How to fix: Casio PRG-90T-7V Titanium Protrek Series “op en” error



The Casio Protrek is a popular line of outdoor watches that are known for their durability and accuracy. However, some Protrek watches can sometimes display the error message “OP EN” or “OPEN”. This error message usually means that the watch’s battery is low or that the watch is not properly sealed.

Causes of the Error:

There are a few possible causes of the “OP EN” or “OPEN” error on a Casio Protrek watch. These include:

A low battery: If the watch’s battery is low, it may not be able to power the display properly. This can cause the watch to display the “OP EN” or “OPEN” error message.
A loose seal: The watch may also be displaying the error message if the seal around the case is loose. This can allow moisture to get inside the watch, which can damage the electronics.
A faulty sensor: In some cases, the error message may be caused by a faulty sensor. This can happen if the sensor is damaged or if it is not properly calibrated.

How to Fix the Error:

The first step to fixing the “OP EN” or “OPEN” error on a Casio Protrek watch is to check the battery. If the battery is low, you will need to replace it. You can usually find replacement batteries at most electronics stores.

Once you have replaced the battery, you should check the seal around the case. If the seal is loose, you will need to tighten it. You can do this by using a small screwdriver to tighten the screws that hold the case together.

If the seal is not loose and the battery is not low, then the error message may be caused by a faulty sensor. In this case, you will need to take the watch to a Casio authorized service center for repairs or see below for self repair.


The “OP EN” or “OPEN” error on a Casio Protrek watch can be caused by a number of factors. However, the most common causes are a low battery or a loose seal. If you are experiencing this error, you can usually fix it by replacing the battery or tightening the seal. However, if the error persists, you will need to take the watch to a Casio authorized service center for repairs.


To prevent the “OP EN” or “OPEN” error from happening, you should always keep the battery in your Protrek watch fully charged.
You should also inspect the seal around the case regularly to make sure that it is not loose.
If you are going to be using your Protrek watch in wet or humid conditions, you should apply a layer of water resistance grease to the seal.

Self Repair:

I’ve had this watch for about 3 years. A few days back I found that my Casio Protrek Triple Sensor PRG-90T-7V displaying “op en” instead of the date. Casio PRG-90T-7V Titanium Protrek Series op en errorNone of the buttons are working, only the Auto EL feature is working.

Here is what I do to fix it:

The PRG-90T-7V (probably all the Casio PRG series) has a couple of little springs inside that make contact with the back plate. If those springs are missing, then the watch thinks that the back plate is missing. It also display the same error if the backplate removed.

*** I am sorry for the quality of the pictures here, they all taken with my cellphone. I have no camera ready at the time of this work. ***

Here is the picture of my PRG-90T-7V showing “op en”.

PRG-90T-7V showing "op en"
PRG-90T-7V showing “op en”

I do not recommend that you try to fix it yourself. You should send it to Casio for a service. I do this because there is no Casio service center in my area and sending it to another nearest service center will take days.

[*] Find a small (+) screw driver before you begin.

[*] Remove the band. You have to do this before you can get the backplate off. Be careful with the claps that holding the band. This can be difficult because you need to disengaged two spring bars simultaneusly. Be patients and slow, the spring bars tend to fly when you remove the clasp. Do not lose the them.

[*] Unscrew the sensor part. See the picture below.

Unscrew the sensor part
Unscrew the sensor part

There is two screws there.

There is two screws
There is two screws

[*] Then you need to remove the plastic/resin that obstructing you from getting the back off.

remove the plastic/resin
remove the plastic/resin

You need to pull them carefully especially the one near the sensor. I cannot get this one off, because there is some part of it that stuck under black part which has “TOUGH SOLAR” text.
Here is how to pull them off. Be gently. Follow the yellow arrow to pull them.

Follow the yellow arrow
Follow the yellow arrow


Follow the yellow arrow
Follow the yellow arrow

Here is how it looks after pulled off, notice the one that still there — the part marked with blue [A]. While the other one [B] is pulled off. There are 4 screws there (blue circles), unscrew them off gently. Push the backplate with your finger while unscrewing to prevent the springs inside flying off while you pull the backplate off.

There are 4 screws
There are 4 screws

[*] Here is the backplate after pulled off.

the backplate
the backplate

[*] Here is the watch without the backplate.

the watch without the backplate
the watch without the backplate

There are 3 springs there, red circles. The two which close to each other is the backplate detector.
The black rubber ring showing by the blue arrows is the seal that helps makes the watch water resistant.

[*] This is the inside of the backplate.

inside of the backplate
inside of the backplate

There is a small plate (yellow circle) glued to the backplate which is not where it should be. The heat here in my city probably the cause of it moves. I had to push the small plate upward as shows by the arrow. Once it back to the right position, test it by putting the backplate back (without screwing) to see the watch if “op en” error dissapear. If not, move the small plate where you think the right position is. It should be on top of the two springs which close to each other.

[*] If the error dissapear, put back the backplate, screw in. Put back the plastic/resin carefully. Screw the sensor part. Lastly, put back the band.

[*] Here is the picture of the watch after fixed. The date is back, YAY!

after fixed
after fixed

Good luck!


  • Daniel September 18, 2015 Reply

    Thank you very much, your “how to” helped me fixing my Protrek!

  • Rodrigo Valdez December 14, 2016 Reply

    Thank you very much, it was very useful, it helped me recover my watch.

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