Hot-Air Rework Station Repairing

Last week, I switched on my hot-air station to do some soldering job. While I was doing other things, I smelled something. I noticed the smell is from hot-air nozzle. I switched off the station and checked that soldering nozzle is melted down due to overheat. Oop! what the hell is going on.

I quickly checked the problem. There is no air flow at the nozzle. But I still heard the air compressor  sound.

Hot air nozzle is melted down

Today, I tear down and find out the problem. My rework station is a cheap china made, LK852D brand. Here is what inside.

Hot Air rework station inside
Hot Air rework station inside

There are three boards, one step down transformer, one air compressor inside. There is nothing special, the right board is the controller board for hot-air nozzle and air pump controller. The left down side is the soldering gun controller. The left up side is a 7-segments display controller (3 digits display x 2 ).

hot air gun controller
hot air gun controller

This is hot nozzle controller and air pump controller. There are two Triacs, BTA136 , one for heat gun and one for air pump. There is also one IC, LM324 common opamp. The circuit is very simple. This is just Triac controller like a light dimmer. The Opamp LM324 is used to control Triac  with thermo-couple feedback, somehow comparator circuit like my previous soldering gun repair.

hot-airgun-repair (3)
LED Display and Soldering Iron controller

The upper circuit is 7-Segments display and the lower circuit is soldering iron driver. The 7-segment display driver IC is erased label. I don’t brother what’s inside these board for this moment.

The problem is the air compressor. There is no air flow. So, I removed the air pump outside the case and checked this. The controller of pump works well. The output voltage is measured and this can be controlled by the front panel knob. The noisy sound of compressor state that the driver is worked welled.

air pump take off



So, I open the pump by removing bottom side screw. This is diaphragm pump type. I quickly check that the both side rubber diaphragms are melted, leak  and damaged. Thus, the pump is not working well.

Air pump inside
Air pump inside


Damaged diaphrams
Damaged diaphragms


I cannot source locally the replacement part for this pump. But, I saw a guy is using aquarium pump in DIY hot-air gun.  The aquarium pump are also the same principle as the hot-air pump. Luckily,  I have this type of pump in hand. I bought this pump long ago to use with PCB etching tank but never use it. Good, now I have a good reason to use this.

aqurium pump


Opened the pump from down side, remove original AC cord and connected with driver output wires. This pump has dual output. I combine the two outputs easily to nozzle pipe like that. There is a air flow control switch beside the pump. I simply switch to high position.

Aquarium pump inside
Aquarium pump inside
replaced original AC cord and solder two wires
replaced original AC cord and solder two wires


Connect air pipes
Connect air pipes


Then sealed the two air output pipes inside the nozzle pipe with hot glue gun.

hot-airgun-repair (17)



hot-airgun-repair (18)

Attached the pump inside the case by cable ties.

Then, switched on and test the hot-air flow. It’s work. The hot air is flow out from heat element nozzle again.

hot-airgun-repair (19)



Finally results and  thought,

– The air flow is not strong as original compressor but it still work

– In most soldering case, the pump controller knob is required to set at 3/4 or 4/5 position. The air flow setting adjustment clearance is not so good.




16 thoughts on “Hot-Air Rework Station Repairing

  1. Thank you for sharing 🙂 I have the same problem, I will try to find a cheap air pump to replace the faulty one.

    I also had problem with a wire coming loose for one of the 7-segment displays, it was an easy fix, one of the wires to the display came off.

  2. if the pump triac had a shorted leg this would cause the pump to run in full throttle mode regardless of what the pot control on the front looked like right? I have a similar unit that has no current variable pump output and I can’t figure out why. I am starting to this that it’s a shorted pump triac. I didn’t realize that the pump motor ran through a regulator like that… I thought only the iron and hot air elements had triacs in line….

  3. I have the same unit and have been lucky so far with a few small exceptions. The flux on all boards needed to be cleaned majorly. The chassis ground although actually referenced to ground was not making contact. I put a proper ground terminal on after grinding the paint and checking connectivity. my only issue now in that the pump runs full voltage when in use. Does it make sense that of the pot is ok that the trial is shorted? ilI have continuity between the yellow and green pot wires and the terms at AIR2. Is the triac for pump control the one without the heat sink? Having a hard time following this circuit properly as it is pretty slapped together.

    Thanks for any help you can offer,

  4. Hello, I have a similar problem . I recently bought LK 702 rework station . Just As i turned it on ,the element of the hot air gun turned red hot and the station turned off after a few seconde due to safety fuse melt down. But now even after ive replaced the fuse only cold air comes out of the nozzle the hot air gun doesnt heat up.
    Any help on the subject would be appreciated. Thank you.

    1. Sorry for late reply,
      Seem your heat element driver not working. Need to check:
      1. Heat coil, check with multimeter Ohm line
      2. Driver component, it will be a SCR or IgBT depend on your model
      3. There may be a permanent thermal fuse in heat circuit, it may blow also
      ###Troubleshooting AC circuit may harmful. So, pls try with extra care.

    2. I am fairly certain that the element in your hot air gun will need to be replaced however the question is to find out why it went into thermal runaway mode. My guess would be that the MOSFET shorted out causing the circuit to be switched on continuously. If you replace the fuse, MOSFET, and the element, I would guess you would be in good shape. I accidentally ran my hot air gun without the pump when I was isolating circuits and it nearly destroyed the element without the air moving over it to keep it regulated somewhat. You will also need to ensure that you are getting air supply from the pump. Good luck and please respond with your findings/successes.

  5. there definitely should be a thermal cut off in the wand – mine doesn’t have one either as I briefly put power to the wand without the pump engaged and it began to smoke quickly and glow red. I may have to put a thermal fuse or something in the gun handle so I don’t burn my shop down…

  6. I have a very similar problem, but mine is that the airpump is working all the time at full speed, I mean, once you turned on the switch the 500k potentiometer does nothing to change thee flow amount. I have changed three times (threee different potentitiometers) but it still does the same. Any idea?


      1. Nop, never. It is funny, yesterday I was thinking about bringing it to the local store to see if they can fix it. There is only one position, full blow or nothing. A pitty because it blows away every component.


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