Sears Garage Door Sensor Repair

[rmel]

Hi,

I'm trying to repair and understand a friend's garage door safety sensor.  The sensor is not working, as the garage door unit will not close and it just flashes the lamp.

It's a Sears Craftsman purchased around 1994, so it's pretty old.  This is the receiver portion, not the sender.  The circuit seems pretty simple, but I'm having trouble identifying a few components.   I'd appreciate any help identifying the IR sensor.

The only markings I can find are: 60 and S43.  It also has three pins, and I am having trouble finding an IR sensor with 3 pins.  Is it a diode or a phototransistor?  Something else?

Also, I think there are two transistors on the bottom, but I don't know how to translate the numbers on the package.  Based on testing them in-circuit, I think one is NPN and the other PNP.  Any idea if the markings on the package are usable in identifying them?  I think the NPN is marked H1 and the PNP is marked 213.

I've been looking at this thing for a week now, and I'm finding the operation of it pretty interesting, and I'd really like to understand how it works.

Any help with identifying the components would be a great help.

Thanks

[xrunner]

I've worked with phototransistors on my model railroad and they only have two pins, but I think some have three, even though the third pin doesn't really connect to anything.

I could be wrong though.

[C]

First you should know you can get replacement garage door safety sensor from many sources on the net.
Sears sold Lift-Master or Chamberlain brand openers. Start With a model number and other numbers you find printed on motor unit of the opener.

If you check the patient database you can find some details
For example some sears openers have just a lighted push button to open the door while others have a button to open the door and a button to turn on just the light. All just use two wires and if you have the fancy control it will probably work in place of just the push button. The difference between the open door button and turn light on button is just the proper value cap inline with the light switch button. And if you look the cap value is in the patent as well as how it works. 

Note that the newer openers may not be so simple.

I would guess that the three lead device is an IR Receiver like what is used in a tv.
The question is what IR light wave length and what modulation frequency if it is a IR Receiver.
Check
http://www.vishay.com/ir-receiver-modules/

C

[rmel]

Thanks for the responses.

The fact that the IR sensor is 3 pins is what's confusing me too.

I've already looked on ebay, and I've found some replacements that look pretty close to what I've got.  I may end up getting one of those, but I really am interested in learning more about how this works.  I will try to look up the patent on the unit.  That never occurred to me.

This has been pretty fun playing with this.  I've checked the signal on the scope and tried connecting the unit to the signal generator in order to try and replicate the behavior.  I can't say I've had too much success, but I'm learning a lot.

Thanks also for the links, I'll checkout that site and hopefully find something close.

[JoeO]

Did you check the IR transmitter with a camera to make sure that it is working?

[Mr Smiley]

looks like it uses all three pins so I’d say it was either a photo-transistor or an early 38khz ir module 

 

[rmel]

Did you check the IR transmitter with a camera to make sure that it is working?

Do you mean take a picture camera and point it at the output of the transmitter?  What would I see if the transmitter is working properly?

[rmel]

looks like it uses all three pins so I’d say it was either a photo-transistor or an early 38khz ir module 

 

I had looked through Digi-key for photo-transistors and all of them had two pins.  Same with the diodes.  I had never heard of the IR modules until C posted that link.  I found a couple where the pinouts could match what I see on the pcb (the output pin connects to the base of BJT).  This at least has given me more clues in understanding the circuit.

I found an old IR transmitter LED in my junk box.  I'm going to try and see if I can use it to turn on the sensor.

[NadAngel]

I think it is an IR module as pointed out before. They trigger on a modulated frequency usually 36 or 38 kHz. To verify, use an oscilloscope on the transmitter side. Probe the IR diode and if it is a IR module you should see a nice modulated signal in bursts with a carrier frequency of 36 or 38 kHz.

[JoeO]

Did you check the IR transmitter with a camera to make sure that it is working?

Do you mean take a picture camera and point it at the output of the transmitter?  What would I see if the transmitter is working properly?

If you view the transmitter with a cell phone camera or another type of camera, you should be able to see the IR led light up.

[rmel]

Thanks for the tip!  I'll give it a try.

[BWRX]

I think it is an IR module as pointed out before. They trigger on a modulated frequency usually 36 or 38 kHz. To verify, use an oscilloscope on the transmitter side. Probe the IR diode and if it is a IR module you should see a nice modulated signal in bursts with a carrier frequency of 36 or 38 kHz.

Not to resurrect an old topic, but it is definitely either a 36kHz or 38kHz IR module. Specifically, one like this from Vishay: http://www.vishay.com/docs/82745/tsop531.pdf

How do I know? The receiver module on my ancient Sears garage door system started malfunctioning due to the colder than usual temperatures, and I wanted to see if I could fix it for less than buying new sensors. The transmitter module is still functional but the receiver isn't. There aren't many components in the circuit, and it looks like the IR receiver is what bit the dust. I'll order a couple, swap it out, and report back just in case anyone else runs across this issue and doesn't want to buy an overpriced pair of new/used sensors.

[floobydust]

I find it's the electrolytic capacitors that are old and need replacing, and one had an weak old IR tx LED.

Vishay puts the marking code on the top; others on the front face under the bubble lens. OP would have to pull the shield, or find the TX carrier freq.
The big "S" may mean Sharp, who Vishay seems to have bought out the IR rx line.

[BWRX]

On circuits this old the electrolytic caps could certainly be suspect as well. The supply voltage looked ok on my sensors. The only markings on the receiver are in silkscreen on the rear - a "60" at the top and "S51" at the bottom. There are no markings on the component body under the green translucent lens/cover. The S most certainly means Sharp, but it's hard to track down the exact part number considering this was manufactured back in the early 90s.

I measured the IR emitter with a scope, and it's being pulsed by a 38.4kHz (averaged measurement) PWM signal, which is still within the peak sensitivity range of a 38kHz receiver. We'll see which of the Vishay IR receivers work with the original IR emitter. If none of them do I'll swap out the emitter for a TSAL6200 which is used to test the receivers.

[Armadillo]

Did you already diode mode check LED marked as D2?

[BWRX]

Yes, D2 is functional. It only lights up when the IR receiver is functional and receiving pulses from the emitter.

When the IR receiver output goes low it sinks current from the base of a PNP transistor. That PNP transistor sources current to the base of an NPN transistor. That NPN transistor pulls the positive supply line low which forward biases D2 at a low duty cycle. One of the Schottky diodes feeds the large electrolytic cap which supplies power to the IR receiver. That's how the NPN is able to pull the positive supply line low but doesn't short out the supply to the circuit.

If you wanted to bypass the safety sensor, which I wouldn't do, you just need to mimic the output pulse from the IR receiver by pulling the positive supply line low at the right frequency and duty cycle.

[Armadillo]

The key point is D2 provides the source current to the NPN transistor.

BUT if OP meant flashes the lamp to mean the LED D2 actually flashes, then the sensor circuit is working, then should look the fault at elsewhere.

Hi,

The sensor is not working, as the garage door unit will not close and it just flashes the lamp.

[Armadillo]

If you wanted to bypass the safety sensor,

Yes, it does look like broken light beam safety circuit for safety interlock. Maybe out of alignment.

[floobydust]

Since the door sensor performs a safety function, you want to detect open/closed door as well as open/shorted wiring or a dead/missing sensor.

These are basically one-wire systems with power+signal superimposed. There are many patents on garage door sensors and I'm not sure who Sears rebrands; Chamberlain, Wayne Dalton, Genie etc.

The garage light and open/close pushbutton switches can also be on the one-wire line, as a resistor swithced across the one-wire system. I think the MCU reads an A/D as well as looking for pulses there from the beam sensor. Other makes of garage door openers use another dedicated pair of wires just for the switches, to get around a patent.

[BWRX]

We'll see which of the Vishay IR receivers work with the original IR emitter. If none of them do I'll swap out the emitter for a TSAL6200 which is used to test the receivers.

The three IR receivers I ordered were TSOP53438, TSOP33438, and TSOP33338. The first two detect the emitted beam but don't activate long enough to work with the garage door opener. The 53438 and 33438 are looking for longer bursts, but the emitter in the Sears/Craftsman sensors is only providing a short burst. Fortunately, the TSOP33338 was designed for short bursts and works with the original emitter! The bottom line: if you have an old Sears/Craftsman receiver safety sensor that fails then chances are you could fix it by replacing this $1-2 IR receiver because the other components are less likely to fail.

Likewise, the emitter safety sensor could probably be fixed by replacing the IR emitter with a TSAL6200. Note that I didn't test this, but it's the emitter that was used to test the TSOP receivers.

[floobydust]

That's good news, TSOP33338 works as a replacement for $1.60

There are so many different modules and modulation/AGC schemes. Most of Vishay's lineup is for IR remote control use.
Only three parts are for light barriers or presence sensors, and 1-2m/3-6' range spec seems low.
The TSSP4038 seems to be another part that could work?

The Sears/Chamberlain 41A5034 sensor outputs a 600usec pulse train at ~160Hz.