2018/10/29

SANSUI AU-5500 repair - 2

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Sansui's integrated amplifier AU-5500 manufactured in 1975 is being repaired.

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When removing the top panel and turning on the power, pilot LED lamp is lit properly. But the relay of the protection circuit is not released. Since smoke does not come out, I was relieved a little.

Then I heard something vibration noise from the inside. When I left it for about 3 minutes in this state, suddenly the vibration sound ceased, the protection circuit was canceled and the sound was outputted.
It does not distorted in a clear sound. But crosstalk performance are not very good feeling.

The problem is that the protection circuit is not immediately released, so there is a high possibility that something is happening around the power amp section. Therefore, I removed the bottom plate and observed the inside circuit.

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The board on which the metal can transistor is mounted is a power amplifier section, it seems to be orthodox configuration of single push pull amplifier.

A relay of the protection circuit was found here. It is quite suspicious about the protection circuit and the driver stage.

A little observation, I understood that the deterioration of parts of the electrolytic capacitor on this board has advanced considerably, and it seems to be the main cause.

Since this board is facing downward, it is easy to cause thermal deterioration of parts due to heat inevitably.
Although there are plenty of space inside the enclosure, it is mysterious why this configuration was made.

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This electrolytic capacitor, the electrolyte inside is expanded and is diagonal. Actually, the bottom half of the part is blackened with fever and the electrode is loose, so I think that it is on the verge of explosion. That vibration noise also seemed to be a source generated by this electrolytic capacitor.

So, I think that it is necessary to replace the inside of the deterioration parts in order. It should be repaired for each board separately as a whole. Fortunately, the power transistor seems to be alive, so it may be possible to replace with the minimum parts.

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I will clean up first because the dirt is stuck to the whole of this amp. Although only the front panel has few scratches, silver switches and knobs were stained in gold by cigarette smoke. It seems to have a long way to go.

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posted by toons at 09:11 | Audio