Another issue with my repair of this crane scale recently surfaced. There is a slow discharge of the batteries over time. I assume that this means there is a short somewhere in the circuit. The scale works and gives accurate weights. I have never been able to solve the display issue stated above but it would be nice to be able to leave the two battery packs installed without them draining over time.
The circuit board power comes from two separate battery packs of 4 D-cell per pack. They connect separately at U1 and the traces from U1 go in different directions and power different components of the circuit. As an example the negative side of one of the battery packs has continuity with the large electrolytic caps minus lead but the other pack does not. Yet this scale will run with just one (regardless of which one) battery pack installed. My assumption is the power to this board combines dual and single rail supplies to the various parts of the board and the weight sensor. Both battery packs get drained down evenly over time with the power off and the system will not work below 5.5v.
As a possible culprit is another suspected issue I raised in this thread(
https://www.eevblog.com/forum/beginners/how-to-determine-if-an-smd-board-has-shorted-component/msg1156767/#msg1156767) about a couple of smd caps that showed continuity across the terminals. I dismissed this as a possibility because of the last post in the thread and that scale works other that the display issue posted above.
I do not have a schematic but here is a picture showing the power terminals at U1. Any likely places that this short may hide?