Another little problem

[dustinpruente]

i noticed my stereo remote wasnt working right lately, i checked the voltage that led up to the infrared emitter and it was normal for a remote. my only conclusion that i can come up with is the ir diode is shot. is this possible, and if so, where can i find a replacement and does it have to meet up to the EXACT specifications as the original?

 

[Exo]

Any normal remote IR emitting diode should work...

 

[Nigel Goodwin]

i noticed my stereo remote wasnt working right lately, i checked the voltage that led up to the infrared emitter and it was normal for a remote. my only conclusion that i can come up with is the ir diode is shot. is this possible, and if so, where can i find a replacement and does it have to meet up to the EXACT specifications as the original?

There are a number of things that can go wrong in a remote control, the IR LED is only one of them. But it's VERY! easy to test - just check the voltage on either end of it, one end should go to HT, and the other to the driver transistor. There will also be a series resistor, but the voltage across the LED should be between one and two volts.

The failure mode of IR LED's is invariably that they go open circuit, where you will measure the full battery voltage across the LED.

One extremely common fault is dry joints (due to the remote getting dropped), these are usually on the LED, the crystal (or resonator), or the smoothing electrolytic.

 

[goodpickles]

Nigel- You are talking about continuity right? Wouldn't the test procedure be the same as for a diode?

 

[dustinpruente]

ive dropped this remote in the area of about 500 thousand times in the last month. maybe ill just get another IR diode and be done with it. the construction of the remote is fine. it works great up to the point of the diode, so i must need a diode. Nigel, what are you talking about when you said one end should go to the HT. what is the ht. i have little experience with IR and Remotes, i specialize in radio control.

 

[Nigel Goodwin]

Nigel- You are talking about continuity right? Wouldn't the test procedure be the same as for a diode?

Yes, but the higher voltage drop of an LED may cause problems with some meters - in the remote it's already connected to a suitable supply, and you can test it in circuit on a volts range - to be sure with a continuity test you would need to remove it from the board.

The other advantage of testing it with a voltmeter is that you are testing it under load, it may pass a continuity test, but fail under load - which is usually about 1A pulses!.

As a TV service engineer I see a lot of duff remotes, I don't recall ever testing an IR LED on an ohms range.

 

[Nigel Goodwin]

ive dropped this remote in the area of about 500 thousand times in the last month. maybe ill just get another IR diode and be done with it. the construction of the remote is fine. it works great up to the point of the diode, so i must need a diode. Nigel, what are you talking about when you said one end should go to the HT. what is the ht. i have little experience with IR and Remotes, i specialize in radio control.

HT is the supply voltage, it comes from the old valve days where it stood for 'High Tension', but it's been used since for the main power supply rail in transistorised equipment.

If you have a camcorder, webcam, or digital camera, point the remote control at it, they are all sensitive to IR and you should see the LED flashing.

 

[samcheetah]

Yes, but the higher voltage drop of an LED may cause problems with some meters - in the remote it's already connected to a suitable supply, and you can test it in circuit on a volts range - to be sure with a continuity test you would need to remove it from the board.

The other advantage of testing it with a voltmeter is that you are testing it under load, it may pass a continuity test, but fail under load - which is usually about 1A pulses!.

As a TV service engineer I see a lot of duff remotes, I don't recall ever testing an IR LED on an ohms range.

thanx for telling this Nigel. ive been into a bit of problem due to an LED and i was checking it on the ohms range. and it just kept telling me that the resistance is out-of-range. the voltmeter method is good. ill note this and whenever i get into testing an LED ill use this method.

should i do this with normal diodes too?? i mean they have a low voltage drop so i dont think there would be a problem with measuring it on the ohms range. altho i have a doubt that the current drain will be alot. am i right? because i dont want to flat my multimeter battery just because of checking a diode :lol:

 

[Nigel Goodwin]

Yes, but the higher voltage drop of an LED may cause problems with some meters - in the remote it's already connected to a suitable supply, and you can test it in circuit on a volts range - to be sure with a continuity test you would need to remove it from the board.

The other advantage of testing it with a voltmeter is that you are testing it under load, it may pass a continuity test, but fail under load - which is usually about 1A pulses!.

As a TV service engineer I see a lot of duff remotes, I don't recall ever testing an IR LED on an ohms range.

thanx for telling this Nigel. ive been into a bit of problem due to an LED and i was checking it on the ohms range. and it just kept telling me that the resistance is out-of-range. the voltmeter method is good. ill note this and whenever i get into testing an LED ill use this method.

should i do this with normal diodes too?? i mean they have a low voltage drop so i dont think there would be a problem with measuring it on the ohms range. altho i have a doubt that the current drain will be alot. am i right? because i dont want to flat my multimeter battery just because of checking a diode :lol:

If it's a digital meter it will probably have a diode testing range, it can't take any more current from the meter than the meter is designed to give, it will take most with the probes shorted together - but probably only a few milliamps.

If you're going to test diodes (or LED's) with a voltmeter, don't forget to feed the diode via a series resistor to limit the current, then measure the voltage directly across the diode.