Proper designs always include'bleeder resistors'to bleed off stored charge from the capacitors.
2.
:Have commercial power supply designs actually gotten so crappy that they no longer include bleeder resistors?
3.
While the power supply is on, a small current flows through the bleeder resistor, wasting a small amount of power.
4.
Large capacitors can actually recover a substantial part of their charge after being discharged by the bleeder resistor, if the resistor is not left in place.
5.
After it is switched off, the charge on the capacitor will drain off through this " bleeder resistor ", causing the voltage to decay quickly to safe levels.
6.
If the normal load cannot be guaranteed to perform this function, perhaps because it can be disconnected, the circuit should include a bleeder resistor connected as close as practicable across the capacitor.
7.
Often, a high-resistance bleeder resistor is connected internally within the flyback transformer to ensure the charge is safely grounded when not in use, but many sets lack this, especially older models.
8.
As a result, the large primary filter capacitor behind that rectifier was split up into two capacitors wired in series, balanced with bleeder resistors and varistors that were necessary in the upper input voltage range, around 230 V . Connecting the unit configured for the lower range to a higher-voltage grid usually resulted in an immediate permanent damage.
9.
I agree that this user shouldn't do the fan repair themselves, but no off-line switcher is going to hold charge on its electrolytic capacitors after " months "; the electrolytics are just too electrically leaky and even in the absence of deliberate bleeder resistors, there are other sneak paths that will bleed down the stored charge.
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