STK IC Tester

By on September 18, 2015
power audio transformer repair

 

 

 

 

 

 

 

I got one Sony FH-909R for service, with the complaint ‘no audio output’. On checking, it was found that the STK4152MkII was getting hot and high voltages were present in the speaker outputs, activating the speaker protection relay to shut it off. From my experience and after doing some preliminary check-ups, and also after noticing that the 34 V DC (dual supply) was dropping to 24V, I concluded that the STK is defective. So, ordered for one from UTSource and got it recently.

But on replacing the IC, the result was same! So, I suspected that it could be a fake IC, as is common in the market. Later, better sense prevailed in me and I thought why not I build one STK Checker, with a readily available assembled PCB made by Sri Guru, Delhi-6.This has all the leads etched in PCB pattern itself, and looked like a good one.  Please see pictures below:

power audio repair

power audio repair2

Now, the main draw back will be soldering the 18 pins on to this board every time and de-soldering it. As we all know, the board will not last longer. So, the next idea struck me as to why should I not provide an IC socket? But getting an 18 PIN single line IC socket is almost impossible. So, what I did was picking up an 18 pin dual line IC socket, cut it into two and solder it on to the board! Before that I checked whether the IC pins are properly aligned to go into this socket and found it was a perfect fit.  Please see picture:

stk ic tester

Then I provided three crocodile clips for the plus, minus and ground connections. Red wire for plus, yellow wire for minus and black wire for ground. The crocodile clips were selected as Red for plus, black for ground and ‘bare’ (removed its plastic sleeve) for minus.  Then provided speaker wire and two IP sockets for the speaker outputs. Please see picture:
power audio repair4
This board has two fuse holders in the speaker output. Then, with a PCB poker pin, I pushed each and every socket in the IC socket, to make room for the IC pins to go in smoothly.After inserting the suspected defective IC firmly into the socket (each leg has to be pushed in tightly with a tweezer), I rechecked all the connections.
As for the power supply, I used a 24-0-24 3A Transormer, with two 4700mfd/50V capacitors and 4 Nos. IN5408 Diodes, and fit this in a cardboard box. So, now I have a 30-0-30V 3A power supply!  Pl see picture below:
power audio transformer
power audio repair6
Then I powered it up.  When I checked the voltages at the output of the speakers, it was 0. So, switched it off, inserted two 1.5A fuses, and connected the speakers and switched it on. When I touched the inputs with a screw driver, loud noises were heard from both the channels, proving that the IC indeed was good! Now, I have to comb through the circuit of the Sony and locate the culprit that causes malfunction of the IC.
I am going to use this checker for checking a few other used STK series ICs (The circuits are common for almost all STK41 Series ICs) given to me by my friend long back! Hope this article will be of some use to my dear most Electronic hobbyists across the globe!
parasuraman
This article was prepared for you by Parasuraman Subramanian from India. He is 65 years old and has more than 30 years’ experience in handling antiques equipment Valve Radio, Amps, Reel Tape Recorders and currently studying latest techs classes conduct by Kerala State Electronics Technicians’ Association. He was a BBA graduate, retired as MD of a USA company and presently working as Consultant Manager, Purchase & IT, in Irinjalakuda Cooperative Hospital.

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You may check on his previous repair article below:

http://www.jestineyong.com/national-panasonic-rx5100-radio-cassette-repaired/

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16 Comments

  1. Gregory

    September 18, 2015 at 12:36 pm

    Great post ... Thanks!

    Likes(1)Dislikes(0)
  2. Gabriel

    September 18, 2015 at 1:29 pm

    Thank you for sharing it Parasuraman Subramanian. I too believe is a good idea to have an stk tester when you repair audio electronics

    Likes(1)Dislikes(0)
  3. skwong

    September 18, 2015 at 2:52 pm

    Very innovative ideal. STK series amplifier is not easy to trouble shoot & can damage easily. Is the amplifier test board available in the internet?

    Likes(2)Dislikes(0)
  4. Kissa

    September 18, 2015 at 4:14 pm

    reminds me when i used to struggle with stks, hope this is helpfull

    Likes(1)Dislikes(0)
  5. Martin

    September 18, 2015 at 6:21 pm

    Hi. Nice article.

    You could have obtained an IC ZIF socket from ebay and just used one side of it.
    E.G. http://www.ebay.co.uk/itm/28pin-ZIF-socket-for-DIL-ICs-Textool-0-3-Zero-Insertion-Force-narrow-DIP-/331647889270?hash=item4d37c12f76. I realise that this is the UK site, but they are a pretty common component.

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  6. Pepper

    September 18, 2015 at 10:29 pm

    Excellent job Mr. Subramanian!
    I wanted to expound on something you found, that is a potential on the speaker terminal. The output of the STK4152 is `Complementary-Symmetry' meaning a bi-polar power supply is uses and normally the potential at the direct coupled speaker terminal should be ~ zero DC. If either side of the output circuit shorts, the full potential (+ or -)will be applied to the speaker! Normally this will burn out the speaker voice coil! Always check for DC on the speaker terminals (-;

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  7. Corriete

    September 19, 2015 at 2:38 am

    hello sir. brilliant i must say. is there any chance you will share the schematic or is it on the net to be used by enthusiasts. thanks for sharing this

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  8. Albert van Bemmelen

    September 19, 2015 at 2:58 am

    Nice work Parasuraman Subramanian! I'm myself am not much of an Audio Repair man unlike you obviously are, but could you please next time also show the used Schematic of your STK tester you were telling about including the used Power Supply ? Because the Circuit was missing in your article. As also was asked by other readers in the Posts. I take it that you did use part of the Schematic that can be seen in one of your photo's as the STK tester that is common for testing almost all STK41 Series ICs? Because Google didn't give any clue on the mentioned info you gave.

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  9. Ulises Aguilar Pazzani

    September 19, 2015 at 9:28 am

    Excellent job Mr. Subramanian! great job

    Likes(1)Dislikes(0)
  10. Yogesh Panchal

    September 20, 2015 at 4:54 pm

    Good idea Sir, Thanks for sharing.

    Likes(2)Dislikes(0)
  11. bri

    September 21, 2015 at 1:13 am

    I used to work in a TV repair shop, the problem with the cheap STK's is they burn out after a few months. So be careful what you buy.

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  12. dicksy

    September 21, 2015 at 1:51 pm

    briliant idea mr Subramanian.good work
    thank you.

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  13. Parasuraman S

    October 12, 2015 at 2:14 pm

    1) The schematic was downloaded from website on a random search.
    2) That was used only to know the pin connections.
    3) The board is available in almost all leading electronic spare parts dealers, in major cities in India. I have no idea whether it is available online. Since the board has all markings on it, no need for a schematic.
    4) I did test the DC on the outputs and I am fully aware of the construction of STK ICs, as I have pried open a couple of them and traced what went wrong.
    5) Getting supplies to India from abroad is a very costly affair, mainly due to very high Courier Charges.

    I thank all of you for your encouragement!

    I always love to be at your Service!

    Best regards!

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  14. Vijay Thakur

    February 24, 2017 at 10:21 am

    I have STK 4231ll one and five 7294 amplifier so how much Apmr tarnformer I need. And how is power supply kit become I need 24/0/24 input in. The amplifier is 5.1 power
    For power supply capasiter no and diyod no plz send me

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  15. Arulmurugan

    October 15, 2017 at 11:01 pm

    I have problem in amplifier STK 4141 IC .I that IC speaker not working. How can I check that IC is working are not.

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    • Parasuraman

      October 16, 2017 at 3:51 pm

      Please fetch a ready board as described in my article. The outputs shouldn't have any DC present. That's the first test. The IC shouldn't get hot without load. If the IC is found to be OK, you have to check each and every component in the circuit for failure or abnormal values.

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