I just changed both polarizers on a THS720 I got off eBay for relatively cheap. I used one of these heated scrapers off eBay to help separate the polarizers from the glass:
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F322448570325The adhesive is tenacious, and pretty thick. It took awhile to remove them. Then the adhesive residue was quite heavy. I used a bunch of single edged razor blades to get the remaining residue off the glass. When it was about 99% removed, I used acetone to remove what little was left. If you try to use acetone on the thick residue, it just smears it around, so scrape off the vast majority.
I bought these polarizer sheets off eBay:
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F263269289709Putting these on it a lot like putting a screen protector on a cellphone; one bit of dust causes a bubble. Fortunately, the adhesive allows them to peel off cleanly. I ended up using 4 of the 5 sheets I got, and I cut two polarizers per sheet.
If the front polarizer is one way, you get white on a black background. Turn it 90 degrees, and you get black on white. Between dust and getting the front sheet polarity wrong caused me to use up so many sheets.
The LCD is super easy to remove. 4 screws in the back corners allows the front of the scope case to come off. Fold down the front metal touchpad plate, and the LCD is exposed. There are no screws holding it in place, just some rubber pads. With the scope face up and in the normal position, simply lift the LCD from the right and fold it to the left. Disconnect the zif ribbon cable from the back, and the connector for the backlight cable. Once you have the LCD out, turn it over, and bend back the small tabs holding it together, and the front and back of the metal case can separate. You should NOT remove the two small screws. They simply hold the plastic cover for the backlight, and don't keep the display from being disassembled. I laid the lcd panel on some microfiber cloths on a flat surface to remove the polarizers. The glass is pretty thin, so you need to be careful not to break it.
When reassembling, make sure that the glass is absolutely flat and not cocked in the metal frame, or it could crack. Note that there are some silicon strips between the glass and front frame on two sides, the sides away from the circuit boards. They keep the glass from touching the frame.
The new polarizer sheets are slightly thicker than the old, but work great. Note that there are plastic protective sheets on both sides of the new polarizer that need to be removed, one over the adhesive. Don't remove the other sheet until both polarizers are installed, and all bubbles are out between the polarizers and glass.
My scope was barely legible even in the dark, and then only portions were readable. It looked a lot like the one in this thread. After replacement of the polarizers, it's like new. A great way to save $175.
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