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In the previous article , I covered the functionality and issues of the D400-007D 400V DC linear power supply by Oltronix.  In this second part, I'll describe the repairs and improvements carried out and also provide a link to the complete KiCad PCB project. Main high-voltage board  On the main high voltage board, the two main filter capacitors (C80, C81) were replaced with two 500 V, 100 µF capacitors. Although the original capacitors were still within specification, they were replaced to ensure reliable operation under modern mains conditions. Equivalent axial capacitors are expensive, so two more cost-effective radial capacitors were used (high-quality 105 °C types).  Two mounting holes were drilled in the PCB, and the capacitors were secured using cable ties. Jumper wires were then used to connect them to the original capacitor pads. The increased capacitance is not an issue due to the high resistance of the transformer secondary. It does not introduce significan...

Update, there is now also a part 2 .  This is another 1960s-era laboratory power supply from Oltronix. This article provides an overview of the design and highlights key considerations when repairing or restoring the unit. To ensure reliable operation on modern mains voltages, several components require upgrading or replacement. Below is a screenshot from the original LABPAC 30-series product presentation:           Front view.      Rear view with the EL34 series pass element visible.