View Full Version : Board sensor reads 0

Rob Mulgrew
10-09-2015, 01:26 PM
After putting in a new board sensor recently I have been getting low readings and eventually it went to a “0” reading and wouldn’t work at all. I took out the board sensor and the lens wasn’t dirty but I heard a little plastic piece fall when I took the board sensor out. I believe it was a little transistor but I’m not sure of the correct name for it. It was so small (about 1/8 of inch in size) I couldn’t solder the 3 points back to the circuit board so I tried something I seen on Youtube to bypass the missing piece I just put a blob of solder over all 3 contact points on the circuit board and put it back inand it works just fine again.
My question is,
is there any danger to running the machine like this and can this cause any other issues?

10-09-2015, 02:11 PM
I don't recommend putting solder over the 3 contacts. Normally the transistors act as a switch. It will have a positive voltage on one contact and another going to a load of something they want to turn on. The 3rd contact is sort of the gate to turn on the switch. If you short them together then bad things can happen.

Most of the parts have a white silk screened rectangle around the parts so you can see if one is missing.

Since the part fell off you could post very clear pictures here of the part and the board with the missing part then call LHR... Being a Friday better call fast...


10-09-2015, 02:28 PM
Yes, lets see a picture of that!

Rob Mulgrew
10-09-2015, 02:57 PM

Bottom left is where the solder was applied. As for the piece that was there I accidently blew it somewhere off the table with the air hose and it will most likely never be found again.
My thought was on this that I was already going to have to buy a new board sensor so what do I got to lose. And then after I put it in and it worked perfectly I started wondering why that piece was there in the first place and was starting to get nervous that I can damage something else in the machine.

10-09-2015, 03:06 PM
Notice C6 has also been scraped off of the board. A miracle that it works. Thanks for the picture. I have some old sensors I will now play with.

Rob Mulgrew
10-09-2015, 03:15 PM
I didn't even realize that C6 was gone too. Honestly nothing touched any pieces on the circuit board when installing this. I'm not sure why the pieces would fall off or where the other one (c6) went for that matter. I've taken out and put in the board sensor at least 50 times. Since day one board sensors have been an issue on my machine, usually just dust behind the lens though.

10-09-2015, 03:20 PM
The C6 comes off easily because the plug scrapes it off. I have two like that. One has to make sure the plug gets pulled away from the board as it comes out.

Rob Mulgrew
10-09-2015, 03:35 PM
Would it make sense to have an option to not even use the board sensor? I can measure my work piece accurately and tell the machine where the center of the project is. I'm really just thinking out loud. Is that something that has ever been discussed around here and is it a bad idea?

10-09-2015, 06:50 PM
Just guessing, I would bet that the transistor just turns on the IR LED's and now they are on all the time. A Camera with IR Mode could tell.... Never looked at my board sensor to see if it was off until needed. Curious what the board sensor reading is with white paper now?

As for the need... Finding the board edges, all 4 is a important function.

Good Job


Rob Mulgrew
10-11-2015, 06:53 PM
Hey Al,
I checked the board sensor reading with white paper and it now reads at 77. I realize that's quite low and I'm going to order a new board sensor but at least its good to know you can run it like this when in a jam if necessary.

10-11-2015, 06:58 PM
With nothing to loose... I would take a knife and cut down the back of the black plastic removing the flap. That will expose the LED's and Photo detector and let you slide the window out and clean it. Seal is all back up with tape...

And I would order a 4 wire board sensor cable too... It will let you test them from the top of the machine. See part number on the 2011 parts order... the last time I ordered parts...


Rob Mulgrew
10-12-2015, 07:05 PM
Great idea on ordering another wire, I'll definitely look into that.
As for cleaning the lens, I do take them out and clean them but noticed they get scuffed and scraped over time so I kept an old plastic package from some tool I bought a while back and a couple times a year I cut a new lens's and put it in.
Thanks for all the recommendations