a small note on Eotechs

bullets

Since I had a dodgy Eotech at home I got wondering what was going on with it.

For some reason every time there was a bit of vibration or id tap it, it
would switch itself off. This happened only when I had it set to Red Reticle.
When setting it to green reticle colour it was fine.

(I never took pics cos I was in work with only a camera phone that would not focus on the PCB board and wires correctly)
Could not find anything physically wrong with it when I opened it up but I was very alarmed at its internal construction. When you move the spring loaded battery contacts or adjust the L/R U/D adjustment screws as the internals move very fine wires with very fine solder joints are moved. Thus a lot of issues with these things I reckon are from wires breaking or the contacts wearing. I think an actual wire internally may have been broken on mine.

When putting mine back together and I had it reassembled the reticle
was not perfectly clear so I took it apart again to look at the issue,
upon trying to power it on not fully assembled I accidentally burned out the
LED! :mad:

Some people think (since some of the eotechs have stickers with Laser warnings on them) that there is a laser that projects onto the glass but this is not true. Its a bi-colour LED. ie its not a seperate LED for green and red. Its a single LED that emits green or red via a circut depending on the direction of the current flow.
(of course I am talking about cheap Airsoft scopes and not the real thing)

I noticed with 2 other Eotechs that when pressed the colour change button
to switch from red to green they powered down.

A buddy took some measurements from the tiny pcb board inside these type of scopes and made an interesting discovery.

The Red Reticle colour Drew more from the batteries and used up more power than the green reticle when in use.

BUT!!!! when pressing the button to change the reticle colour from Red to Green the green led caused a larger voltage drop across the Circuit than when changing from green to red. (see chart below)
http://www.oksolar.com/led/led_color_chart.htm

This led to an interesting discovery.
When using 2 Rechargeable Nimh AA batteries that were 1.2v per cell (2.4v in total) that may not have been 100% charged it ment that when I pressed the reticle colour change button from red to green the voltage drop was too much and the scope powered off.

Using normal non-rechargeable alkaline AA batteries that were 1.5v (3v in total) it was enough juice and the issue went away so I could switch from Red to Green without issue.

Things I've learned. using 1.5v batteries can be more reliable that using 1.2v rechargables for scopes like this. Maybe it will sort out other issues too.

Also dont start messing with the power button when half assembled you might see a puff of smoke from the LED and your scope die a nasty death.
(Not to worry though it was my sacrificial lamb I've 4 more at home)

~B

Leftyflip

I love when some actually investigates things properly.
Nice post Bullets!

richieffff

I had an Eotech 551 here and the had the same problem with the red reticule and always wondering what the hell was wrong.
Thanks Bullets for investigating for me

bullets

unfortunately for me I know feck all about electronics (despite being in the design dept of an IC manufacturing company :eek: ) but not afraid to poke about if I learn by my mistakes. (The scope sat on a shelf for 2 years with the problem so was not using it anyway and it finally satisfied my curiosity about what they looked like inside)

The real-steel versions of these scopes had issues with powering off that were caused by vibration or movement also for different reasons.
with a jolt their batteries sometimes lost connection with the contacts and powered the scopes off, they released an aftermarket kit to resolve this
issue by adding a buffer/cushion to the battery contact area. (Don't think this is an issue with airsoft scopes though)

Also these lads opened some up too:
(PCB board in simpler on these and lacking a light sensor thats on the models I have)
http://www.youtube.com/user/AirsoftGearMods#p/u/12/mnzWKCuxpHo

(Also the two springs that are featured on the youtube video that airsoftgearmods lads made are a pain in the hole! when trying
to re-assemble the base plate on the scope, not sure what they are needed for, as best as I can see they scope will work
perfectly fine without these.)
~B

facemelter

thanks !! really good info in here very well done !

Darth Phoenix

Nicely done mate. Cheers for putting it up.


DP