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 stopped working and failed hard. This was probably caused by the incorrect connection at the terminals causing excessive current flow.

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:

Projects like this are born from passion and a desire to share how things work. Education is the foundation of a healthy society - especially important in today's volatile world. xDevs began as a personal project notepad in Kherson, Ukraine back in 2008 and has grown with support of passionate readers just like you. There are no (and never will be) any ads, sponsors or shareholders behind xDevs.com, just a commitment to inspire and help learning. If you are in a position to help others like us, please consider supporting xDevs.com’s home-country Ukraine in its defense of freedom to speak, freedom to live in peace and freedom to choose their way. You can use official site to support Ukraine – United24 or Help99. Every cent counts.