Replace or repair old LCD screen

[R_C]

I would like to save the control head on my boat's 20-year old auto pilot. The control head still works but the LCD screens are now mostly unreadable. There are no part numbers on the two LCDs you can see in the images. I untwisted the tabs that hold the smaller LCD in place and flipped it upside down in the second image. There is just a rubber strip that makes contacts with the pads on the board. Is there any way to disassemble the LCD itself? Any thoughts or suggestions are appreciated. Thanks.

 

[KeepItSimpleStupid]

The rubber strip is usually a conductive elastomer that has alternating areas of conduction.

I ONCE disassembled a watch and replaced the polarizer.

Try to figure out what's driving the thing and the numbe rof pins and whether a backlight was used.

Strangely enough, this URLhttp://www.lcdrepair.eu/ showed up in a search.

 

[ronsimpson]

I don't think you could get a replacement when the unite was new. Now you really can't find a replacement.

 

[R_C]

It appeared a leaky capacitor had spilled into both LCDs. I disassembled the small one by separating the plastic backlight, then the two pieces of glass and cleaned the oily residue but that didn't work. Could the oil have come from the capacitor or is that the "liquid" in LCD?

 

[Nigel Goodwin]

It appeared a leaky capacitor had spilled into both LCDs. I disassembled the small one by separating the plastic backlight, then the two pieces of glass and cleaned the oily residue but that didn't work. Could the oil have come from the capacitor or is that the "liquid" in LCD?

Probably the 'liquid' (nematic crystals), and you've certainly destroyed it by ripping the glass apart.

The fault is probably the rubber strips, they do tend to fail over time, and are often a nightmare to put back once you disturb them.

 

[R_C]

There was no ripping apart. Just a small dab of what looked like hot glue held only one side of the two glass strips together. I don't understand how any fluid could have been held between the two pieces. I thought any fluid would be held within a sealed unit.

When I separated the LCD from the board, one of the rubber strips remained with the board while the other remained fastened to the glass. Maybe that's the problem.

 

[Nigel Goodwin]

There was no ripping apart. Just a small dab of what looked like hot glue held only one side of the two glass strips together. I don't understand how any fluid could have been held between the two pieces.

It's not any more

Time to buy a new auto-pilot I think.

 

[picbits]

or keep an eye open on Ebay for one with a different fault and swap the modules over.

 

[R_C]

I bought this unit cheaply on eBay just for parts but hoped I could revive the LCDs. I still have a working control head. Unfortunately, units only rarely appear on eBay.

 

[R_C]

Would it be possible to reverse engineer how the board drives its LCD then create a new interface to an external LCD by monitoring the signals on the board's LCD pads? I know this may be a stretch, but it could be a cool learning project. The board has 56 pads top and bottom for the LCD with a pitch of 1.25mm between pads so it wouldn't be impossible to solder some ribbon cable to the pads.

 

[Nigel Goodwin]

It would certainly be 'possible', but not particularly easy - it doesn't help that the drive is AC, and almost certainly multiplexed.

It would certainly be a 'cool' learning project though.

 

[R_C]

Still thinking about a solution to revive at least the smaller of the two LCDs, which would be helpful if my working unit's LCD fails. I determined this 80 columns by 28 rows LCD uses one PCF8578T driver and two PCF8579 40-column LCD drivers. The PCF8578T datasheet shows it uses an I2C interface and documents the I2C commands. After deciphering the I2C commands, could a separate microcontroller read this board's I2C commands and draw on its own LCD?

 

[Nigel Goodwin]

Still thinking about a solution to revive at least the smaller of the two LCDs, which would be helpful if my working unit's LCD fails. I determined this 80 columns by 28 rows LCD uses one PCF8578T driver and two PCF8579 40-column LCD drivers. The PCF8578T datasheet shows it uses an I2C interface and documents the I2C commands. After deciphering the I2C commands, could a separate microcontroller read this board's I2C commands and draw on its own LCD?

Of course it could, it's 'just' a question of reverse engineering it all - but at least you have the documentation for the driver chips which would make it a LOT easier.

 

[claudinemann25]

Sometimes repairing can cost almost the same as buying a new one. If repairing or replacement exceeds its original amount, then it is a waste of time keeping it. Buy a new one instead as this has more value and warranty.