The Lincoln Welder SP‑150 G‑1687‑1 is an SCR (Silicon Controlled Rectifier) control board that manages power delivery and arc regulation in the welder’s 150 A DC output. Common failure points on this class of boards include burnt or tripped SCRs, degraded gate driver ICs, failed MOSFETs or IGBT stages, and damaged capacitors or inductors on the high‑current path; overheating from prolonged use can also cause insulation breakdown. First‑check diagnostics: verify that the input supply voltage is within spec and stable, inspect all solder joints and component leads for cracks or burn marks, and confirm that the SCR gate signals are present with a multimeter/oscilloscope before attempting any power‑on tests.[oss-gpt-20b]