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How To Repair Max 850 SMD Rework Station

By on October 27, 2017
how to fix and repair smd hot air machine










On  routine work at my workshop I found My HOT AIR SMD WORKSTATION having some problem. Air flow is OK But no hot air coming out of Blower.

I switched off the unit and switched on again here I found on varying the air control switch it works fine but on varying Heater control it does not respond.

how to repair hot air rework station

On normal working heater indicator blinks as you lower or higher the level. but here there is no sign of life. Hence I opened the unit for further diagnosis

how to fix rework station

So I have removed these two capacitors both the capacitors are out of range. 330uf capacitor shows 80.24uf.

how to repair rework station

Very fast I have diagnosed the problem and after replacing new capacitors i turned ON the unit but still the same problem.

Now it is time to give more attention on diagnosis so I have checked heater filament with meter it shows 99 OHM that means filament is ok .Then I have checked AC Voltages around 220V AC on Filament here I found that AC Voltage to the filament is missing. (You can skip this test – If Heater LED is not working that means there is missing Voltages from the circuit) So I have traced the circuit backward and reached to another suspect part. That is Triac part no. BTB08 600C this is 8amp 600v Max Pin out I found as follows.

rework station repair

so on testing the voltages on Triac I found 215V AC on middle leg. (It should approx 220VAC on both pin no. 1 & 2) So I have removed the Triac from the circuit and tested with meter it shows it as a resistor.

rework station fix

I have replaced the Triac with another value because I do not have same part with me. bad one is of 8amp And replaced with 12amp.


Now I have turned ON the unit again the same fault. Now I have started to trace and test the circuit and components. For tracing the circuit I used old method which works well in single layer PCB. By putting light under the PCB you can see traces from beneath as well connected components from the top.

how to fix and repair hot air machine

While testing surrounding components, on testing voltages I found the both the IC NE555N are missing. Working voltages on pin No.8 which is VCC Pin (5 to 18V DC).

(Advice to newcomers please makes practice of Testing Voltages on the circuit for any Electronics troubleshooting you will save your precious TIME).

ne555n ic data

Now on tracing the circuit I found one Zener diode located exactly beside the Capacitor which I have replaced before.

On testing voltage I found it does not show any voltage hence checked this diode with multimeter on diode test mode on the circuit it shows Ok but for my satisfaction I have removed the Zener and again when I checked with the meter look whit I found. Meter showed Reading on both the side

how to check diode

This is Indication of leaky Bad Diode

how to check zener diode

So I decide to turn ON the Unit without Zener diode for a moment and see the result. So I turned ON Unit without Zener and instantly I got the Heater LED Indicator light up and started to blink and checked Air flow through the handle I found hot air is blowing through.

max850 rework station repair

So I have replaced the diode it shows Value 4746 on googled I found this is 18V Diode. I have checked unit for 15 Mints. It works well without any problem.

So these are culprits…..

how to repair max850 smd rework station

This article was prepared for you by Yogesh Panchal who works as a Computer Hardware Engineer in Mumbai India.

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Note: You can check his previous repair articles in the link below:




  1. Parasuraman

    October 27, 2017 at 7:17 pm

    Very, very useful article. Many thanks!

    • Yogesh Panchal

      October 30, 2017 at 4:39 pm

      Thank you Sir.

  2. abigail karonga

    October 27, 2017 at 7:24 pm

    Thank you so much for clarity and clear pictures and well done congratulations for a good job only few technicians take time t repair their own tools

    • Yogesh Panchal

      October 30, 2017 at 4:40 pm


      Thanks for your Comment.

  3. Jusman Sulaiman

    October 27, 2017 at 7:49 pm

    I think that the Capacitor/Diode LCD Tester which I have never seen, is very important and very helpful. Please advise the price and where to buy

    • Yogesh Panchal

      October 30, 2017 at 4:46 pm


      This Meter is "MEGA 328" you can google it you will get this around 10 to 15 US$ Try ebay or aliexpress.

      • Yogesh Panchal

        October 30, 2017 at 4:47 pm

        Try to get it with testing hooks.

  4. maio

    October 27, 2017 at 8:47 pm

    thank you very much for your work.
    have a nice day

    • Yogesh Panchal

      October 30, 2017 at 4:47 pm

      Thanks Maio.

  5. R Murali

    October 27, 2017 at 10:01 pm

    Great Mr. Yogesh Panchal Nice to read your Articles and thanks for sharing with us your experience in this field.I am a regular reader of

    • Yogesh Panchal

      October 30, 2017 at 4:50 pm


      Thanks for your Comment.

  6. Suranga Electronics

    October 27, 2017 at 10:32 pm

    Hi.Mr. Yogesh,
    Very good well done..

    • Yogesh Panchal

      October 30, 2017 at 5:05 pm

      Thanks! Suranga

  7. Mihai

    October 28, 2017 at 1:20 am

    Hi, sir
    Good job ! I like the tester you used. Can you give an schematic or a website were can i buy it ?
    Thank you !

    • Yogesh Panchal

      October 30, 2017 at 5:07 pm


      Please. check above comments i have already given detail to Mr.
      Jusman Sulaiman.

  8. mahmoud_tajpour

    October 28, 2017 at 3:40 am

    dear Panchal thanks this is the best repair.

    • Yogesh Panchal

      October 30, 2017 at 9:54 pm

      Thank you Sir.

      • Sunil dutt sharma

        August 26, 2019 at 2:28 am

        Max smd rework station has failed after 10 years from whare i could repair it pls.give contact no for delhi

  9. Albert

    October 28, 2017 at 8:14 am

    Very nice article Yogesh. Those 1N4746 zeners likely are under-dimensioned being 1Watt types. Why probably the e-caps were destroyed after the zener collapsed. Or replacing the e-caps by higher max working voltages could prevent this from happening again too.
    Knowing that also 3Watt zeners exist it would be a good idea to replace it by these:

    • Yogesh Panchal

      October 30, 2017 at 10:14 pm

      Tanks for providing the Link.

      Indeed i have replaced bad diode with 18V 1W Diode.previously i think it was 1/2 watt.

  10. dhe kencoes

    October 28, 2017 at 9:18 am

    Good job Mr. Yogesh ! it's very useful for my reference.

    • Yogesh Panchal

      October 30, 2017 at 10:15 pm

      Thank you Sir.

  11. Robert Calk

    October 28, 2017 at 12:23 pm

    Good job, Yogesh.

    • Yogesh Panchal

      October 30, 2017 at 10:16 pm

      Thank you Sir.

  12. Luis Estrada

    October 30, 2017 at 1:07 am

    Very easy to follow explanation and good trouble shooting! I am also interested on details for the Max 850 but have not seen any posted yet. Is it the one at ?

    Also, helpful comments by Albert on October 28, 2017 at 8:14 am.

  13. Yogesh Panchal

    October 30, 2017 at 10:20 pm


    Yes this one is the same but you can have other models also you can visit the site

  14. Justice

    November 1, 2017 at 4:19 pm

    It is so interesting to read TO GAIN knowledge from you guys especially we the newcomers in the electronics industry, thanks a million Yogesh.

    • Yogesh Panchal

      November 3, 2017 at 12:18 am

      Your welcome Justice.

  15. Sonu Kashyap

    November 2, 2017 at 2:22 pm

    Good work...

  16. Yogesh Panchal

    November 3, 2017 at 12:19 am

    Thank you sonu.

  17. sumasumo

    January 15, 2018 at 5:36 pm

    Hie i would like to know the puporse of the white octo ic with 6 legs there... is it the one responsible for regulating the amount of heat coming out...

    i all the same enjoyed the post, thanks a lot, my problem is that too much heat is coming out of the noozle.. i cant control it..

  18. Amit kr Prasad

    June 21, 2018 at 9:56 pm

    Quick 850A air flow motor supply transistor number

  19. Francisco Rica

    February 14, 2019 at 5:41 am

    Good job, Yogesh.
    I enjoy much your your repair.

  20. Abhijit Paul

    March 17, 2019 at 1:55 am

    Sir..kindly providee me internal wiring Diagram for max850.


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