sunbeam electric blanket no heat

[the great potato]

Ok for the pnp red lead on the top collector and blak to the left base reading is 958, and then black to right emitter 1455. I checked my instructions for my meter and I think I did it right.

 

[73's de Edd]

Ok for the pnp red lead on the top collector and blak to the left base reading is 958

Keep the Black to the base and swing the RED between the collector and emitter for taking the two readings.

 

[the great potato]

O ok. I'll get that and post back thanks for the info

 

[the great potato]

ok guys sorry it took a bit to get these readings, been really busy.. but ok With the black on the base, from the top collector i got 1060-1061 and from the emitter 1048 -1051.

 

[73's de Edd]

.

Sir Potato . . . . .

That tested junction voltage is somewhat higher that the range that I specified / expected , but at least its suggestive of good junctions.
Possibly they are using dual junctions to enhance thermal sensitivity, but its undefined on the degree of reliance upon the change of thermal resistance of the PTC wire that is making up the Muuuuuuultiple heating strands of the blanket in relationship to the thermal sensitivity of the Q1 transistor junctions.

Going back to the resistances of the 3 surface mount resistors, I was expecting an unknown error value being introduced by the heating wire cluster being shunted across series arrranged R14 and R15.
It is not reflected by those readings, unless there is a problem in that cluster of heating wires. .
Now is the time where the earlier requested resistances . . . . of my POST 18 is needed.
I just assigned 4 random id's to the 4 leads that route out to the heater wires as . . . . . . Top Left---Top Right---Bottom Left and Bottom Right.

Referencing to the very bottom illustration, you see the yet to be answered ? references:
1 . . . . .Is there being just the low resistance of a connecting wire from TL to BL
2 . . . . . Same info . . . but being relevant to TR to BR
3 . . . . .What is the resistance (of the blanket heating wires) that is being read from TL to TR and BL to BR
Take note of the area where I have drawn in a connective BROWN wire across the bottom of the
center drawings temp controller.
Can you take ohmmeter in hand and confirm if that direct connection is valid, with it going from the LN (wide blade of the AC plug) to the Q1 emitter / or / BR.


CLUSTER OF TECHNO REFERENCES:

73s de Edd

 

[the great potato]

Hello ill try to get those numbers posted for you tomorrow. Thank you much for your layout, so I can follow it easily. love the hail potato pic lol good show!!

 

[the great potato]

well hello all again !! sorry ive been away and very busy. But i decided to try something new to solve my Having to climb in to a freezing cold bed on snowy nights, besides fixing the blanket, and so far its worked great and its very safe and simple !! All i did was got a fleece blanket and put that on the bed, and you sleep on top of it. It dont get cold at all and when you lay down you feel none of the cold from the bed and from having two sides of insulation you get warm very quickly. So it really is a very simple low tech solution that has worked great ! We had one or two nights it was - 6 F and the blanket thing still worked great, so ive moved to work on my doorbell delay system rather than dealing with the crappy sunbeam blanket. LOL but i really do appreciate everything everyone helped me with. thank you all so much =)

 

[Pompey]

Hi Edd, I'm not the OP but I do have the same problem. Your photos and schematic are great.

I've confirmed that the Controller is OK by plugging a second blanket into it, and it works fine. I've also checked the wire connections and PCB inside the faulty blanket - seem OK.

Where I see unexpected values are in measuring the heating element.

BL - TL, and TR - BR are each about 23 ohms. Reasonable for a full size blanket?

But BL - BR and TL -TR are ~520 ohms at room temperature. Since this blanket is marked
as 180 watts I think I'd expect something like 100 ohms, and the 'good' blanket is in this range.

Thoughts or suggestions as to cause and/or fix? I can't figure an explanation for the
observed values....

Chris

 

[Bluejets]

Good example of electronic control gone mad. I can remember when an electric blanket used 2 elements and simple 3 heat switching.

 

[OCD Repair Guy]

We will be interested in the small sensor board in your #23 photo of your post #7.
Have the board disconnected from the plug that it normally goes into, and then go into your meters OHMS mode and test for the SMD resistors values as being

22,000 ohms
1500 ohms
62000 ohms
Realize that we will then have to take a little foil slice out between R14 and R15, for correcting of shunted readings, and then solder bridge the gap later.


Also . . . whilst you gots ye olde ohmmeter warmed up and running good . . . . test for resistance of all possible resistance connections of the

PCBs central 2 Top and 2 Bottom tabs:

TL to TR
TL to BL
TL to BR

TR to BL
TR to BR

BL to BR


And then use DIODE test mode of the DVM for checking out the junctions of the PNP transistor Q1.
Collector is the sole tab at the top near the Q1 symbolization
Base is the bottom left tab
Emitter is bottom right tab
Expect in the range of ~500------ 800 millivolts for good junctions.

73's de Edd

Hi 73's de Edd - I just signed up because I really appreciate the quality of assistance you were giving "the great potato" in this thread. It's a shame he pooped out before you could diagnose his problem, but I'm having a very similar problem so perhaps we can complete the analysis for others who have the same kind of problem (which is very common with these Sunbeam heated mattress pads apparently).

I'm helping out a classy old guy I know who's on a tight fixed income - his controller started blinking last week and it's starting to get cold at night so I checked it out and I thought the controller had gone bad because I got resistance readings across all three pins on the mattress pad coupling. I didn't know there was a circuit board inside of the mattress pad until the new controller arrived today and gave us the same blinking condition, prompting me to delve deeper and open up the plastic housing to see the circuit board in your photograph:


Without cutting the foil between R14 and R15 I got very similar readings as "the great potato"

R13 - resistor 223 - 20K Ohms [the great potato reading: 21.4 Ohms (he probably meant 21.4K Ohms)]
R14 - resistor 623 - 68.7 Ohms [the great potato reading: 60.2 (+/- .3) Ohms]
R15 - resistor 152 - 1.5 Ohms [the great potato reading: 1.5 Ohms]

Which is baffling, because the numbers on those resistors should be the values that you anticipated:

R13 - resistor 223 - should be 22K Ohms
R14 - resistor 623 - should be 62K Ohms
R15 - resistor 152 - should be 1.5K Ohms

I don't understand why all of the readings are so far off from the resistance codes on the parts...but fairly consistent between my readings and "the great potato" readings. Is there an alternative resistance code format for SMD resistors?

I've also taken resistance readings across all three pins and found:

Resistance across P1 and P2 = 20.08K Ohms
Resistance across P2 and P3 = 65.4 Ohms
Resistance across P1 and P3 = 20.04K Ohms

I've been looking around but I can't find any schematics or service manuals for this Sunbeam heated mattress pad, so I don't know what those values should be across the three pins (and it would be nice to know exactly what the values of R13-R15 should be too).

But I really want to fix this heating mattress pad for this guy because he can't afford a new one and this one is less than two years old, and I feel bad that he already paid for a new controller that he didn't need.

Any help is much appreciated.

 

[davenn]

I don't understand why all of the readings are so far off from the resistance codes on the parts...but fairly consistent between my readings and "the great potato" readings. Is there an alternative resistance code format for SMD resistors?

Probably because other things were connected to the board that are altering the measurements

 

[OCD Repair Guy]

Probably because other things were connected to the board that are altering the measurements

Thank you - that makes sense. I don't see another path for the meter voltage other than through the R13 resistor, so that reading must be accurate, but there's an alternate pathway through the transistor when I try to measure R14 and R15, so those are probably very inaccurate. I suppose I'll have to unsolder them from the board to get accurate readings. I'll go his place tomorrow and do that.

The similarities between my readings and "the great potato" readings makes me think that the resistors are probably not the problem though. I think somebody said that there's a heat sensor somewhere in the mattress pad (I don't recall coming across one when I looked it over for damage though); maybe that's what's faulty.

 

[OCD Repair Guy]

Keep the Black to the base and swing the RED between the collector and emitter for taking the two readings.

Thank you for explaining the correct procedure!

The code on this transistor appears to be "2D K" (but that "D" may be a "0" - it's so tiny that it's hard to tell).

The weird thing is, in diode testing mode my Fluke 11 Multimeter is giving a collector reading of .017 and an emitter reading of .001...and the exact same readings when I have the red or the black probe on the base. I don't understand how that's possible. I assume that this is the bad component, since diodes should only permit current in one direction, right? I removed the transistor from the circuit board and I'm still getting those same readings.

Also, I unsoldered the resistors from the board and got the correct readings this time:

R15 - 152 = 1.508K Ohms
R14 - 623 = 61.1K Ohms
R13 - 223 = 20.0K Ohms

R13 looks kinda low but I dunno if that's a significant problem.

Does anyone have any suggestions for figuring out how to find the right PNP transitor to replace the bad one in this circuit?

 

[FearlessAmateur]

Glad to see this discussion continues because my wife hasn't been happy with replacements for the same type of Sunbeam heated throw. I'm working with an ancient analog multimeter so have little to contribute pending delivery of my fluke 117, but to note that I had continuity across two of the pins (N and H) but not the third (BS). I measured a similar old Sunbeam blanket, and that third pin read high resistance but not an open circuit. On the bad blanket's board in the photo, however, I'm reading the same high resistance between the two terminals of the left-hand wire that I got from the pins of the working blanket. Does that implicate the board that everyone is focusing on? (I did notice the broken insulation on that wire and thought it would be an easy fix initially, but I doubt that's the issue.)

 

[Tha fios agaibh]

Does anyone have any suggestions for figuring out how to find the right PNP transitor to replace the bad one in this circuit?

look up smd code, get datasheet, match specs to similar component.
I believe its a THC2907A which is obsolete.
This substitute should work.

https://www.mouser.com/ProductDetai...=sGAEpiMZZMshyDBzk1/Wi/PUgtclNldl4S7KB919sxY=

 

[Alec_t]

I did notice the broken insulation on that wire and thought it would be an easy fix initially, but I doubt that's the issue.

It definitely needs fixing. With the insulation that badly damaged it's possible the internal wires have fractured.

 

[FearlessAmateur]

It definitely needs fixing. With the insulation that badly damaged it's possible the internal wires have fractured.

No question, I'm going to tend to it. It's only because I'm getting a reading from the wire terminals that I'm not getting from the connector pins that I suspect something's amiss on the board, as seems to be the case for so many other Sunbeam 'victims.' Will report back if I learn more. Thanks.

 

[em17976]

Hi,
Did you ever have any success with the blanket? I have the same problem and I am sure I am not by myself.

Thanks for your time,

 

[73's de Edd]

Sir em17976 . . . . . .et al

Any chance that your SUNBEAM unit is being Model 71660, if not give its model number and any US patent humbers given on the unit.
Also, how much of an approximation, is this units schematic to your unit ?

Particularly . . . . . does it seem to use a small mechanical relay K1 WHICH might be quasi-hidden by the didplay unit mounted above it at a slant at the top end of the units board.

Also the very separate small board with the Q1-R14-R15-R13 heating wires failure sensing circuitry.

Along with there being two small SCRs on the separate control board. . . . display board . . .probably, being in small TO-92 plastic cases.

SUSPICIONED PERTINENT SUNBEAM SCHEMATIC . . . . .




73's de Edd . . . . .


I just got myself a new bathroom scale, I found one that tracks not only weight, but also body fat, bone mass, and water percentage.
Gee . . . . . NOW . . . . I AM really depressed . . . in 4 different ways.

 

[the great potato]

Hi,
Did you ever have any success with the blanket? I have the same problem and I am sure I am not by myself.

Thanks for your time,

No, never got it to work. Gave up and bought a diffrent brand. Its the kind that gos under the sheet. And so far worked well for a few months so far. Sorry i just got back to ya, been busy. And sorry i couldn't be more help.