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.
Today, I tear down and find out the problem. My rework station is a cheap china made, LK852D brand. Here is what 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 ).
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.
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.
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.
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.
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.
Then sealed the two air output pipes inside the nozzle pipe with hot glue gun.
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.
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.