Continuing with the TC1, I have one FNIRSI 324p-based (with power MCU as U8, transformerless, still with its factory firmware). It has a failure: Most of the times doesn't work, but sometimes work. I found the failure after I rubbed away the ugly whitened factory solders with alcohol. I had it on a drawer until recently.
Given the fact is not easy to find an ATmega unit, I'm trying to troubleshoot it. I describe its weird behaviour:
.-Most of the times get stucked with only "M-TESTER" message on screen. U6 (boost converter) generates 6.1V and the 78L05 4.9V. I can power it off by long-pressing the button
.-If it pass the boot banner, sometimes shows wrong (lower) battery voltage, and measures a phantom uF-range capacitor, sometimes between terminals 1 and 2, sometimes between 2 and 3
.-I already cleaned everything with alcohol or contact cleaner several times, and redo the solderings. While doing this, I found if I moisturize U6 with little bit of alcohol, it works for some minutes, with U6 delivering 5.9V
.-Sometimes works fine on its own
[EDIT]: Desoldering U6 and cleaning beneath it didn't solve the issue.
[EDIT]: I haven't found an Schematic of the transformerless variant to better study U6 behaviour here, In the meantime, I'm looking at the SB6284 datasheet.
Has somebody found/fixed an odd failure like this?