SMD parts on Julia sound card blown. - diyAudio
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Old 7th February 2006, 03:49 PM   #1
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Default SMD parts on Julia sound card blown.

I fried some parts on my Julia sound card ( with180 volts dc !).
It looks like a transistor is blown open and a resistor is open ckt.
Left channel , output section.
The transistor has a marking MAX D7 ( Q5). The blown resistor (R130) seems to be 100 ohms . The Right channel is fine. Can't say if the 47uF /16V cap (C72) is dead ( seems to be OK ) and the JRC 4580 opamp (U23).
The high voltage was momentary as a loose output cable brushed past the pcb with 180 volts on it. There was an audible bang from the inside of my computer case.
I think the balanced section of the card might work.

Any idea what the transistor is and where I can get one? It looks like it is being used to mute the output.

Thanks for any help.
Cheers,
Ashok.
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Old 7th February 2006, 08:32 PM   #2
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If you don't have any resources to fix it, consider it dead and buy a new one. Luckily it's very cheap (in Sweden at least).
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Old 8th February 2006, 03:58 PM   #3
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I changed the damaged resistor and removed the ( mute?) transistor. The channel still does not work. Neither does the balanced input side on the same channel. So something common to both ends of the board .
Wonder if anyone knows what could be blown. The inputs are all OK.
Schematic or block diagram anyone ?
Thanks.
Cheers,
Ashok.
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Old 8th February 2006, 04:08 PM   #4
anatech is offline anatech  Canada
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Hi ashok,
Quote:
There was an audible bang from the inside of my computer case.
That sounds like high energy went into places where you don't want it.

Two things to check. One, have a good look at the card for blown ground or supply traces. Two, run the card in the computer where you can get to it. Finger test for hot chips. Watch out, you can leave skin behind if you aren't careful.

Sorry to hear about that happening to you. It just might be new card time.

-Chris
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Old 8th February 2006, 04:41 PM   #5
MikeB is offline MikeB  Germany
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Quote:
Originally posted by anatech
It just might be new card time.

-Chris
A new Julia ? Others buy a used car for that... (An old one)

Maybe the opamp is blown (very likely). Let's hope not more...

Mike
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Old 8th February 2006, 04:53 PM   #6
Eva is offline Eva  Spain
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In my experience, the damage due to that kind of disasters usually extends one layer past the visually damaged components. In other words, if your card has an analog mixer IC it may be partially blown. Otherwise, the DAC/ADC may be damaged
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Old 8th February 2006, 05:01 PM   #7
anatech is offline anatech  Canada
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Hi Mike,
I am not familiar to the "Julia". My comment was towards replacing it with *something*.

Hi Eva,
Normally you are right, but the damage could be worse. I look at this as being similar to a lightening hit. In seeking ground, the 180 V could have blown grounds, then travelled through the 5 V rails or 12 V rails to ground. This can take out everything in sight, even past the cracked or smoked IC's and one level back.

I hope this is not the case.

-Chris
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Old 8th February 2006, 05:10 PM   #8
MikeB is offline MikeB  Germany
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Sounds like to be that one: http://www.digit-life.com/articles2/...lia/index.html

As the other channel is still functional it's likely to be a smaller defect ?

Mike
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Old 8th February 2006, 08:25 PM   #9
Eva is offline Eva  Spain
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The block diagram may provide some hints:

http://www.ixbt.com/multimedia/esi/julia/scheme-big.png

The grey stuff between the DAC and the output buffer is what I called analog mixer. It's probably one of the ICs of the big PCB, altough it could be located in the smaller one instead. You should find out which one, get its datasheet to know the pinout, and check that it's actually outputing signal through both channels. If it's ok, then the problem comes from the output buffer.

Also, you may try reversing the big PCB in order to test whether the other set of inputs/outputs works properly or not.
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Old 8th February 2006, 10:29 PM   #10
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fwiw -- this is why I use analog opto-isolators -- IL300 from Siemens and HCNR200 1nd 201 from Agilent --
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