Comments on: Servicing Pioneer TX-520 Tuner

By: Humberto

Humberto — Mon, 28 Nov 2016 16:31:54 +0000

Good repair as usual, and thanks for sharing your articles.

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By: Ulises Aguilar Pazzani

Ulises Aguilar Pazzani — Sun, 27 Nov 2016 04:14:06 +0000

Mr Subramanian , great fix keep it up Sir

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By: Parasuraman S

Parasuraman S — Sat, 26 Nov 2016 14:10:30 +0000

In reply to Paris Azis.

A good suggestion! Perhaps I will try it, in the event it comes back! Thanks!

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By: Bulent NUR

Bulent NUR — Wed, 23 Nov 2016 16:27:06 +0000

Thanks for sharing, very skill.

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By: Alexan Catalin

Alexan Catalin — Wed, 23 Nov 2016 14:01:29 +0000

Hi Parasuraman.
In that case we have voltage doubling rectifier. (16.5V minus 12.4V) * current flowing out emiter Q10 is the power of transistor. Perhaps due to aging the current increasing and power is overlimit. Q10 being hot. Just measure the voltage of E, C and B, be like indicating in scheme. Heat sink is very good.
Thanks for sharing !

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By: Paris Azis

Paris Azis — Wed, 23 Nov 2016 07:10:20 +0000

Hi Parasuraman

If this unit soon comes to you again, you will certainly find out what the real culprit was...
Anyway, in this case, if I were in your shoes, before anything else I would use the freezing spray while having connected my volt meter across R58, that 4,7 ohm resistor connected in series with the collector of the regulating transistor. This would allow me to see the changes in current draw while spraying the suspected components. Most likely the problem would have been resolved in this way. I believe that this is the most effective method for troubleshooting such failures.
(I needed to download the schematic in order to follow up your thoughts about the case and then put my comment).
Thanks for sharing the case.

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By: Parasuraman S

Parasuraman S — Tue, 22 Nov 2016 21:50:11 +0000

In reply to Robert Calk.

Yes, did it with an oscilloscope, which is my routine check.

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By: Henrique Jorge Guimarães Ulbrich

Henrique Jorge Guimarães Ulbrich — Tue, 22 Nov 2016 13:35:36 +0000

Hi, dear Parasuraman. The problem of low-quality e-caps again. This subject was already approached many times here. It's not difficult, I suppose, to manufacture better quality e-caps. At the time of tube-equiped equiments, this didn't happen, at least so frequently. The e-caps of that time were better. As time goes, the tendency is to improve the components, but whith e-caps it seems to be the opposite! With regard to the hot transistor, the only occurrence I encountered was with a linear power supply that, by a reason I couldn't find, was oscillating. Knowing that e-caps does not function well at high frequencies (tending to present inductance in these cases), I easily solved the problem with the addition of a non-electrolitic capacitor at the output (in this case, it would be between emmiter of Q10 and ground).

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By: suranga Electronics

suranga Electronics — Tue, 22 Nov 2016 12:01:17 +0000

Hello, Mr-Parasuraman,

Nice Audio Tuner Repair.

Thanks Mr. Audio Expert.

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By: Yogesh Panchal

Yogesh Panchal — Tue, 22 Nov 2016 08:26:30 +0000

Higher leakage currents may cause the overheat; as advised by Robert sir check the frequency /Voltages and waveform on suspected area.

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