Thank you so much. You have a been a great help and this has been a nice lesson for me. If I find a display should I post it here or start a new thread?

I looked at another site and found the same lcd you mentioned at the top of this post. It's out of stock so I emailed them to see if there is a replacement part.

I would suggest posting in this thread. I appreciate continuity and knowing how things work out, good or bad.

BTW, this is the book I use for my logs. It looks nice, is durable, but a little more expensive than some: https://www.amazon.com/Boorum-Pease-96304-Record-Account/dp/B0013CFWBQ You may find it cheaper elsewhere. It's also been quite a few years since I bought them.

Edit: Mine are made in the USA. They are that old.

 

Thank you for the suggestion. I sure wish there would have been a sure fire solution to this display thing but that's the way it goes sometimes. I'm not sure how long it will take but I'll follow up with whatever I end up doing, or with a display if I find one. Thanks for everything.

 

I've been testing pins. I can get a small flicker from time to time, but it's in bad enough condition that segment will not stay lit.
From left to right, I can get a segment to light up when I have a lead on pin 1, and the other on lead 7, 8 or 11. There might be others that should work but they just aren't showing up because of the condition.
That was actually kind of a fun little test. I'm not sure what it tells me though.

One last thought.
I wonder if the melted plastic stuff is what's left of one or both polarizers. If either is defective, the LCD won't show the segments even if the glass is good. You could get some polarizing film (linear polarization) to replace one or both. To test the idea, peel the worst side off, energize the display as before and look at through polarized sunglasses. If you see well formed segments, you are there.

I searched around and there are outfits that rebuild JD dashboards for a fixed price. No idea how they do.
Sorry to be a pest. I hate the loss of repair rights, too.

Good luck!

 

I just looked and sure enough, there is a thin piece of film on that white backing. The other side of the glad has the film still in tact and it looks good. Do you think replacing the polarizing film on the back will fix this?

 

I got excited and forgot what you said about testing it with polarized glasses. I'll do that tomorrow. I'll update afterwards.

 

I just looked and sure enough, there is a thin piece of film on that white backing. The other side of the glad has the film still in tact and it looks good. Do you think replacing the polarizing film on the back will fix this?

Possibly.. The display is a glass sandwich with a polarizer on the front and back stuck to the glass. For an unlit display, there is also a reflective sticker on the back behind the back polarizer. The polarizers are oriented so that their ‘grain’ is 90 degrees to each other for dark segments on a light background. Usually a bad glass will have some physical damage or internal plating from a bad driver which looks a segment stuck on all the time.

The glue that sticks the polarizers on is pretty strong. I use alcohol and a flat bladed x-acto knife to gently scrape the glass clean.

https://www.pacificdisplay.com/lcd_oper_basics.htm

This from Wikipedia is what you are looking to do with new polarizers. The front one is removed from the glass. The segments are revealed when looking through an external polarizer. The segments are light on dark because the polarizer is rotated. If it were rotated 90deg, it would show the segments dark on a light background. The shiny reflector is visible where the front polarizer isn’t over the glass.

https://en.wikipedia.org/wiki/Liquid-crystal_display

Good luck!

 

I was going to ask, how do you know that the LCD is bad?

As JohnInTx suggests, use your DMM to identify the pin connections on the LCD module. Then try the polarizer for viewing.

 

I'm back at it. The adhesive came off easily with alcohol, no scraping. I'm certain all that was on the glass was adhesive and the polarizing film has been melted onto the reflector (term?). So, I tapped some pins with my multimeter and, using polarizing glasses, I was able to see segments light up more, and more often, than I was able to yesterday.

When the segments light up, they only stay on for a split second then fade away. I've looked at some videos and have only seen people testing 7 segment lcds. When they test them the segments stay on however long they have the multimeter leads on the pins. Is the glass I have different? Or is it possible my multimeter?

 

Thanks MrChips. As you may have guessed, my knowledge in this field is limited. After learning more about how lcds work, I now understand that something as simple as the polarizing film could be the problem. With that being said, I'm far from being an expert in this area. I've identified that the film on one side is indeed bad, however, I'm still having trouble identifying the pins. Whenever I attach the leads from my DMM, I can see segments become active but they fade away very quickly. I'm trying to understand why this is happening and if there is a solution. Again, I'm grateful for any input and I'm enjoying learning about this.

 

Just for grins I googled

polarizing film for lcd screen

and got lots of hits including
http://www.lcdparts.net/Film3D.aspx

and Amazon
https://www.amazon.com/Polarizing-F...eywords=polarizing+film&qid=1599498278&sr=8-3

A couple of the reviews on Amazon show replacing polarizers on various tractor, ATV panels so you're not the only one. It's unclear if all of them have adhesive or just use static cling.

Fun!

 

Thanks MrChips. As you may have guessed, my knowledge in this field is limited. After learning more about how lcds work, I now understand that something as simple as the polarizing film could be the problem. With that being said, I'm far from being an expert in this area. I've identified that the film on one side is indeed bad, however, I'm still having trouble identifying the pins. Whenever I attach the leads from my DMM, I can see segments become active but they fade away very quickly. I'm trying to understand why this is happening and if there is a solution. Again, I'm grateful for any input and I'm enjoying learning about this.

Not to worry. We are all learning from each other.

LCD need AC voltage to turn on the segments. I don't know if that is the reason why you see them fade away quickly. I am looking to see if I have some spare LCD in order for me to test.

In any case, I am betting on your problem being bad polarizers. Follow JohnInTX's lead and see if replacing the polarizer will get it working.

 

Yes, I found some I would feel comfortable offering for about $10. It had the adhesive on it. I was hoping to get some thoughts from you all about why the segments are fading away when I have my DMM leads on the pins. Is that normal behavior for a display like this? If that is normal, then I'll order the film and move forward.

 

I literally clicked 'submit' on my last post as your post was coming through. Thanks for your input. I'll get the film, give it a shot, and report back.

 

Have you tried installing the LCD back in the holes but without soldering. The leads are probably stiff enough that angling it to one side with a little pressure may give good enough contact to see the numbers, if any.

 

Have you tried installing the LCD back in the holes but without soldering. The leads are probably stiff enough that angling it to one side with a little pressure may give good enough contact to see the numbers, if any.

That's a great idea! I'll try that first to see what happens. Might take me a little bit to tear it down again and get it ready for testing.

 

I put the lcd in the board, unsoldered, and turned it on. Using polarized glasses, I was able to see a fee digits, which is more than I have ever been able to see. It looks like the bottom segment of one is missing but with the way I was having to look at it, and it being unsoldered, it's possible it works, or was working, and I just couldn't see it. I've ordered polarizing film so I will update after I install it.

My next obstacle is soldering it back onto the board. I have some experience soldering but these pins are small and closer together than I'm used to. I am going to buy a finer tip for my soldering iron to see if that helps with accuracy. Even if this turns out less than perfect, if I can read the hours on this display I will consider it a success.

I know I keep saying Thank You, but I just can't say it enough. You all have been incredible.

 

Before you re-solder it, get some "solder wick." I prefer Chemtronics brand as do a lot of others. Sizes 2 or 3 is about all I ever use. Size 3 is a little wider. Size 2 works better with smaller stuff, which is what I use most by far. It will last you a long time, the the minimal length (3 m) is what I recommend.

Then, clean up the pads from which you unsoldered the display. Pay particular attention to splashes and shorts (There is one potential short in your original post.) My preference would be to repair the polarizer and reflector before reassembling. After doing all that carefully, and if it still doesn't work, you may just want to leave it be. If you do decide to remove it again, cutting the leads and unsoldering each one separately is the safest. We often see people who are relatively new to soldering pulling a pad away from the PCB. That can be difficult to repair.

 

Before you re-solder it, get some "solder wick." I prefer Chemtronics brand as do a lot of others. Sizes 2 or 3 is about all I ever use. Size 3 is a little wider. Size 2 works better with smaller stuff, which is what I use most by far. It will last you a long time, the the minimal length (3 m) is what I recommend.

Then, clean up the pads from which you unsoldered the display. Pay particular attention to splashes and shorts (There is one potential short in your original post.) My preference would be to repair the polarizer and reflector before reassembling. After doing all that carefully, and if it still doesn't work, you may just want to leave it be. If you do decide to remove it again, cutting the leads and unsoldering each one separately is the safest. We often see people who are relatively new to soldering pulling a pad away from the PCB. That can be difficult to repair.

Solder wick! I forgot about that stuff. I haven't used that in a long time. I'll pick some up, great advice.

 

One other thing. I'm not familiar with reflectors on lcds. When I search for this on the web I see several different types. Can anyone say what type would be applicable for my situation?

 

There are 3 types of LCD: transmissive that rely on a backlight, reflective that rely on reflection of ambient light, and transflective that allows it to be seen by either or both: https://caltronind.com/articles/transmissive-transflective-reflective-lcd-displays

Since yours does not have a backlight it is reflective or transflective. That's why it needs a mirror surface.

LCD elements, be they pixels or bars, cannot be seen without light. LED's can be seen without additional light.