How to Repair the Lukey 898 Hot Air Soldering Station

By on October 15, 2016
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Repair and maintenance is an important issue when it comes to working with various types of soldering stations due to different damage and malfunction. In this article we will touch upon how to provide an accurate malfunction diagnosis and take repair measures of a broken Lukey 898 hot air soldering station as an example.




Basic Principles of Work with Hot Air Soldering Stations

The main obvious problem is that the hot air gun won’t heat up more than 22 °C and it’s impossible to be adjusted. To solve this task we need to use a screwdriver kit (Pro’sKit SD-2301), an oscilloscope and an analog soldering station. lukey-soldering-station-repair

First of all the soldering station under maintenance should be demounted and disassembled for further observation using Pro’sKit SD-2301 screwdriver kit. lukey-soldering-station-repairing

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The operational algorithm of a hot air soldering station is the following. lukey-solder-repairing

There is a heating element inside the handle with the 220 V voltage applied to it from the BTA 16 thyristor. Voltage of the control gate is transmitted from the 6th pin of the MOC3023 optical isolator with the 220 V voltage applied to it. Control impulse is transferred to the 2nd from the 15th pin of the PIC microcontroller through a R22 resistor. The optical isolator creates a galvanic isolation in the command circuit. The voltage of command circuit is generated in the PIC microcontroller according to the temperature set by the “Heater” controller.

To be more precise, the voltage of command circuit is picked from the comparator inside the PIC microcontroller. The chosen voltage is applied to one end of the comparator and the voltage measured from the optical isolator inside the hot air gun that is increased by the OP07 operational amplifier. The amount of impulses in the controlling output will grow until the voltages in comparator’s output and input become equal.

Hot Air Soldering Station Malfunction Diagnosis

Before starting the repair process it is important to delve into the question of how to carry out a precise and accurate test operation and identify the problem.

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The white and red wires on J2 connector are the contact elements of heated parts inside the hot air gun with an electrical resistance of 69 Ohm that means the device works properly. repair-solder-station-1

The J3 connector welds together two wires from optical isolator output an orange and a yellow one with resistance of 1.1 Ohm that indicates the optical isolator being intact. Now we can state, that the problem is to be searched for on the control board. repair-solder-station-2

Next the resistance on the 15th pin of the PIC microcontroller is to be examined. As we can see, the controlling impulses that are supposed to open the thyristor are present. The resistance of 5 Ohm corresponds with the closing of thyristor and 0 Ohm – with opening of thyristor. Also the resistance on the first output of the optical isolator is to be measured. It equals 5 V. repair-solder-station-3

And here we can also observe the oscillogram chart of the second output.  The current flows through the low-voltage circuit in the optical isolator, when the resistance on the output equals 0 V. When it equals 5 V the optical isolator closes.

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To examine the resistance between the 4th and 6th output in the optical isolator we need to connect the cold probe of oscilloscope to the 6th output of optical isolator. It is highly important to point out that while performing such measurements the oscilloscope should not be grounded. As we can see there is a 220 V voltage between the 4th and 6th output that indicates damage of the optical isolator. Using Pro’sKit 8PK-0313 desoldering wick, Interflux IF 8300-4 flux and a soldering station we can disassemble the broken element and then mount a new one instead. repair-solder-station-5

Now we need to test the results of replacement and the work of the soldering station in general. The new measurements indicate the malfunction was eliminated and the soldering station works properly. After the damage has been eliminated the oscillogram chart on the control points should be checked. Voltage on the J3 connector equals dozens of microvolt.  The OP07 operational amplifier increases it and on the 6th pin and the temperature set to 100 °C the voltage will figure up to approximately 400 μV. If the temperature increases, the voltage will accordingly increase as well. The opening impulses of the PIC microcontroller output are the impulses of 0 V. When the temperature goes up, the amount of impulses rises too. The voltage between the 4th and 6th pin in the optical isolator. repair-solder-station-6

The voltage between the cathode and anode of the thyristor. repair-solder-station-7

And again we make sure the soldering station works properly after repair.




This article was contributed By Toolboom.com

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8 Comments

  1. suranga Electronics

    October 15, 2016 at 3:19 pm

    Very Nice and good
    information Article.

    Thanks for Share it.

    Likes(0)Dislikes(0)
  2. Mark

    October 15, 2016 at 3:28 pm

    Well written and explained tutorial.
    Thanks for sharing.

    Likes(0)Dislikes(0)
  3. Parasuraman S

    October 15, 2016 at 5:07 pm

    Vow! Great! Highly professional approach! Hat's Off!

    Likes(0)Dislikes(0)
  4. Yogesh Panchal

    October 15, 2016 at 5:26 pm

    Thanks for sharing informative article.

    Likes(0)Dislikes(0)
  5. Albert van Bemmelen

    October 15, 2016 at 7:43 pm

    Thank you for the interesting repair with lots of detail! I wonder though if you had drawn any schematic before you were able to measure or investigate any of the Scope signals? The easiest way would be to check the components on another good working identical Hot Air unit with an Oscilloscope. Or just tested and/or replaced any of the not working components which probably would be the best way to start. After it would also be much easier to define the correct PIC processor signals and to check on any of the other components functions. My own two HotAir Solderstations sadly do not have any displays, so maybe are not exactly the same.

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  6. Robert Calk

    October 17, 2016 at 12:19 am

    Good job. Thanks for sharing the repair with us.

    Likes(0)Dislikes(0)
  7. Lad

    October 18, 2016 at 3:24 am

    Great article. Thank you for sharing.
    And what is the correct voltage between the 4th and 6th pin in the optical isolator?
    And can you please let me also know how you knew that some voltage values were correct( e.g.The resistance of 5 Ohm corresponds with the closing of thyristor and 0 Ohm – with opening of thyristor.)?
    Thank you

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  8. Lee

    October 19, 2016 at 1:52 pm

    when does one need to use un-grounded scope - please elaborate on this issue.
    great info in this artical, thanks.

    Likes(0)Dislikes(0)

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