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Shorted Transistors In Singer Active Speaker

By on May 6, 2020
singer active speaker repair

singer active speaker repair

The complaint of this Singer active speaker was unclear sound and low sound output. This problem can be due to the power supply producing improper dc output voltages or the main Amp circuit fault. Since we can’t guess where the fault is, I had to open up the cover and do a visual inspection check on the internal boards. The below photos are just how the internal boards look like:

singer active speaker mainboard repair

singer active speaker mainboard repair and fix

There seems no burnt components in both the power supply and the main AMP board thus before I checked on the components I need to discharge the main big capacitor first . In the below photo, C508 is the main filter capacitor. singer active speaker mainboard repair and fixing

After discharging the main filter capacitor I performed the test on main AMP output transistor.

I checked the transistor on board (below photo) and found that the reading was abnormal.

how to fix singer active speaker

Due to this I had to remove the transistor out of the board and checked it off board. True enough, the transistor (TIP42C) was shorted when tested it using Ohms range.

tip42c transistor shorted

tip42c datasheet

You may click on the above photo to visit the TIP42 Datasheet website

There was a pair of such transistors and since I already removed the first transistor, I took out the one and tested it. It was leaky too.

tip42c transistor shorted and replaced

There was no other bad components in the corresponding circuit.

I replaced only the two transistors and powered it up and the sound came back to normal again.

tip42c transistor bad in active speaker

Conclusion- When you have understood how to test and check electronic components using the right meters, you can practically try to repair all kind of electronics equipment. Before that, you must know the electrical safety to avoid being electrocuted. If you know how the circuit work and voltage/signal tracing…this could be an added advantage. If you are a beginners and wish to venture into this electronics repair field, I suggest that you get Jestine’s ebook in Basic Electronics Troubleshooting and Repair to start first as the information provided can cut short your learning journey. All right, will see you again in the next repair article.


This article was prepared for you by Suranga Bandara who owns an Electronics repair shop in Anuradapura, Sri Lanka.

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  1. Albert van Bemmelen

    May 6, 2020 at 11:50 pm

    Thanks for sharing. A good thing that those old TIP 42(C) transistors are still available for repair. In these times where mosfets and other new type of transistors are common goods the TIP bipolar types are ancient technology production wise.
    And if they were manufactured in long ago times when they produced that particular transistor serie in one go until another transistor type was made it could mean that they soon are no longer available like the old germanium transistors are also no longer produced or available.
    (Certain types of Germanium transistors are often still desperately searched for old Watchmakers clocks that often still run on batteries).

  2. babu ms

    May 7, 2020 at 12:19 am

    I am regular watching this newsletter and postings of your articles are very nice. I am already purchased the Jestine's E book. Thanking you and expecting eagerly for your many more articles please.

  3. Parasuraman S

    May 7, 2020 at 11:58 am

    As usual, a professional at work! Many thanks for sharing!

  4. Francisco Rica

    May 7, 2020 at 10:26 pm

    Good job Suranga. Could you remember what was your measures of the transistor on board? Could you explain why you suspect the transistor could be bad?? I imagine that you measure in Diode Mode.

    • Odd

      May 16, 2020 at 11:57 am

      How did you test in ohms mode to confirm the leaking

  5. Humberto

    May 18, 2020 at 10:23 am

    Good job Suranga.


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