Brother HL-5140 laser printer - drum signal light flashing on and off at 2-3 sec intervals. What do I need to do?

1. Turn the printer off.
2. Press and hold the Go button on the front of the printer, at the same time turn the printer power on.
3. When the Toner light is on by itself, release the Go button.
4. Push and hold the Go button again, release the Go button when the Paper light is on by itself.

This should reset the DRUM counter.

With the front cover open, press and hold down Go button until all 4 LEDs are lit. Once all 4 LEDs are lit, release the go button, then close the front cover.

This will reset the drum counter.

the drum is the tray that holds the toner, it comes out when you remove the toner. you can buy this part at any store that sells the toners. it is normally more expensive than the toner but will last you about 4 of them

The drum light flashes when the drum is almost used up and solid when it is used up. You open the front door and hold the go button til all lights flash and that resets the drum counter. You may need also to run the blue tab on top of the drum back and forth about 20 times to clean the corona...

DRUM UNIT "spent"
It can be reset if the printing quality is good
To reset the drum follow the instructions below:
Press the cover release button and then open the front cover of the printer.

Press and hold down Go button until all 4 LEDs are lit. Once all 4 LEDs are lit, release the Go button.

Close the front cover.
Make sure that the Drum LED is now off.
Caution: Reset the drum counter only when you replaced the drum unit with a new one.

change the drum , the problem coming from drum.

I have reused the drum for three life cycles and the print quality is still good. Just reset the counter until the print quality suffers because the cost of the drum exceeds the price of a new printer. According to Brother to reset the counter

1. Turn the printer off.
2. Press and hold the Go button on the front of the printer, at the same time turn the printer power on.
3. When the Toner light is on by itself, release the Go button.
4. Push and hold the Go button again, release the Go button when the Paper light is on by itself.

its the sensor, its not aligned to specs. make sure the drum is in its proper space then, unplug for 5 min to reset the control panel.

There isn't a cleaning page on a Brother 5140. If the smudges are about 3.5 inches give or take a little and the same each time in a line it's probably the drum is damaged. If they are closer like 1-3/8" to 1-1/2" it will likely be the toner cartridge.

If it spaces out a more, something like 2-1/2 it will be the fuser.

Sounds more like toner cartridge though.

Hope that helps you.

make sure you have the drum seated all the way in, then unplug the printer and plug it back in.