Red error light continuously blinking - Samsung ML-2851ND Laser Printer

1. If both round and long LED's are blinking, unplug the opener motor for five seconds, and replug. If the lights go back to normal, it was just a program error. If they both continue to blink, it's probably not user-serviceable.
2. If the round LED is blinking and the long LED is off, it is usually the door sensors that are obstructed or knocked out of line.
3. If the Long LED is blinking and the round LED is off, it is usually a bad roller or hinge that won't let the door move freely, something stuck in a track or a bent track.

These blinks [flashes] are fault indication (Error Codes). From the number of blinks occur at one time switch ON, you can get an idea about the faulty circuit section inside it. This will make repair easy. These are called blinking codes. Make sure about the exact number of blinking of the standby/power LED, by switching On & OFF the set, for at least two times. Count it carefully. If you wish to get some details, check the site linked here. It has details about blinking codes, and fault locating procedure, to many popular brand TVs and other devices. http://electronicshelponline.blogspot.com/
Blinking codes details to many popular brand TVs are given. Surf the site with patience. If blinks continue without any pause, the main board is faulty.

Six blinks - No Horizontal (H STOP), no raster, goes to the blinking self-diagnosis function immediately. Check C515 & 516 and the jungle IC, IC206. To get more details, http://electronicshelponline.blogspot.com/

thats usually an error code. How many times does the light blink?

It cannot be reset fully unless it comes on and stays on (the model you have listed here.)

That set should have a blink error code--watch the red power light to see if blinking in a number sequence like 7blinks pause and repeats over and over.

I will need the model number of your sont because different model numbers have different diagnosis codes.

Hi,
4 times red standby light indicates problem with exhaust fan that is not running for some reason.
Recheck fan that you replaced and make sure its connector is plugged properly and it running freely.
4 times red light blinking is fan error in this tv.
Thanks.

both light are blinking at the same time or blinking alternatively ?
if both blinking same time, it's a fatal error.. means it could be something wrong with the carriage or board or encoder belt...
if the light blink alternatively, it means the waste ink counter need to be reset and ink pad need to be replaced.

Those blinks [flashes] are fault indication (Error Codes). From the number of blinks occur at one time switch ON, you can get an idea about the faulty circuit section inside it. This will make repair easy. These are called blinking codes. Make sure about the exact number of blinking of the standby/power LED, by switching On & OFF the set, for at least two times. Count it carefully. If you wish to get some details, check the site linked here. It has details about blinking codes, and fault locating procedure, to many popular brand TVs and other devices.
http://electro-medical.blogspot.com/
http://homenol.blogspot.com/
http://electronicshelponline.blogspot.com/
If blinks continue without any pause, the main board is faulty.