Got a strange one for everyone today.

Backstory:

Had a remote for a TV go dead several months ago. Almost purchased another but decided to do something I normally would not bother with: troubleshoot the "dead" remote. Turned out: the IR LED (sender) was shorted (burned out). Replaced and remote worked fine.

Month later, same thing happened to ANOTHER remote that was nowhere near the first one. Discovered the IR LED was shorted. Replaced and worked just fine.

Couple months after THAT... once again - but even worse. Remote for my Denon disc player was dead - replaced IR LED. Now it works (sending data), BUT... the DVD player was not receiving any data. I hooked my oscilliscope up to the data out of the IR receiver on the DVD player and what would you know: no data was being received. Replaced the sensor (TL1838) and now it works.

Fast forward to this past week. I recently sold a Bose 3-2-1 system to a pal few months back. Everything was working fine until last week: he says the remote just stopped working. I check the remote and sure enough: sender IR LED is dead (shorted). Replace it and remote looks to be working (confirm it is sending data)... but just like my Denon... the 3-2-1 unit is not receiving any commands.

I suspect the receiver is burned out just as happened on my denon.

Here is the million dollar question: what the hell could be going on here? 3 different homes, multiple remotes.. Multiple receivers.. What could be burning them out like this????

I live in central Mexico (Hidalgo). I imagine it would have to be something environmental. I mean... in over 40 years I have almost NEVER seen a remote just go bad.. but now 4 in less than 6 months? And not just the senders - the receivers, too!!!

These are low-powered solid state devices that should last a lifetime. I would expect the rubber buttons to wear down before the IR LED's fail.

Is there something that all these situations could have in common?

The only possibility I could imagine is: poor-quality batteries? Maybe the cheaper no-name batteries are (at times) pushing more than 3v and that burns out the IR LED? If so - is it possible that an over-powered IR LED sender could ALSO burn out the IR receiver?

It is the same every time: the IR sender LED is a DEAD SHORT.

The part that really blows my mind is: the IR receiver, too! I know those go bad at times, but what are the odds of TWO going bad at the VERY SAME TIME that the remote also went bad? It HAS to be related somehow. This seems like too much of a coincidence.

Just trying to figure out what may be going on here... getting old repairing these remotes.

 

Hi,
i guess, nothing unusual. Probability theory. Once in 20 years it can happen

 

If things are as you describe, I can think of no explanation other than coincidence.

How did you determine that the LEDs were shorted?

 

If things are as you describe, I can think of no explanation other than coincidence.

How did you determine that the LEDs were shorted?

Removing the IR LED and applying low voltage (2v) with bench supply (current limited to 30ma)... Current maxes out, LED heats up.

Increasing to 60 or 80ma, LED just heats up more - no IR light is ever emmited. Attempting to increase voltage upwards of 3v makes no difference. LED is clearly shorted internally as it will draw 100% (CC) whatever current I set the supply to.

These IR illuminators typically only draw around 20-30ma. Even ones that can draw significantly more only NEED 20-30 in order to make IR light that can be detected with an IR detector.

-Dean

 

in fact, i never saw a shorted IR LED. IR LEDs degrade year after year and emit less and less light. However, the forward voltage is only slightly different from a good LED

 

An IR LED takes about 1.2 to 1.5V. To test for a short you should be using a lower voltage that.
The diode test in a multimeter comes to mind.

Did your shorted LEDs pass 30 mA in both directions? What was the voltage across them? If shorted, it would be close to zero.

 

I never bothered checking the current draw in both directions.

I also never bothered to check with a multi-meter. If a low powered LED does not produce light by 60-80ma but instead begins to heat up.. common sense says it is toast. Not sure why any additional testing would be warranted.

Yes, voltage across it was ZERO. When I initially tested the remote control, I not only looked for actual IR light to be emited, but also hooked the scope up across the LED leads to see if a signal was reaching it. Nothing. Nada, zip.

Upon removing the LED from each remote PCB, I noticed that AFTER it was removed, I got a signal at the solder pads. The LED was shorting out the circuit 100%. On the FIRST remote I noticed this issue on, my next step of diagnosis was: is my IR detector working and does the old LED in fact work with bench power?

I took a spare IR LED out of my bin (I purchased a 50-pack years back) and hooked it to my bench supply - limited to 30ma or so, w/ 2 volts. How I set the power supply: set the voltage to 2v, short the leads and set the current to 30ma. Please keep in mind - the voltage is not as important as the current is here. At 30ma, just about any low powered IR LED will emit light.

The new IR LED worked just fine: my detector instantly lit up. So that tells me my IR detector (just a IR receiver diode with a multimeter) works. It also tells me that the bench supply is set correctly to illuminate an IR LED.

Next step: I connect the OLD IR LED.. Nothing. After 30-45 seconds of being connected, I notice the leads getting warm. I check polarity - double check and tripple check. All good. The thing is heating up. It is not producing light. It is drawing constant current. The other (new) LED works just fine under the same test condition. I honestly did not bother testing it further with a multi-meter. Seems there was no point - the IR LED is obviously bad.

Install the new IR LED and now the remote works.

Same scenario 3 more times except: 2 of the other 3 instances now include not ONLY a burned out IR LED sender, but ALSO include a burned out IR LED receiver.

I tossed the old LED's already. And I have not bothered any diagnosis on the IR receivers other than test for VIN, GND and some data signal on the DATA line out pin.

In all 4 instances - the LEDs were not illuminating at all. When a perfect 3v was applied to each remote, no light was detected at the LED, no signal was found across the LED pins (using the scope). After replacement, light can be seen (using either camera or my IR detector), signal can be seen on the scope and voltage is seen across the pins by multimeter.

Obviously a bad LED in each case. Really did not see any use in testing for a short in reverse polarity, or with a multi-meter. Seemed pretty obvious each LED was internally shorted (drawing constand current, heating up and 0 volts across the pins). If there is some other phenomenon that I could have or should have perhaps tested for - I am certainly open to suggestions.

This is NOT my profession. I am the first to admit it. Been tinkering with this stuff for well over 20 years, but not a professional.

Bad LED aside... the crazy part is the ir receivers, too!!!

I have not yet received the Bose 3-2-1 unit back (should have it in a couple days), but I strongly suspect the same issue: the owner claims they purchased a compatible universal remote and THAT will not work either. Same issue I had w/ the Denon: my remote for the Denon amplifier (which also controls Denon DVD players) would not operate the DVD player - but controlled the Amp just fine. So after fixing the Denon remote, I replaced the 1838 IR Receiver and bam! Now both remotes operate the DVD player 100%.

As soon as I get the 3-2-1 in possession, I will program a spare Logitec Harmony remote (I know for a fact supports the 3-2-1 units) to the Bose 3-2-1 in order to see if the IR receiver is in fact dead. I may even plug up a spare 1838 receiver to an arduino and compare the received codes from the Harmony remote -vs- the original remote to ensure the commands are identical and being received just the same.

-Dean

 

A simple trick to “see” IR light is with any digital camera, including that on your mobile phone.
Silicon light sensors are very sensitive to IR light. Although the cameras have an efficient IR filter, some light is still captured.
In a darkened room, point your remote control to the camera itself and push any button, but I would suggest one that repeats like the volume control.
On a properly working receiver, you will see a faint but distinct flashing.

Side note; I would never, ever apply a power supply directly without a limiting resistor.
Even though it is current limited, the supply starts as a constant voltage, high current source. As it senses the low impedance, the control loop will change to constant current… but this will take perhaps 100 milliseconds or so, depending on the closed loop response. By that time however, your IR diode may be fubbed already.

 

Side note; I would never, ever apply a power supply directly without a limiting resistor.
Even though it is current limited, the supply starts as a constant voltage, high current source. As it senses the low impedance, the control loop will change to constant current… but this will take perhaps 100 milliseconds or so, depending on the closed loop response. By that time however, your IR diode may be fubbed already.

Duly noted, thanks for the heads up. Will be sure to include a resistor in the future.

For testing, I usually just use a simple IR receiver diode and confirm with my smart phone camera. With the cheaper IR LED's (the clear ones), you can often even see visible IR light with the naked eye. I also got somewhere a credit-card sized card that has IR-reflective material and shows the red light when a remote is pointed at it. I need to dig it out of the attic - been MIA for a couple years now.