This controller had a problem where a lot of digits at the top of the display were failing to show, which made adjustments impossible.
Opening up, I found the memory backup ‘battery’ (actually a 5.5v 0.33F supercapacitor) had leaked and corroded through some of the nearby carbon vias from the microcontroller to the LCD display
Getting corroded solder like that is really difficult to remove – it just doesn’t wet properly – the alkaline nature of the leak constantly fights with the acids in flux and with the heat just turns a hard black carbonised substance. Persistence pays off though and eventually removed the bad ‘battery’.
Measurements were made on all the suspect vias to confirm the worse, and prepped around 9 tracks for fine wire repairs through the vias (‘printed carbon’ like the pads for the LCD panel):
New backup supercap fitted after the fine strands of wires were carefully soldered in place.
Looking good!
