The transformer is manufactured by
Weiss. Primary 220 V, secondary 18 V. No information on the VA rating. Obviously the US models will have a different transformer.
![](https://www.eevblog.com/forum/reviews/weller-wha-900-hot-air-station-teardown/?action=dlattach;attach=270558;image)
The air pump is a turbine fan powered by a 3-phase brushless DC motor made by
ebm-papst. The part number is 939 3020 003. I was unable to locate a datasheet for it but apparently this model/series is nick named "turtle blower" and has a
blog entry on the ebm-papst website. Judging from that article the motor is most likely an
ECI 30.20. Nice little fella.
![](https://www.eevblog.com/forum/reviews/weller-wha-900-hot-air-station-teardown/?action=dlattach;attach=270560;image)
The spade connectors connectors carrying mains voltage have nice heat shrink tubing. What I did not like is that the bottom spade connector on the main power switch is not fully seated. It made firm contact but the security latch is not engaged and in theory vibrations could make it come off.
The circuit board is nicely laid out. (As seen from my annotated picture) the power supply is on the right side, center bottom is the triac drive of the heating element, top left the fan drive, and bottom left the microcontroller and some connectors. I was unable to dislodge the mains spade connectors from the board so I didn't take the board out for bottom view pictures but there are no components on the bottom side and nothing of interest underneath.
![](https://www.eevblog.com/forum/reviews/weller-wha-900-hot-air-station-teardown/?action=dlattach;attach=270562;image)
I'm not too impressed by the large Samwha electrolytic capacitor. You'd expect slightly better brands at this price point.
The fan is controlled by a
TB6551FG 3-phase full-wave/sine-wave PWM controller and 3
TPC8407 P/N-channel MOSFETs.
The heating element is controlled with a
BTA12-600C triac and
KTLP160J triac driver.
What surprised me about the heating element is that there are only 3 wires: Both ends of the element and ground. Where's the temperature sensor? The Weller documentation clearly states it's a closed-loop system with a temperature sensor near the nozzle. I did not attempt to reverse engineer the diagram but there seem to be more electronics than strictly needed above the triac drive so I guess Weller uses some trickery to read the sensor over the heater wires.
The brain of the unit is an unknown microcontroller labeled "Icwha_3" - I did not lift the label, sorry, but it's probably some PIC device. The unused red connector right above the microcontroller is most likely the programming interface. There's a mystery jumper directly left from the microcontroller - I have no idea what it's for. When shorted it's pulling one of the µC pins to 5 V but I did not have the guts to try it - for all I know it's to reset the calibration data.
Between the programming interface and the switch connector are a few unoccupied islands suggesting an optional second input for the microcontroller. Could this be for the version with foot switch?
There are more unoccupied islands between the power section and the fan drive - purpose unknown.
In the bottom left corner are two connectors. Apart from some extra diode protection both connect to the same pin on the µC through the
CNY75B optocoupler. Given the orientation of the optocoupler both connectors must be inputs? Maybe this is for the foot switch? Certainly makes more sense to have exactly the same PCB for both versions but why 2 different connectors?
I might take a closer look at this later. Maybe the foot switch input can be used to make the stand "smarter"...
![](https://www.eevblog.com/forum/reviews/weller-wha-900-hot-air-station-teardown/?action=dlattach;attach=270564;image)
That's it! I hope you liked this mini-teardown!