MK 137 IR checker

I’ve built more complex kits before this one but somehow I cannot seem to figure out what I did wrong.
Circuit board marked Vellman PMK137’1

Component placement checked multiple times.
Solder joints checked
fresh battery used
polarity of components checked.
solder points checked under magnifying glass to ensure no shorts.

I followed the instructions to the letter.

Unit doesn’t seem to work. When powered on all 5 red leds turn on and stay on.
No ir remote has any effect on the unit at all; at 5cm, touching the ir sensor… nothing.

I’ll assume I did something wrong but I’ll be darned if I can spot it.


Can you provide LINKS to HI-RES and SHARP pics of your assembly (both solder and component side) so that we can take a look?

Here are the images both sides

If it’s something really obvious I’m going to be disappointed in myself…


Compliments on the soldering job, one of the best we’ve ever seen.
Component placement looks OK as far as we can see.

Possible causes:

Transistors have been mixed up: Make sure BC547 and BC557 are not interchanged.

Defective transistor

Defective phototransistor.

Thanks for the compliments. My late father was a old school amateur ( HAM) radio man and all around electronics
wizard ( I remember as a young child watching him grinding the quartz plates from crystals on a glass plate to modify the frequency) so I had to at least learn proper soldering techniques or I’d have been drummed out of the house…

I confirmed the placement of the BC547 and BC557 components are as the schematic indicates. I don’t have the
means to test them nor the photo transistor.

I wouldn’t know where to obtain replacement components so I may have to scrap this and try to find another

Thanks for your advice.


If you provide an address I’d be happy to mail spare transistors and a phototransistor.

How do I send you my address?


We would like you to please send a mail to Mention the parts that you need (the more details, the better), and include your name and full address.

I have also an issue with my velleman IR remote checker kit (MK137) which does not work.
When I turn on the switch the LD5 turns on as expected but the other led’s don’t react if I point a remote at the sensor.

I already checked :
the resistors color codes
the polarity of the 5 led’s and the phototransistor
the correct placement of the transistors (BC557 (2) and BC547)
the battery which powers the circuit
the batteries powering different remotes I used
the soldering work looks ok (it is my 5th kit but the first which does not work)

What I didn’t check before soldering :
Measuring the real value of the résistors, capacitor.
If the transistors, phototransistor work correctly

I cannot figure out what I did wrong, please help.
Kind regards

Hi @adabull

Please post a picture of your kit.
Would be really helpfull.


1 Like

Are you holding the remote about 5cm from the MK137 as described in the manual?

1 Like

I tried from 0 to 20 cm and in various angles.


Can you find any error ?

Hi everything looks OK except some soldering points. they can be OK but please double check and reheat them

second attempt successful