IR Proximity sensor problem

Hi folks, I'm new to this 3d printing and after building and successfully printing several parts without much problem I seem to of hit my first one.

The proximity sensor seems to be under reading values all of a sudden, I can't seem to get it to read that magic 600 anymore its like its very weak.

It does show its max value with a bit of paper up against it but there is no way I'm getting that 600 value I need for calibration.

The G31 used to read G31 Z3.5 P597 now it's reading G31 Z3.5 P136.

I've double checked all the wiring and made sure the probe command is being read from the SD card, checked the voltages from the duet and at the sensor, I've also used the M558 P1 which worked but the value never really changed.

So the question is do these IR probes fail like this or should I be doing something else ?

Should say I'm on stock firmware 1.09 (2015-04-21)

Thanks for reading

The amount of IR Light hitting/reflecting into the sensor is too low when you have a low reading of P136.
I have the suggested white labels in each corner and upon the end stop so that the sensor gets enough reflected light.

Also check that the quick-set nozzles are correctly set height wise;
As it could be that the nozzles have dropped, so hit the bed first and the sensor is higher than it was.

My G31 setting is G31 Z1.70 P609 I would think that 3.5mm would a bit too high and having a lower value would be better.
I had similar problems getting the correct z-height when printing and I also found that the cooling block was upside down

*Update
My understanding how the process of getting the correct Z-height. Is that it driven down until the value reads 600 +- 20, it then slows and moves down the set z value giving the slight grab upon a piece of paper. If it's tight then lower 3.5 down by small amount; this will make it less tight.

Edited 2 time(s). Last edit at 03/06/2016 07:01AM by orictosh.

---

Supporting 3D Printers with Parts and Build services.
Printer: Ormerod 2 (528.4) Duel extruder set-up with Aluminium X-Rib, RRPro Firmware v1.11-ch (2016-04-08)

Also check that sensor still sits square to the surface, could be out of wack, hit by curl-ups

Erik

Thanks for the help guys, you were spot on Orictosh, I'd replaced the cooling block mount with a different design and slapped it on upside down, seemed the obvious way to install it
I even swapped it back afterwards to rule it out and obviously put the original on upside down too !

Oh well I'm up to the latest firmware and web interface now, thanks again guys !