LCD, functional but missing information - Page 1
Forum section: electronics / repair

author: viktor18
author_rank: Regular Contributor
timestamp: June 13, 2017, 09:39:01 am
content: Let me introduce this project by posting pictures of the problematic LCD and a functional one:These two displays are not entirely the same but serve the same purpose.Here's two other pictures of PCB's that drives this LCD:Any ideas of what might cause the problem and/or instructions on how to troubleshoot it?

author: viktor18
author_rank: Regular Contributor
timestamp: June 13, 2017, 12:37:44 pm
content: Update, the circled capacitors are missing electricity! On the healthy board they are getting a steady 24volt, but on the problematic board it's 0.. Hmm, need to figure out why.. The board is sprayed in some type of lacquer so makes poking around a pain in the ass.

author: bktemp
author_rank: Super Contributor
timestamp: June 13, 2017, 12:48:11 pm
content: I can see two problems:The missing columns in the middle of the screen are probably due to the damages tracks between T6A39 and the LCD in the last picture.The missing columns across the whole screen could be the T6963 running in 6bit instead of 8bit mode.

author: viktor18
author_rank: Regular Contributor
timestamp: June 13, 2017, 12:55:22 pm
content: Quote from: bktemp on June 13, 2017, 12:48:11 pmYou don't think it could be because 8 electrolytic capacitors are missing power?

author: bktemp
author_rank: Super Contributor
timestamp: June 13, 2017, 01:12:18 pm
content: The capacitors could be an additional problem.If you look at the screen, you can see the missing columns have a slightly different colour than all other inactive pixels. That tells me those columns in the middle get no signal at all. Since the T6A39 can not disable only a part of its output drives there must be some other problem. And since the damaged tracks are clearly visible, they are most likely the cause for the missing columns.Since the image is otherwise displayed correctly without any artefacts like crosstalk or low contrast, the analogue voltage on the LCD should be fine.The 6/8bit mode is controlled by the FS1 pin. This could be pin 1 of the connector. Verfiy if it is connected correctly (should be low for 8bit mode).

author: Samogon
author_rank: Frequent Contributor
timestamp: June 13, 2017, 01:17:49 pm
content: I would check zebra connector alignment.

author: viktor18
author_rank: Regular Contributor
timestamp: June 13, 2017, 01:31:06 pm
content: Quote from: bktemp on June 13, 2017, 01:12:18 pmI'll see if I can locate the fault of the capacitors, if it's still a problem, i'll let you know

author: viktor18
author_rank: Regular Contributor
timestamp: June 13, 2017, 01:34:24 pm
content: Quote from: bktemp on June 13, 2017, 01:12:18 pmAnd FYI, it's bad picture and the tracks are not damaged, the copper is just visible after removing a sticker.

author: StillTrying
author_rank: Super Contributor
timestamp: June 13, 2017, 07:47:17 pm
content: I can't imagine anyway the zebra connectors could cause that display.Of the 3 black diodes(?) below the caps, 2 don't look right compared with the 3rd one.

author: Samogon
author_rank: Frequent Contributor
timestamp: June 13, 2017, 09:07:31 pm
content: Easy to check, just swap with good one.