Over time I bought a few PLEM 50 Laser Meters from LIDL/Parkside. Most of them worked flawlessy.
The last unit, however, PLEM 50 D4, is problematic. I almost constantly get "Error 255" messages at almost any distance and conditions (I am apparently not alone, judging on feedback on this and similar devices). The error is related to a problem with the sensor (low signal or so) and is expected at long distances, or in bright light. But on my D4 this is happening practically always, even when previous units worked flawlessly.
I opened the device and found that it uses
the module on the left
for which there also a
datasheet.
The brass disc on the left is some kind of led, which pulses red when it measures. The black rod above the led is some kind of lightguide passing the light towards the unit on the right that contains some kind of light sensor, and the lens used for measurement.
In my unit, the lightguide is a piece of transparent plastic, see the picture on the right, kept in place with some hot glue.
Moving the lightguide with my finger helps making
some correct measurement, but the device remains flaky.
I tried moving the lightguide around a bit, or gluing it
in place, but nothing really helped.
So I replaced with some aluminum foil, bent to reflect light from the diode towards the rest of the unit. Some experimentation bending the foil made the error disappear and the unit provided always a measurement. I then used some kapton tape to keep the reflector in place and closed the unit.
I cannot tell whether the original was calibrated correctly,
because I didn't really get any good measurements.
However, a possible cause is that the "modified lightguide"
made of aliminum may create a longer path than the original.