Saturday, September 2, 2017

M-tech DVB-T2 decoder dead now repaired

I received a DVB-T2 terrestrial decoder and the complaint was dead, I applied the power and pressed on the power on button and indeed there was no sign of life whatsoever.

I checked the voltage across the bridge diode input and I got 240Vac according to the power grid here in Kenya and with that I confirmed all the circuit before this are working well.

I checked the voltage at the main capacitor and I got 328 Vdc and again I was happy with the reading



Then I jumped to the secondary side and tested the voltage across capacitor C85 (1000uf/16Volts) and I got 4.6 volts.

Since I had no circuit diagram to know the expected voltage on this line I considered the working voltage of this capacitor which was 16V and I concluded this voltage must be lower than expected and therefore I needed to continue troubleshooting what is causing this low output voltage on the secondary side.


I took my ESR meter and started testing the ESR reading of the capacitors on the primary side which were very few, in fact two only as you can see on the photo above.

The main capacitor was reading 3 ohms and since it was 47uf/400V I considered that to be okay, next I checked the ESR of the small capacitor next to the control I.C SW2604 which was rated 47uf/25v and I was shocked by the results as you can see on the photo below.


As you can see the capacitance of this capacitor is 44.70 uF and look good for capacitor rated 47uF, but what about the ESR reading of this capacitor? ESR=60 ohms.

A capacitor of this rating should not have more than 3 ohms ESR and now we are having 60 ohms… now you can see why ESR meter is not a good thing to have in your workshop but a must thing to have.

A tech with just a capacitance meter will have given this capacitor a clean bill of health but the ESR will pick it up seamlessly.

I picked a new capacitor of the same value and replaced and after applying the power I was happy with the results as you can see below.



The decoder is now powering after replacing just one small capacitor, I believe in most cases most electronics gadget end up in dust bin due to very small problems and if Tech can invest in good test equipment then this can be reduced drastically.


Thank you guys.
See you in my next class 

6 comments:

  1. i agree with you as i solved many problems with the esr meter
    BASHEER


    ReplyDelete
    Replies
    1. Thanks for your feedback Mr Khan and for passing by.

      Regards Humphrey

      Delete
  2. very nice job, you can catch the culprit easily.pls. give me more articles of repairing in your experience. thanks! ruben

    ReplyDelete
    Replies
    1. Noted and thanks for passing by Ruben
      Regards Humphrey

      Delete
  3. Thank you again for very useful repair information.

    ReplyDelete