Blown 100 Ω resistor fault

After 7 months of non-stop happy ppm operation bridge LCD got blank. Bridge was powercycled, LCD came back on and it seems ok, but after trying to start measurement it aborted with EM13 error. Further tests confirmed that it suddently stopped working and failed hard.

During self-test / calibration steps it also showing now crazy values -10000 for initial +/-1 Turn balance. Gain is also should be around -0.1, and not 0.00000.

Short investigation and troubleshooting revealed lot of magic smoke escaping from R17 100 Ω S102 Vishay resistor :(.

That bright blue-violet color of anodized heatsink with $140 USD APEX PA07 opamp also gives big concern, as it probably means heatsink was overheated to high temperatures caused anodize color to change from usual dark matte purple.

This resistor located on 6010T0101 Rev.2 PCBA, which is one of floating current sources.

Before desoldering:

Resistor turned to ash with metal bits inside. It measured resistance 0.5 GΩ afterwards, so poor 100 Ω element burned out completely.

It is standard $20 Vishay BMF S102A type resistor, manufactured in 49th week 1999.

Board overview (already with resistor removed)

Back of the same board. Wire hacks are original modification, condition as received.

Another main floating current source, board 6010201 Rev.8

This board is filled with expensive parts.

https://www.youtube.com/watch?v=ZJXwtGO-2Jw

Final photo – interconnect terminals: