Hi,

There're other posts related this issue like this, http://forum.allaboutcircuits.com/threads/weller-wes51.93435/#post-1065641 but no solution found so far I guess.
My Weller WES51 is working only at 75F or higher. It gives me green light but the iron is not getting hot at all until I turn the knob to 75.
I did multiple testing based on the manual, "https://www.scu.edu/media/school-of...-lab-resources/Manual_WellerSolderStation.pdf"
Below is the test result.

Base Check
1. With line cord unplugged and power switch on, check for approximately 21 ohms at line cord blades
- PASS
2. With line cord plugged in and power switch on, check for 24VAC ±10% between pins #2 and #6 of tool receptacle
- 4.2VAC (#2 & #3 - 27.84VAC, #2 & #4 - 27.84VAC)
3. Check transformer secondary for 24VAC ±10% - 27.84VAC
4. Check wiring from tool receptacle to printed circuit board
- #2-red(bottom), #3-orange(2nd from top), #4-yellow(3rd from top), #5-ground, #6-red(top - J1)
5. Check for continuity from pin #5 of tool receptacle to line cord ground pin
- PASS

Tool Check
1. Check heater resistance from pin 2 to pin 6 (see Figure 1) of the tool connector, should measure 9 - 11 ohms
- 10 ohms
2. Check sensor resistance from pin 3 to pin 4 of the tool connector, should measure 1 - 2 ohms
- 2.3 ohms
3. Check resistance from pin 5 of the tool connector to tip, should measure 2 ohms maximum
- 0.4 ohms

One thing that's odd to me is #2 & #6 pins measured only 4.2V while #2 & #3 or #4 measured 27.84VAC.
Is this wrong?
The wire connections seem correct.
Can anyone help on this issue?

 

It's probably a Triac controller with a thermocouple in the tip, so there's a fault on the pcb or iron cable.

 

What use is a soldering iron below 75 degrees Fahrenheit?