AC regulator problem/identify part

I got a heating pillow (for putting your feet inside it) that does not work.

Picture of the PCB:

And a schematic made by "reverse engineering":

I suspect the regulator (a BT169D) may be broken, but not sure. I plan to bypass it by a 1N4007 (in parallel with it) just to check. Suppose that would not do any harm.

But there is another component on the PCB which I'm not able to identify. It is the one in the schematic marked CBE 5T. I suspect it is some kind of diode, but not sure. Searching on internet gave no result.

Any suggestions what this component might be?

BTW, the values on the resistor in the schematic is based on measuring the resistors without removing them from the PCB.

The ‘regulator’, BT169D, is a thyristor, which is basically a triac that only conducts one way. The CBE5T is a type of diode I have not seen for at least 30 years and which I cannot remember the name of. As far as I can remember they break down at some pre-defined voltage to trigger the thyristor.

That must be a VERY old controller.

Given the age of the controller the heating pillow must be old too, and I would suggest, is not safe.

The heating pillow is one year old and has hardly been used. Got several and all the other is working fine.

Any suggestion about how to check the DBE5T diode and a replacement (in case it broken)?

The heating pillow is one year old and has hardly been used.

I'm surprised something that new uses a thyristor, I'd expect a triac for anything designed in the last 30 years.

Any suggestion about how to check the DBE5T diode and a replacement (in case it broken)?

I think they are called diacs, but I am not sure. I can't think how to test one, sorry. Hopefully someone more helpful than me will be along soon.

If you have several, have you tried board swapping?

aarg:
If you have several, have you tried board swapping?

No, I hope to fix this board. I know the pillow itself is OK, since I can measure the resistance in it. Beside, the LED is also dead indicating that the thyristor is not working (or the diac/diode does not work).

Guess the first test would be to bypass the thyristor by a diode - 1N4007 should work OK?

About not using triac - I suspect that it is to reduce the effect (by using only 50% of the AC power)?

Perhaps a DB3 diac can be used? If it is the diac that is faulty.

thehardwareman:
No, I hope to fix this board. I know the pillow itself is OK, since I can measure the resistance in it. Beside, the LED is also dead indicating that the thyristor is not working (or the diac/diode does not work).

Guess the first test would be to bypass the thyristor by a diode - 1N4007 should work OK?

About not using triac - I suspect that it is to reduce the effect (by using only 50% of the AC power)?

The idea behind the circuit is it is phase fired. It's how the heat is controlled. What bothers me is you have the AC in shunted by a 240 K resistor and LED in series. I would think the LED is a power indicator. I see the 1.5 Meg but with AC mains applied (120 ~ 240 VAC)? I don't see where it matters. A Google of "electric blanket triac circuits" will bring up hits of similar circuits.

Ron

Perhaps a DB3 diac can be used? If it is the diac that is faulty.

In the absence of anyone offering you a better answer and if you don't mind risking some smoke then I suggest you try replacing the thyristor and the diac as suggested. If it were mine I would replace the components, take it outside, plug it into an extension lead that was not plugged into the mains then plug it into the mains while keeping well back. Maybe it will work, maybe it will go bang.

Stay safe, do not touch while plugged in to the mains even if the switch is off.

Ron_Blain:
The idea behind the circuit is it is phase fired. It's how the heat is controlled. What bothers me is you have the AC in shunted by a 240 K resistor and LED in series. I would think the LED is a power indicator. I see the 1.5 Meg but with AC mains applied (120 ~ 240 VAC)? I don't see where it matters. A Google of "electric blanket triac circuits" will bring up hits of similar circuits.

Ron

The LED is a indicator. The intensity of the LED indicate how much power you have adjusted it to. The trim-potmeter has a knob for power adjustment.

Product link

Don't be a tease, please post the other side of the PCB for completeness.

thehardwareman:
the LED is also dead indicating that the thyristor is not working

Looking at your circuit diagram, I would have thought that the LED would light even if the thyristor is bust.
I'm sure you have inspected and tested the fuse, but have you checked the switch? Mechanical things can break.
Maybe check for continuity from the plug to the circuit side of the switch to exclude anything silly.

thehardwareman:
No, I hope to fix this board. I know the pillow itself is OK, since I can measure the resistance in it.

There are 3 wires to the heater, so two elements? Both have resistance?

[ BTW the circuit has absolutely no protection from mains transients, I would expect it to be prone to fail ]

thehardwareman:
The LED is a indicator. The intensity of the LED indicate how much power you have adjusted it to. The trim-potmeter has a knob for power adjustment.

So as drawn shouldn't the LED always be lit to some extent and it's dark? The fuse is good right and no obvious PCB cracks or breaks?

If you want just bypass the TRIAC (MT1 to MT2) and see if it makes heat. Very seldom have I seen a TRIAC fail open circuit and the same is true of the gate diac. Matter of fact you can short the diac and see if it makes heat but a diac also seldom fails open circuit. Don't know what the heating element resistance should be.

Ron

The CBE5T is a type of diode I have not seen for at least 30 years and which I cannot remember the name of.

Not that is matters but I believe it is / was called a DIAC. Was a bidirectional device that would hold off until a voltage was reached then turned on.

MarkT:
There are 3 wires to the heater, so two elements? Both have resistance?

[ BTW the circuit has absolutely no protection from mains transients, I would expect it to be prone to fail ]

I was surprised when I found three wires to the pillow. Yes, I can measure resistance between all three wires.

Perhaps I should connect it to AC and measure the voltage on the PCB board.

JohnRob:
Not that is matters but I believe it is / was called a DIAC. Was a bidirectional device that would hold off until a voltage was reached then turned on.

Pretty sure you are correct, when I first replied I could not remember what they were called. Not seen one for a very long time and I was surprised to see one in this circuit.

Looks very much as if blue to black is a thermostat.

Paul__B:
Looks very much as if blue to black is a thermostat.

Maybe not as each has resistance, its likely a centre-tapped heater resistance, to provide a lower voltage
for the trigger circuit. There may be a one-time thermal fuse in the element, but I wouldn't bet on it
given the rather shonky design.