I probed and traced the following attached schematics of the HP HSTNS-PD43 server PSU's auxilliary(side) PCB(outer side only, of a double-sided multi-layered board). I devised a grid format so that descriptions of locations can be relatively easy.
Color Schematic With Hand Drawn Initial Feedback Traces for Voltage & OVP
Black & White Schematic Without Markings
Actual Auxiliary PCB![Resistors For OVP Mod: Carbon vs. Wire Wound - Different Results!? 2325571-2](https://www.eevblog.com/forum/index.php?action=dlattach;topic=435547.0;attach=2325573;image)
The color version of the schematic has red and blue hand drawn lines for (voltage mod / OVP mod related traces - initial feedback).
In C-10 and G-10 grid locations of the schematic, there are terminals marked "+12V+" which are feedback(vias) locations. If the blue lines are followed, one passes the point marked "<OVP HACK" this is where one end of the OVP mod resistor is connected (the other end is connected to ground). This OVP mod resistor has the effect of lowering the voltage at this point and as a result into the LM393 opamp(s), allowing for boosting the main output voltage from 12.3V to a higher voltage depending on the voltage mod resistor.
For the time being, for testing, I have wires soldered onto the volt/OVP hack points and the other end of the wires to a breadboard for testing with various resistors (carbon, wire wound etc.), and the breadboard's ground connected to the PSU's main output side ground tabs via alligator clip & wire.
In the schematic's D-12 location, there is the LM393's opamp A, and pin 3 (differential input +) takes the OVP sense related input signal voltage. I'm thinking that if the voltage at this input is higher than a certain threshold, the OVP triggers.
If a wire wound pot results in voltage spikes, shouldn't it rather support OVP triggering as opposed to it NEVER triggering?