A German SIPOS electric actuator (economy type) at one plant went completely dead: no power indication, no display at all. Inspection confirmed the power section (power board) had failed; after replacing the board (control board untouched), commissioning went perfectly — everyone thought the case was closed. Three days later, the newly replaced power board failed again.
A single dead power board is routine: replace it. Two consecutive dead power boards almost certainly mean the root cause is not the board itself — the board is only the victim; something in the circuit keeps killing it. Peer analysis pointed in two directions:
1. A short circuit or ground fault near the power board: some point on the board shorted to ground or with degraded insulation, blowing each new board at power-up. The prime suspect is the installation environment: open the housing and look for foreign conductive objects — dropped copper strands, washers, burrs resting across live parts are the classic cause of "new board dies instantly";
2. Upstream stress on vulnerable components: peers noted that no-power-indication can also come from a failed thermal (sensing) resistor on the power board — and poor supply quality upstream (overvoltage, surges) can just as well kill board after board.
After two consecutive failures, complete these steps before powering up again:
1. Inspect the interior for conductive debris and for burn/arc marks, especially around the power-board sockets and terminals;
2. Megger the power circuit to ground; confirm no short, no ground fault;
3. Check the supply quality: is the voltage high, any surge/lightning history, anything else sharing the same supply;
4. Check whether the control board was already damaged in the first failure (untouched in this case — damaged components on it can in turn drag down a new power board);
5. Only then power up, and watch the new board's temperature rise closely (a related case: an IQ-series actuator with a fresh power board showed the silicon rectifier block heating up rapidly — further inspection found burnt components on the main board, which had been taking the new board down with it).
"A new board dies quickly" is the classic signature of a secondary fault: what is broken is not the board but its environment. The rule: when the same spot fails twice in a row, stop and ask why — do not simply replace again. Until debris, shorts/grounds, supply quality, and collateral board damage are ruled out, no third board should be installed.
