lcd all segments disappear after a while of turning it on - Page 1
Forum section: electronics / repair

author: abdolah
author_rank: Regular Contributor
timestamp: October 27, 2023, 08:59:43 pm
content: LCD IN MM-26 HIFI sound amplifier devicelcd all segments disappear after a while of turning it onlcd part no : AH7-10035Alcd driver : LC72362nPIN 55=lcd DRIVER SUPPLY power bias = 4.8v . test on board 4.8vpin 56=VLC 0=4.9v . on board test 4.4vpin 57=VLC 1=3.1v . on board test 2.3vpin 58=VLC 2=1.6v . on board test 1.2vthe problem is the disappearance of all the segments after a while of turning it on after replacing some caps the problem take longer to appearbacklight always onservice manualhttps://data2.manualslib.com/pdf5/118/11707/1170619-samsung/mm26.pdf?5b9666aa11c8a6af062235031239619b&take=binary

author: Swake
author_rank: Frequent Contributor
timestamp: October 29, 2023, 03:25:41 pm
content: Found attached datasheet for the driver LC72362N, but it does not match the table on page 9-11 of the service manual that you linked and nothing in the datasheet about driving LCD's. So, something is wrong here.Some other chips in the same family have LCD drivers. such as the LC7230 and LC72323 but it doesn't match the service manual either. Do you have any better information?Can you measure ripple on the power supply lines?Is anything running hot? If you do not have a thermal camera you can check for a heating using a quickly evaporating alcohol based solution such as IPA or lighter fluid. Apply the fluid over some area, then switch on the device, if the fluid evaporated quickly on one of the components then that is a suspect.

author: hummerjanne
author_rank: Regular Contributor
timestamp: October 29, 2023, 04:04:47 pm
content: Does your device have eeprom?

author: abdolah
author_rank: Regular Contributor
timestamp: November 01, 2023, 10:28:18 pm
content: no idont think so . it has a memory to remember the last settings for the volume and the equalizerbut not sure what does that do with all the segments disappearing

author: abdolah
author_rank: Regular Contributor
timestamp: November 01, 2023, 10:45:41 pm
content: the driver number is in the service manualno i don't have an oscilloscope unfortunatelyno nothing is getting hot .. no short . etcthe device is working but after a while of turning the device on and let it working for maybe an 1 hour this problem appears

author: wraper
author_rank: Unknown
timestamp: November 01, 2023, 10:53:06 pm
content: All segments disappearing could easily mean firmware crashing. If not refreshed, LCD will keep showing its last state but will fade away gradually. Or everything could disappear instantly, depends on how it's driven. LCD itself would not be my first suspect. Does everything else actually function besides LCD showing nothing? Sound may be still coming but can you say change the volume or do something else?

author: abdolah
author_rank: Regular Contributor
timestamp: November 01, 2023, 11:03:33 pm
content: yes everything else works fine even when the segments start disappearing the device is fully function . the buttons are responding no problems . the screen response is the problemwhen the problem starts when pressing any buttons some segments of the screen will appear and slowly disappear .. including the volume buttons . the text will appear and slowly disappearsame when holding the buttons

author: Swake
author_rank: Frequent Contributor
timestamp: November 02, 2023, 07:51:37 am
content: When you switch it off for about 15 to 30 minutes will it work normally again after that?You can try to re-solder all the connections of the LCD and the surrounding components.If the LCD is connected with a zebra strip then dismantle everything very gently, clean the strip with clear water and a very clean cloth.

author: tom66
author_rank: Super Contributor
timestamp: November 02, 2023, 01:55:34 pm
content: I think zebra strip is a possible problem too. Have you applied pressure to the front panel when the problem occurs, do the segments appear to fade in and out?

author: abdolah
author_rank: Regular Contributor
timestamp: November 03, 2023, 01:01:27 am
content: yes after the problem appear turning it off for Like haLf an hour and turning it back on will fix it but the problem will be back after a whileNO DRY solder JOINTS , I have re solder all the joints with fresh Solderthe screen is not connected via stripe it's connected using a CONDUCTIVE Glue

author: abdolah
author_rank: Regular Contributor
timestamp: November 03, 2023, 01:08:44 am
content: only when buttons pressedI will check again on the screen to see if it's connected via a stripe or notif it's I will clean it with some Isopropyl Alcohol and I will tell you the result

author: Swake
author_rank: Frequent Contributor
timestamp: November 03, 2023, 07:27:40 am
content: It points in the direction of a thermal issue or some charge building up over time.When the issue appears, try cooling down component by component to find out the location of the issue. Cool it with compressed air. Eventually you could use 99% IPA if you have a sprayer. Avoid using 70% IPA or similar on powered up equipment, this can cause shorts because of the water content.