Faulty 16x2 LCD Display? - Page 1
Forum section: electronics / projects

author: cameronhall
author_rank: Newbie
timestamp: May 20, 2025, 08:54:14 am
content: Hi,I've been investigating an intermittent fault where the main controller fails due to the 5V rail being pulled down to as low as 2.3V. This has been an ongoing issue, but the owner has recently captured some data following a fault event. The findings include:The 5V rail drops to around 2.3–2.4V.Thermal hotspots are visible on the bridge rectifier and, from what I can tell, the PTC fuse. The 5V regulator does not show excessive heat compared to these components.In one recorded fault, an ammeter in series with the 5V supply to the display panel measured a current draw of 60mA.The main control board reboots when the display cable is disconnected.In the most recent fault, a logging temperature probe placed on the TVS diode (located next to the PTC fuse) recorded a +20°C rise that lasted for 12 minutes before returning to normal. After this temperature rise, the control board continued to operate, but the display appeared to be damaged—specifically, the left half showed faded characters.I haven't been present during a live fault, so I’ve set up a logging system using a PC-based DAQ card, current amplifiers, and temperature sensors in the hope of capturing a fault to better understand the root cause. I've attached a basic layout of the control board showing where measurements are being taken.Based on what I’ve observed so far, the fault appears to be related to the LCD display. However, one point of doubt is the lack of heat coming from the 5V regulator—if there were a direct short on the 5V rail, I would expect the regulator to show more thermal activity.I’ve tested a board by loading the 5V rail until it shuts down, and in that case, the regulator does heat up significantly (see attached image "5V rail load test.jpeg"). However, I haven’t been able to simulate a fault that causes a consistent 2.3–2.4V output, as the regulator shuts off entirely if the input voltage drops below 3.6V.The display has been identified as a model from this manufacturer:https://www.av-display.hk/products/cob-moduleohckj/abc016002eThe logger also records the current draw on the four data and three control lines, in case a fault condition causes current leakage on those pins.I’m aware that connecting the logger introduces a ground loop, as it's using a PCI-based DAQ card in a PC, but I’m hoping this won’t prevent the fault from occurring. I've got a solution to run this from an PC with floating power supply if you think its a good idea but it requires a PCI adapter to be made.I’m expecting a faulty unit to be sent to me shortly so I can test it under controlled conditions with the logger attached. Hopefully, this will help confirm what’s going on. In the meantime, I’m open to any suggestions for further diagnostics, as the cause still isn’t entirely clear.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 20, 2025, 10:02:47 am
content: The PPTC is doing it's job and limiting the current, so nothing overheats and further damage is prevented.Apparently you have a thermal camera, so you can add a bench power supply (with current limit) to the output of theFULL BRIDGE RECTUM FIREand then carefully see which parts get the hottest.