cor wrote:Hi Degull,
I see that ZD53 and ZD52 are in series, so their voltages add up to give the protection voltage of 29V.
You can either take the part nr of the zener you removed, or measure its zener voltage by connecting it to your supply with about 10kOhm resistor in series.
Say that it shows it is a 12V zener diode and you want to raise the protection from original 29V to 34V (5V higher) that means that you need to add 5V to the zener voltage, either by adding a standard 5.1V zener in series or buying a zener with 5V higher voltage (for example 17V iso 12V)
You could raise the voltage to somewhere in the 34-35V so you still have a protection against accidental turning up the supply too high....
That was what I was thinking! I replaced ZD52 with a 20V zener and now my over protection is back. When the power supply hits 34.5V it goes into protection mode. I can now vary the voltage on the SP-500-24 between 22-34.5V with no worries about blowing it up.
I also have a SP-500-48 and the boards and layout are identical to the SP-500-24. I replaced ZD52 with a 30V zener in the SP-500-48 as well and now my voltage range is 38-63V with over voltage protection.
Thanks so much Cor!
Now if I could only figure out how to keep the fan running in a quite manner.