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Old 17th May 2004, 08:23 PM   #1
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Default Sanken 2sa1492, Onkyo


Hello,

I was charged to repair an onkyo amplifier. It holds a 2SA1492 and a 2SA3856 (on bot channels).

The amplifier fuse burns immediately at power on.
I disconnected the audio amplification unit, and so, suceed with power on the amplifier. So that I deduced that the PA unit is responsible for the short circuit.

I tried to reconnect it while the amplifier was powered on and off few second before( This way, the condenser are full of charge) .
I get a little claps on one of the seven pins; this allows me to guess (by following the circuit) that the 2SA1492 may be damaged and responsible for the short circuit of the unit.

However it does not looks like burned.

My question is ; should I try to test it to really know if it is burned ? How can I test it simply , in order to be able to say 'ok, it burned, and I may replace it ...'

Any comment will be greatly appreciated

Thanks a lot
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Old 17th May 2004, 09:00 PM   #2
boholm is offline boholm  Denmark
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Take out your multimeter - put it in resistance / short circuit mode and measure the resistance between leg 2 and 3 seen from the front (the side with the text on). If it beeps and/or measures less than 100 ohms it's dead.
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Old 18th May 2004, 07:42 PM   #3
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Default Transistor test

Thanks boholm

I will perform the tests this week end and you will be told of the results.
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Old 19th May 2004, 02:31 PM   #4
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You could also use the diode test function on your meter if you have that.

You should see a rising voltage on both transistors base to collectors, the pnp will stopping at around .5~.7v or so and the npn will continue to rise. Base to emiter should give somewhere between .05~.1v this however depends greatly on other circuitry in the amp (clamp diodes and what not) if any of the values come back zero I would remove it and test out of system and then you should see .5v~.7v b to c and b to e, or pins 1 to 2 and pins 1 to 3.
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Old 22nd May 2004, 02:54 PM   #5
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Default suggested replacements

if you fry them replace with 2SA1494 / 2SC3858 - if you fry them, i tip my hat
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Old 26th June 2004, 09:48 PM   #6
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Default IT IS NOW REPAIRED

Hi everybody,

I would like to thank all people who helped.
The onkyo amplifier is repaired, I replaced the transistors.
The job was done for a co-worker. I was very pleased to see the pleasure of the owner (and of course for free).

Thanks guys !
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