SAUHING LEE wrote:

I 've just bought a used hakko 852 hot air smd rework station.

After i press the start button, the heater heat up and the air start
blowing(orange color from the heater). When the sensor detects the
desired temperature, there will be no orange color from the heater and
the air is still blowing.

I tried many times to remove a small diode with temperature at 420,
but the hot air is not hot enough. And the diode still stick to the
board(i test it with a tweezer)

This is the first hot air station that i has, so i don't know whether
the machines is defective or something is wrong?

Any suggestion?

When I was developing my homebrew hotair station
( http://www.cybertheque.org/homebrew/smt-rework-tool ) I found that
a few simple tests helped while setting temperature and airflow. These
tests are not intended to be quantitative, merely to indicate basic
functionality.

1. Basic temp test is to direct the airflow at a piece of bond writing or
typing paper at a distance of about one-half inch (13mm); it should
blacken a spot in one second at your chosen air velocity.

2. Use a scrap board with SMT components to experiment with air
velocity and temperature settings; airflow that doesn't blow away the
smallest components when used with the minimum temperature that reflows
the solder within a couple of seconds is ideal. Increase temperature
and airflow for larger components as determined by experiment. Note
the settings for production use.

It can't hurt to calibrate you settings with proper temperature probes
and pressure gauges. My station has an accurate low-velocity air gauge
but as of yet no temp. probes.

Michael