sunbeam electric blanket no heat

[jon5500]

Hi, Just joined this forum after trying to find troubleshooting info on my Sunbeam electric blanket. I don't know what's happened to these blankets. I've had at least three Sunbeam electric blankets and a Biddleford mattress heated cover over the last five years. None have lasted even one season. Sunbeam had a five year warranty and I went through it twice to get replacement blankets, but had to pay shipping each time which ended up costing half as much as the blanket, plus they started "dragging their feet" by the time I reached blanket #3. Growing up, I had a Sunbeam that worked well from my preteen years to college. Unfortunately, it was thrown out at some point.

Anyway, I currently have one unopened blanket, and another identical one that failed. Both have the same circuit board as shown in post #30 here. I swapped out controllers with a known good one and still weak or no heat on the failed blanket making me suspect the tiny circuit board as shown.

Today, if possible, I may try swapping out the resistors with the values shown as indicated here as well as the transistor IF someone can tell me what the number is? Looks like there was some uncertainty in that regard. Also, I have no SM components nor the set up for them so I was going to use 1/8 or 1/4 watt resistors and a standard transistor. Should work if I can fit into the case. IF it is determined that the transistor is just a 2907? (post 35), I have plenty of those in my bins (non-SM PN2907) but had hoped to be sure.

Thanks in advance for any responses.

 

[the great potato]

Hello, i couldn't tell you off hand any of the values. I gave up on fixing the blanket long ago. I baught a biddeford heated mattress pad at my local thrift shop, new still sealed in box for 2.99, at that price it was worth another shot at the heated bed items. But it's been working great now for over a year. I would still like to fix the blanket but that got tossed on a far off back burner for now. Best of luck with fixing it, would love to know what the issue is with these blankets, but i do suspect it to be the controller.

 

[jon5500]

Thanks. I tried the Biddeford pad and it too didn't last more than a few months. Hopefully, you've had better luck.

With my Sunbeams that have failed, the controllers I have swapped to brand new blankets and they worked fine. So I still suspect the tiny circuit board components mentioned here.

I may try the component replacement today and report back. I'll have to take a guess at the transistor, but will try the PN2907 and of course matching up any pinning difference to the SM equivalent. Worst case scenario will still be a dead blanket. I'll be using a variac and powering up slowly.

 

[the great potato]

Let us know what you find out. Lots of people have issues with these pads/ blankets. Not much answers to be found. Definitely let us know what you find and some pics would be great at the end. Best of luck! I can't break it if its already broke lol

Moderators note merged and corrected post

 

[jon5500]

No luck. I didn't have all the components, mainly lacking the 2907 transistor, so I substituted one less robust. First plug in all I got was the blinking controller with no settings allowed. Thinking I had messed up the wiring somehow, I rewired and flash, a puff of smoke and the transistor was burned. That's it for me, but anyone ever finishes this thread with a welcome solution and I'm sure many would be very thankful!

 

[the great potato]

Well thanks for the feedback! All you can do is try.

 

[jon5500]

Not quite done. I also own a Sunbeam throw that has the same circuit board within. This time, I ordered the correct components and they should be here in a few days. Will report successes/ failures at that time. Keeping fingers crossed. Throw also exhibits same loss of heat output over time so same symptoms as blanket.

 

[jon5500]

Today, I had a chance to desolder the tiny transistor and I have attached an image. I'm not sure if it belongs here or somewhere else, but I am trying to identify it and, if possible, cross reference it over to a non-smd unit. Thanks.

 

[73's de Edd]

Sir jon5500 . . . . . et al
That is going to be this family of unit . . . . and NOT the previously reference to a SMD . . . version of a lower voltage rated 2N2907.
Since the potential full AC voltage of the heating element string is going to be across / sampled by it.
PLUS I really believe that original unit will test out as GOOD,when being tested for its C-E avalanche / breakdown specs.
Help ME to help YOU . . . . by coming back with the units operating AC line voltage . . . . . 120 / or / 220/240 VAC ?
Also scour the unit and its paperwork for any Sunbeam PATENT numbers markings and give them.

http://www.s-manuals.com/pdf/datasheet/m/m/mmbta92,_mpsa92,_pzta92_fairchild.pdf

73's de Edd . . . . .

A clean desk is a sign of there being very-very-very cluttered desk drawers below it.

 

[jon5500]

Thanks, 73's de Edd. I began to suspect that the 2n2907 was not the transistor because I tried a spare one from my bin yesterday that I found and this time making sure I had wired it up correctly, but all I got was a blinking blanket controller on the high setting (blinking red). I then did a quick search with the SMD part number I had and also came across the much higher voltage transistor you mentioned in your post.

I'm attaching the blanket tag along with a close up to the patent numbers. I hope this is helpful.

 

[jon5500]

Just a quick update. The MPSA92 transistor arrived and I replaced the original with that one. The blanket is now working again, although, as before, heating is weak even at the highest setting. So, that module can definitely be ruled out. Not sure what else to do. I can switch out blanket controllers and even with a different one, heating is still weak. That only leaves the blanket itself. Maybe the heating wire resistance changes over time and the circuit responds by decreasing output. If so, then the buck stops here and nothing more can be done aside from a new blanket.

 

[Zrat77]

Hello I'm new to this conversation but I would like to add my wife just came home with a similar sunbeam electric blanket model with the same board in the blanket as this post has continued to discuss. After doing a thorough inspection and checking resistance, and evaluating each component thoroughly had came to the conclusion that something what's wrong with the transistor resistor array you because one time the numbers would all be right the next not and lo and behold one of the wires on the left side as it exits the board and goes through the tight junction between the two plastic pieces head force a break that when maneuver just correctly would give continuity and the proper resistance and with the slightest movement then would go back out of sink. A quick new crimp and a couple zip ties for strain relief I'm happy to report that the blanket is functioning 100% now. And thanks to all the fine folks that gave information and pointed in the right direction you made my task a whole lot easier.

 

[jon5500]

Are you talking about where the dual white wires exit out of the plastic module as seen here?

https://www.electronicspoint.com/fo...ic-blanket-no-heat.281560/page-2#post-1792804

If so, interesting and glad it worked for you. Unfortunately, mine never showed any lack of continuity throughout the system. Finally, I ended up rewiring it myself and using a different controller. Has worked great ever since.

 

[FearlessAmateur]

Are you talking about where the dual white wires exit out of the plastic module as seen here?

https://www.electronicspoint.com/fo...ic-blanket-no-heat.281560/page-2#post-1792804

If so, interesting and glad it worked for you. Unfortunately, mine never showed any lack of continuity throughout the system. Finally, I ended up rewiring it myself and using a different controller. Has worked great ever since.

I'd like to know how you did this if you're willing to share. I always figured the thing was fundamentally flawed and not worth slaving over in its current form, especially by someone of modest experience like myself. But I'd be game for an overhaul.

 

[jon5500]

I don't think I can. There was a lot of trial and error involved before finding a suitable working system. Basically, I sewed in a certain length of silver plated copper Teflon coated wire after first determining how much wattage I would need. I settled on a maximum of 100 watts. For the power supply, 12 VDC. The power supply has current limiting and that's how I vary power to the blanket. There is double fusing and short circuit protection. The power supply wires to the blanket are 12 ga ultra flexible silicone insulated wire.

Then there were temperature readings. I monitored those carefully and finally determined that 40 watts would be the continuous wattage, anything more would only be for warm ups and such. You'd be surprised at the amount of heat going through the wiring system. I like to keep wiring temperature under 150 F. As long as I use a warm blanket on top (I use a down throw), 40 watts is plenty for the coldest nights.

It took several weeks, but I finally had a blanket that's safe and will outlast any I ever bought in the past. You can google most of what I did. That's how I found out about design and any potential issues along the way.

An alternative is carbon heating tape. I didn't use it because the calculations were not clear to me, but there is a website that sells it and plenty of plans for making anything from electric blankets to heated gloves. Google it as I can't recall where it is.

 

[FearlessAmateur]

I don't think I can. There was a lot of trial and error involved before finding a suitable working system. Basically, I sewed in a certain length of silver plated copper Teflon coated wire after first determining how much wattage I would need. I settled on a maximum of 100 watts. For the power supply, 12 VDC. The power supply has current limiting and that's how I vary power to the blanket. There is double fusing and short circuit protection. The power supply wires to the blanket are 12 ga ultra flexible silicone insulated wire.

OK, thanks. I've been thinking the way around this is to bypass the complexity we managed to live without for decades, which seems to be what you've done, but at least you seem to have done it safely.

 

[jon5500]

You can also try looking for older electric blankets, provided they are safe. Oftentimes you can google that information. If you can't find anything about the blanket online, avoid it. The older Sunbeams, like the one I had 30+ years ago, lasted for at least two decades without trouble. It's a pretty hit and miss process though. I tried some older ones from eBay. None of them worked correctly, but you may have better luck with a thrift shop.

 

[2manylaptops]

I have the same blanket , I get 60 volts on each side with the voltmeter on AC across the two wires. The blanket side board.

 

[Jennyp]

I just happened to come across this forum and thought I should offer the following. I'm not sure of what exactly you all are thinking but then I don't know how old your blankets were. I had a Sunbeam electric blanket that was cranking out heat for 2 years then stopped. I fixed mine for $20.00. All Sunbeam electric blankets that I know of cone with a 5 yr. warranty. You do not need a receipt. I simply called them today up a return then mailed it in to them and they mailed me a brand new blanket for free. Then that one stopped working after 3 yrs and when I called them they wanted the info from the big tag on the blanket and the numbers on the bottom of the controller. With that they knew when it was manufactured and allowed 5 yrs. from that date. I guess with Covid maybe they didn't even want the old blanket mailed to them. They simply wanted a pic. of the controller wires cut up and blanket cut up a little and then sent me a new blanket for free. lol I'm rather good at electrical circuits but much preferred doing a warranty claim lol They seem to offer great customer service. If your blanket is over 5 yrs old I'd say you got your money's worth and just get a new one on sale. .

 

[Jennyp]

Typo correction. It should read "I simply called them to set up a return".