the dial number setting for night readability.

Thanks. I believe you are correct.

 

[normd1954]

Any other ideas on how to fix these controllers. I replaced the main MOSFET and the controller turns on briefly and then off. The MOSFET tested bad.

How can one test without being connected to the blanket? How does the controller monitor the temperature - what is the feedback loop. What part should I throw at it next?

 

[73's de Edd]

How 'bouts one of youse whuts got one of those torn down, giving a GOOD full size photo shot of the foil side of its board .
Then foil tracing will reveal the power routing. . . . . until I see that, I can only expect temp referencing to be related to the state of heating element nichrome resistance.

 

[roughshawd]

I ordered and replaced the MOSFET as you did and still no improvement. I push the on-off button, the red light comes on for about 4 seconds and then turns off. No voltage at the blanket termination. Stumped.

Hey doc. These new electronics boards are micro-minitureized and don't use a standard signal to drive them. If(I repeat IF) you are older, it sometimes takes a few hours for the circuit to completetly boot before it will work, so plug it in, turn it on and come back in a few hours. Usually the light is on and you go, "wow... I forgot I was testing this dumb foot warmer..." or"...crock pot" or "...control board" or what ever... just saying. The next lesson in modern electronics is also pertinent to older electronics... "If... or When, a device fails(device being a component or diode or part of the device) other things could also fail" but generally, this new equipment is fairly stable meaning it isn't supposed to fail at all. The best way to fix this important stuff, is just to replace it with a cheaper, more stable deviceof the same type. It doesn't even have to be the same kind!!!!