Author Topic: Repair of HiFi Amp - Transistor as a voltage regulator  (Read 1662 times)

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Offline riffmakerTopic starter

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Repair of HiFi Amp - Transistor as a voltage regulator
« on: February 22, 2019, 12:19:26 pm »
Hi All,

I am currently repairing an audio amplifier (Harman Kardon TA600), I discovered that one transistor was dead on the power supply board (I attach the diagram from harman, I highlighted in red the transistor that is not working anymore). The only information written in the user manual for this component is : 43029387 NPN power silicon. I tested each of the pin with a voltmeter before removing it, and it was 0V a the emitter

I desoldered the component and I unfortunately broke a pin, but I attach you a picture

Does anyone knows how I could replace it ? Which modern reference of transistor could fit ?

Thank you
Pierre
 

Offline dzseki

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Re: Repair of HiFi Amp - Transistor as a voltage regulator
« Reply #1 on: February 22, 2019, 12:27:24 pm »
Depending on the available space BD139 or BD239 would do. But the pinout of the transistor should be verified!
HP 1720A scope with HP 1120A probe, EMG 12563 pulse generator, EMG 1257 function generator, EMG 1172B signal generator, MEV TR-1660C bench multimeter
 

Offline jackthomson41

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Re: Repair of HiFi Amp - Transistor as a voltage regulator
« Reply #2 on: February 22, 2019, 01:49:26 pm »
Hi All,

I am currently repairing an audio amplifier (Harman Kardon TA600), I discovered that one transistor was dead on the power supply board (I attach the diagram from harman, I highlighted in red the transistor that is not working anymore). The only information written in the user manual for this component is : 43029387 NPN power silicon. I tested each of the pin with a voltmeter before removing it, and it was 0V a the emitter

I desoldered the component and I unfortunately broke a pin, but I attach you a picture

Does anyone knows how I could replace it ? Which modern reference of transistor could fit ?

Thank you
Pierre
yeah BD139, BD140 or BD137, they all can work and which one you select compare its pinout with yours.
« Last Edit: April 17, 2020, 02:29:04 am by jackthomson41 »
 

Offline riffmakerTopic starter

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Re: Repair of HiFi Amp - Transistor as a voltage regulator
« Reply #3 on: February 22, 2019, 02:18:48 pm »
Thank you for your answers !

Unfortunately, I checked with the original pinout, that doesn't fit... (I need the base pin at the center)

I found this reference : ZTX692B (datasheet attached)
Do you think that it could work ?
 

Offline Benta

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Re: Repair of HiFi Amp - Transistor as a voltage regulator
« Reply #4 on: February 22, 2019, 02:49:52 pm »
That looks a lot like a Motorola MPSU06 (NPN) or MPSU56 (PNP). Common in amps from the 80s. If you're lucky, you might find NOS parts somewhere.
 

Offline riffmakerTopic starter

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Re: Repair of HiFi Amp - Transistor as a voltage regulator
« Reply #5 on: February 25, 2019, 09:20:15 am »
Thank you Benta, you're right that seems to be that reference !

I now have to find some on the internet...  :D
 

Offline 6PTsocket

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Re: Repair of HiFi Amp - Transistor as a voltage regulator
« Reply #6 on: February 26, 2019, 12:10:57 am »
Did anybody notice that the 30 volt output is labeled 29.2 volts on the same wire if you follow it onto the circuit board?

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Offline bson

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Re: Repair of HiFi Amp - Transistor as a voltage regulator
« Reply #7 on: February 26, 2019, 12:38:19 am »
Also check C5.  If C5 is unable to hold a charge and effectively shorts, Q2 could be fried due to an excessive B-E voltage.
 

Offline alsetalokin4017

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Re: Repair of HiFi Amp - Transistor as a voltage regulator
« Reply #8 on: February 26, 2019, 06:38:26 am »
My old Interstate (Racal Dana) F43 function generator uses those same Motorola transistors as final output. After an... er... untoward event   :palm:   I was able to find NOS replacements at UTSource. They have always been good to me.
The easiest person to fool is yourself. -- Richard Feynman
 


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