If You Still Have Your Old Weller Soldering Gun Model D550 240 / 325 Watt, And If You Have Issues Of Keep Burning Up Switches In That Soldering Gun, Don't Trash It Yet, We Have A Quick Fix Remedy:

  The reason why that switch keep burning up is that old Weller soldering gun model D550 240 / 325 watt, that soldering gun's transformer is kicking back high voltage in several thousand volts that is burning up the switch that when that switch is turned right off, or switching between the low heat or high heat, and that switch is not tolerant to the inductive kickback of several thousand volts. So it's like operating an automobile motor without a distributor condenser in the ignition system that could burn up the distributor points or module that's by the inductive kickback from the ignition coil.

  The distributor condenser is a capacitor that store energy from the inductive kickback from the ignition coil, and transfer that energy back to the ignition coil to the spark plugs; and that's what that soldering gun needs, and it needs capacitors connected at the primary side of that soldering gun's transformer that would prevent that switch from burning up in that D550 240 /325 watt soldering gun. Here is that capacitor board that is installed in that D550 240 /325 watt soldering gun in the handle area in that pic at this link:

Old Weller D550 240 / 325 Watt Modification Pic

  The role of C1 in series with R1 are to help prevent the soldering gun's switch from arcing and burning up. The role of C2 in series with R2 are to help suppress the high voltage spikes from the soldering gun's transformer's inductive kickback. Each component can't work by themselves, and they all have to work together in order to prevent that soldering gun's switch from repeatedly failing. C1 value is so low, the capacitive reactance are around 265,000 ohms at 60Hz, and the current is in microamps when the soldering gun is off.

  So that old Weller D550 240 /325 watt soldering gun in that pic has been though 2 switches in before the modification was perform, and that's why that soldering gun in that pic was given away. Then after the modification and the 2nd switch was replaced, for over 6 months so far; that soldering gun in that pic never had anymore issues of that switch burning up and smoking.

Related Links:

Before Start Replacing The Switch
In Your Weller Soldering Gun
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