Background of issue: I have a LED lamp with 2 different modes and an on/off switch for each of these. There is a fan that's supposed to be cooling off the LEDs but is not functioning in 1 of the modes, so after taking the thing apart I found a small circuit board (illustrated in the attachment).

I have very limited knowledge in electronics but it's obvious the fan won't work for switch 1 since the wires are isolated and only the 2nd switch is connected to the fan wires through a bridge rectifier(MB10S).

Seems to me that the board was either set up wrong to start with or it's just wired incorrectly, and I'm trying to understand what's going on here.

What purpose does the bridge rectifier serve in this case ? Would it be an issue if I wired Switch1 directly to the fan wires ? Or is there a better way to make this work ?

**I have no idea what the L and N stand for, that's just how the board is labeled on the back.

enter image description here

  • \$\begingroup\$ Is there any bottom trace running out.I find ,there is grey wire.What is that? \$\endgroup\$
    – Aadarsh
    Commented Jan 10, 2016 at 6:32
  • \$\begingroup\$ what is the function of switch #1 and switch #2 on the lamp? it seems that wiring them together would defeat the need for two switches it also seems that switch #2 is the on/off switch and switch #1 is a mode selector switch there may be mis-wiring in another part of the lamp \$\endgroup\$
    – user96635
    Commented Jan 10, 2016 at 7:12
  • \$\begingroup\$ If the mode where the fan does not operate is a lower-power mode then it is possible that the fan cooling is not required in that mode. Could that be the case? \$\endgroup\$ Commented Jan 10, 2016 at 9:29
  • \$\begingroup\$ I think switch 1 and switch 2 are the 2 wires going to the switch. There is only 1 switch. The PCB layout is correct then. This board will make DC at the full mains voltage, so be careful, both + and - will be at dangerous potentials. \$\endgroup\$ Commented Jan 10, 2016 at 13:02

1 Answer 1


Please forget about the switch 1.It's not connected anywhere.Come to the point of switch 2.The L and N stands for Line and Neural in the AC power supply,which you get in your home.Current flow from Line to Neutral.The MB10S,as you said is a bridge rectifier.

    A bridge rectifier will convert an AC current to pulsating DC current.In AC current we use Line and Neutral,in DC current,as you know,we represent +ve and -ve terminals.
    Your output to the fan may be a DC motor,so you use a AC to DC converter like the bridge rectifier.But actually,this circuit is supposed to work.Make sure that the AC input given voltage limited(below the maximum voltage that bridge rectifier can tolerate and work fine).Otherwise,the rectifier will burn or damage.
    You can find the line and neutral by using a tester.If you put the tester in Line,The LED inside will glow.If it's neutral,the LED wont glow.
    In your PCB,add a capacitor in-between the +ve and -Ve output parallel to the output to stablise the DC current and so that you can get almost a good DC voltage.The capacitor will eliminate the ripples from the rectifier(the smoothing of pulsating DC voltage) and you'll get a better DC current.The more capacitance you add,that much ripples are eliminated.
    Use a step down transformer to the L and N point of the PCB like 9-0-9 V transformer or 12-0-12 V.I don't find anything wrong with this circuit.
    If you think to control also by switch 1 solder the switch 1's L to switch 2 L.Also for the N wire also.Here is the picture

  • \$\begingroup\$ Hey Aadarsh, thank you for the answer. There is nothing wrong with this circuit other than the fact that it doesn't work as intended. Switch 2 will turn on the fan with no issues, but as you can't see there's no way for the Switch 1 to do the same with the current setup. \$\endgroup\$ Commented Jan 10, 2016 at 6:38
  • \$\begingroup\$ You can make a connection between the swtich 1 and MB10S.Take a wire and solder one side L in swtich 1 and solder it to the swtich 2 L. In the same way,do it for swtich 1 and switch 2 .That's it \$\endgroup\$
    – Aadarsh
    Commented Jan 10, 2016 at 6:40
  • \$\begingroup\$ Thank you, will give that a try. Any idea what went wrong here ? It's an expensive piece of equipment I'm working on and the fan being on in both modes is a vital part of its functionality, so I hardly doubt they wired Switch 1 not to work on purpose, they could've just not have wires at all. Was the board printed wrong ? Did they wired it wrong ? \$\endgroup\$ Commented Jan 10, 2016 at 6:44
  • \$\begingroup\$ They may forget to route from switch 1 to switch 2.Moreover,it's mistake only.Make sure that you use any one switch to turn ON the circuit.Not a issue if two are ON,since the connection is in parallel.But current flow may increase.Still not an issue. :p \$\endgroup\$
    – Aadarsh
    Commented Jan 10, 2016 at 6:48
  • \$\begingroup\$ Dont worry about,wrongly routed PCB or un-routed trace in PCB.There are some tricks which you can do using soldering.If you want to cut a route,just rub the routed part with a sandpaper until you cant see any copper connection left.If you want to join,just use a external wire,so that you can get a route \$\endgroup\$
    – Aadarsh
    Commented Jan 10, 2016 at 6:51

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