ir z probe for 3d printer repairing smd ir leds

[amateur_24]

Hi
I have a duet3d ir probe, I think at some point i may have shorted the board to gnd.
The leds are no longer working. I checked with my smartphone camera.
I have two questions:

1) I probed the led and found the drive signal. I assume the micro is working ok? no blown pins?

2)is it possible to replace the ir leds using either soldering iron or a hot air gun but without solder paste? Or would solder paste be essential? I know solder paste is how to do it properly.

Duet mini IR Probe

Looking for an automatic bed levelling system? Duet’s Differential Height Sensor board is a great solution for the Duet 3D range of 3D printer controller boards.

e3d-online.com

 

[rjenkinsgb]

With a simple component, you can replace them with a soldering iron, just keep heating the connections alternately until you can flick it off the board.

Clean the pads with solder wick, position the new part & hold it down with eg. a cocktail stick, then solder one of the terminals.

Verify the position is correct & if so, hold it down and solder the other lead(s).
(Or remove it, re-clean and reposition it).

 

[amateur_24]

Hmm it still doesn't work. I did think I may have the led backwards but after struggling for ages to solder it down, I relised the led can only go one way because the pads are only on the back and bottom.

I connected it to the scope, I could see the drive signal on the terminal on the front of the led so it would appear to have soldered down properly. I checked in continuity mode that the led cathode was connected to gnd.

are they easily damaged by excess heat? I am still very green when it comes to smd. I am just slow.

here's the schematic for the board

OrmerodSensorBoard/SchematicAndPCB/Mini-differential-IR/V1.2/schematic.png at master · dc42/OrmerodSensorBoard

Z-height sensor board add-on for RepRapPro Ormerod 3D printer - dc42/OrmerodSensorBoard

github.com

where i got the leds from

SFH 4045N ams OSRAM, CHIP LED 950nm IR LED, Side View SMD package | RS

uk.rs-online.com

 

[rjenkinsgb]

It is possible that excess heat could damage them, especially if there is also any physical stress on the package.

If you have a multimeter with "Diode test" mode, connecting the leads across one of the LEDs in the correct direction should show a forward voltage reading, somewhere probably between 1V to 1.3V

At the same time, you should be able to see the IR output with an appropriate camera or sensor.

That should work on a bare LED, or probably also while in circuit.

 

[amateur_24]

Do I need a decent multimeter to be able to do this test? I tried this test on a led taken straight off the tape but I couldn't get a reading with the probes either way round. I have tried my meter on a regular led and it gives me a reading but doesn't light up the led.

Is the diode mode just garbage?

 

[rjenkinsgb]

It is possibly the meter. The next alternative is a 9V battery with a 1K resistor in series - that should put a safe current through an LED, though I'd not use that on one in circuit.