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Electronics => Repair => Topic started by: sdancer75 on July 17, 2023, 05:35:54 pm

Title: Remote control IR diode's resistor value
Post by: sdancer75 on July 17, 2023, 05:35:54 pm
What should be the protection resistor R1 value of the IR diode of a remote control.

Title: Re: Remote control IR diode's resistor value
Post by: Twoflower on July 17, 2023, 06:04:17 pm
It looks like that no resistor is required and the pads are connected by a PCB-Trace. Can you measure the resistance between the R1 pads?

As the remotes usually use very short pulses the battery + transistor internal resistance is enough to not damage the LED. Plus over lifetime of the remote the LED is active maybe only in the range of minutes.
Title: Re: Remote control IR diode's resistor value
Post by: fant on July 17, 2023, 08:23:56 pm
If battery voltage is 3 V, usually it span from 1 to 1,8 Ohm.

Mandi
Title: Re: Remote control IR diode's resistor value
Post by: sdancer75 on July 18, 2023, 06:17:53 am
Quote from: Twoflower on July 17, 2023, 06:04:17 pm
It looks like that no resistor is required and the pads are connected by a PCB-Trace. Can you measure the resistance between the R1 pads?

As the remotes usually use very short pulses the battery + transistor internal resistance is enough to not damage the LED. Plus over lifetime of the remote the LED is active maybe only in the range of minutes.

The resistance between R1 pads seems to be infinitely....  I will recheck it. The pads oxidized because water dropped, and I cleaned them with isopropyl alcohol.
I will measure them again and I will let you know.
Title: Re: Remote control IR diode's resistor value
Post by: Twoflower on July 18, 2023, 06:26:47 am
It is hard to see on that picture (even if the images have very good quality) if the traces are corroded away. Especially the trace to the pad close to the 1 of R1 looks suspicious. Probably it‘s a good idea to check the traces and pads that are not protected by the soldermask closely.

It would be very odd if a resistor disappears leaving no traces. And the pads don‘t look like there was a part soldered.
Title: Re: Remote control IR diode's resistor value
Post by: Shonky on July 18, 2023, 06:32:04 am
Definitely not fitted by default from those pictures. Check for continuity from either side of the resistor and bridge if there is none - looks like near the 1 in R1 there is no track.
Title: Re: Remote control IR diode's resistor value
Post by: sdancer75 on July 18, 2023, 06:10:55 pm
The continuity between pads was problematic. Using my microscope, I noticed that both pads were discontinued from their main rails left and right,  by the oxidation they had. So, shortcutting externally the two points resolved the problem. Remote control works again.

Thanks to all guys.