Stanford SRS PS350 High Voltage Power Supply Repair

I received two PS350 power supply units that one of it has sparks when output is enabled and the other just won’t output anything at all.

The only repair info I found is from one of my favorite youtube channel the Signal Path. However, his unit has a much easier problem: the solder joints cracked because PS350 uses the metal case as a shield that are subjected to mechanical stress.

However, after difficult troubleshooting, I realized one unit has a fried resistor in the HV section, and a few core MOSFETs shorted.

The other unit is much more difficult: not only the HV capacitor is blown, resistor is blown, diodes shorted (won’t be able to detect it by probing in-circuit because of the capacitor ladder), PCB trace to the feedback path vaporized (without that the voltage will rise uncontrollably until something’s fried), and a bunch of MOSFETs, transistors and regulators ICs needs to be replaced.

Likely both units are broken because the users switched polarity without turning the HV section off (and let the voltage bleed out). This is very important and the markings on the case already warned the user NOT to do so.

You absolutely must NOT change the polarity while the output is live because the components in the HV section are marked for 4~6kV, so there is little room for a voltage spike past the operating voltages. The act of switching out the polarity (by mechanically swapping the pins through the dial switch at the back) doubles the voltage stored in the capacitors in a voltage multiplier ladder, so you are almost sure to crack the HV capacitors and likely the HV diodes.

Since I’ve developed experience for repairing SRS PS350, since I had to reverse engineer some of the circuit sections, I welcome request for repair evaluation (no fix, no fee). Please call me at 949-682-8145, or meet me at www.humgar.com.

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