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Humax Set Top Box Fault Finding

By Jestine Yong on June 21, 2016

In my busy schedule in my office I got call from my home, my daughter complaining that the Cable TV was not working (summer vacation enjoyment with cartoon Channels). I have guided her some troubleshooting but the straight answer was, there was no power light indication in set top box. So I told her not to turn ON the TV or set top box till I reach home.

On reaching home in the evening I have checked the set top box and it was not working at all. This set top box is manufactured by Humax.

So I have opened the box for troubleshooting. There was no visual burn mark or any other physical damage on circuit board. I have checked power adapter with multimeter and it showed 12 VDC which was good.

Checked power section on PCB and I am not sure which component was this because checked with multimeter it was showing full continuity from both side assuming this is fuse I have moved further I am getting 12V on both the capacitors in power section that means power section is ok.

Rest of the circuit it is difficult to troubleshoot without proper Circuit diagram. The back side of the circuit board I found some SMD Components. Assuming transistors

On testing with Multimeter I found the entire transistors OK except 2X transistor

So right now I am near suspected faulty area but want to confirm by replacing the transistor if I can arrange form some old junk PCB because buying new one is not worth but to fulfill my curiosity diagnosed till these stage.

Till the repair my children’s are not going to wait hence ordered new Set top box because now school summer vacation is near to end.

Now I am looking for Circuit diagram. If anyone has some suggestions please share in the comments.

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

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Laptop Intermittent Battery Charging Fixed

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Set Top Box Repair

8 Comments

Albert van Bemmelen

June 22, 2016 at 12:29 am

Yogesh are you sure the X2 is a npn transistor?
They could according to their SMD code also be Zeners? In case of BZX99 a 13V 0.3W, or in case of BZX84 a 30V 0.3W, or in case of BZV49 a 30V 1W zener?
(all being sot23) See also http://english.electronica-pt.com/smd-databook?ref=x2
I did look for Humax on ElektroTanya but only found a interesting PDF with name :
humax_oak-ii-large_5100_5300_5350_5400_5500_5550_5600_5700_ver-1.0_sm

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- Albert van Bemmelen
  
  June 22, 2016 at 12:47 am
  
  Oops: the 2X instead the x2 is indeed only the 2N4401 type transistor.
  I guess it is just a question of replacing the bad one. But with those often badly standardized or hidden
  codes you never can be 100% sure.
  
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  - Humberto
    
    June 22, 2016 at 10:09 pm
    
    Hi Albert and Yogesh, here's another type of 2x (2X M) https://docs.google.com/viewer?url=http://www.onsemi.com/pub/Collateral/MMBT4401LT1-D.PDF
    
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    - Albert van Bemmelen
      
      June 23, 2016 at 5:53 am
      
      Hi Humberto. Indeed often the first characters of the components typenumber look like different typenumber versions of in fact just the same SMD Component. MMBT or STK or 2N are probably all the same NPN Transistor. I found the STK4401 several times in the Humax PDF Service Manual file I mentioned in these Post to be used for switching through electronic videosignals for Scart VCR, Scart TV and other connectors.
      (the f1-fox_service_manual_197.pdf)
      I had bought the 2014 edition Turuta SMD-code Book previously but still it is impossible to find all codes that exist. Some codes I still couldn't find anywhere.
      
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Yogesh Panchal

June 22, 2016 at 6:47 pm

Albert,
Here is the Link for 2X transistor
http://www.s-manuals.com/pdf/datasheet/k/s/kst4401_fairchild.pdf

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- Albert van Bemmelen
  
  June 22, 2016 at 10:26 pm
  
  Understood Yogesh! Must be equal to the 2N4401. I am afraid that finding a matching Humax Tata Sky Box Service manual will be very difficult. But often it helps to google the number and version of the printed circuit board used to find the much needed info. While searching for Humax T41 CPU B/D rev1.0 I found this Humax Service Manual that also uses the kst4401 transistor you mentioned. See this link: http://monitor.espec.ws/files/f1-fox_service_manual_197.pdf
  I hope this helps.
  
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Humberto

June 22, 2016 at 10:12 pm

Good repair Yogesh. Any published article is a source of information for readers. Congrats.

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Gautam

August 22, 2018 at 2:11 pm

Sir i purchase this book.iam headend owner and we have stb catvision and Surbhi.icannot able to repair STB.pls help

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