Powerbook 180 & Tunnel Vision

[JDW]

But would the spots have resulted from 5~20° (°F?) higher than your chosen bake temperature, or would the spots have results from a SECOND BAKE regardless of temperature?

Separately from that, i agree that having a turkey thermometer or similar in the oven during the bake is key, and that is how I advise all people who watch my iMac graphics card bake videos. Because without the ability to know for certain if the oven temperature is stable, you run the risk of over-heating the item, which in the case of the iMac graphics card, can result in bottom-side components desoldering and falling off.

But in the case of the graphics card for the iMacs, the heat is actually fixing some issue in the CPU chip itself (albeit not permanently) and not reballing the chip as some contend. But in the case of the LCD, I have heard the baking is merely forcing moisture out of the LCD. Even so, it's not clear if that is 100% correct. But if it is correct, then it makes sense that too low a temperature would not be enough to force out or evaporate the moisture, and too high a temperature would cause delamination of the panel layers and/or cause deterioration of the liquid crystal.

 

[Neo117]

That is a really good question that I unfortunately don't have an answer to. I was thinking that the spots may have been produced due to local hot spots which resulted in the non-uniform appearance. I know when I did the dry run of the baking operation that I used a digital temperature readout with four thermocouples, and I saw a significant difference in temperature between the four thermocouples (placed at different locations on the tray.) That was what motivated me to use the parchment paper to try and even out the temperatures. Note that every oven is different so this is just for my oven (pretty bad one to be honest.) A convection oven probably wouldn't have this problem. Air movement would probably even the temperatures out in a higher quality oven.

I know that thermal gradients can result in delamination in 3D printing layers (ABS) so I theorized that having hot spots close to 212F for a water based adhesive between LCD layers could result in delamination, but I have no proof of that. It is just a theory at this point as I don't know what type of adhesive was used between layers. Also, I suspect that there is no perfect temperature for baking. My guess is that there is an optimal combination of time and temperature for the baking operation. So for 191F the optimal baking time may be 5 hours, but for 200+F it may be much shorter or longer for a lower temperature. Unfortunately, without a lot of lcds to test, it is hard to know for sure.

It would be very interesting to hear about the results that people have had when performing a second baking operation.

 

[croissantking]

That is a really good question that I unfortunately don't have an answer to. I was thinking that the spots may have been produced due to local hot spots which resulted in the non-uniform appearance. I know when I did the dry run of the baking operation that I used a digital temperature readout with four thermocouples, and I saw a significant difference in temperature between the four thermocouples (placed at different locations on the tray.) That was what motivated me to use the parchment paper to try and even out the temperatures. Note that every oven is different so this is just for my oven (pretty bad one to be honest.) A convection oven probably wouldn't have this problem. Air movement would probably even the temperatures out in a higher quality oven.

I know that thermal gradients can result in delamination in 3D printing layers (ABS) so I theorized that having hot spots close to 212F for a water based adhesive between LCD layers could result in delamination, but I have no proof of that. It is just a theory at this point as I don't know what type of adhesive was used between layers. Also, I suspect that there is no perfect temperature for baking. My guess is that there is an optimal combination of time and temperature for the baking operation. So for 191F the optimal baking time may be 5 hours, but for 200+F it may be much shorter or longer for a lower temperature. Unfortunately, without a lot of lcds to test, it is hard to know for sure.

It would be very interesting to hear about the results that people have had when performing a second baking operation.

I successfully restored a PB180 LCD, which required two bakes, and it did not develop any dark spots.

 

[JDW]

I successfully restored a PB180 LCD, which required two bakes, and it did not develop any dark spots.

At what temperature for each bake, and were thermometers used to confirm those temperatures?