Brax X1400 blown fets. Help. - diyAudio
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Old 1st December 2012, 12:31 AM   #1
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Smile Brax X1400 blown fets. Help.

I'm repairing this amp for a friend. But I've read online that brax amps have life time warranty with no worries about new owner. I notice it doesn't have a serial number so i guess sending it to the manufacture is out of the question.

My friend stated that his brother hook the power backwards and smelled something burning. Then never cut on.



Once i opened it i notice that the ground trace on the power stabilizer terminals shorted and the copper trace is lifted from the pcb. Three if the six power fets are obviously blown.


Any thing else i need to check before ordering fets and trying to fix the ground trace?

Thanks in advance.

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Click the image to open in full size.

Last edited by jeanious2011; 1st December 2012 at 12:48 AM.
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Old 1st December 2012, 02:30 AM   #2
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The gate resistors and whatever is driving the blown FETs.

Did you check the other power supply FETs? Even if they don't appear blown, they may be. They should be replaced regardless but if they're blown, you need to check their drive circuit as well.
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Old 1st December 2012, 02:41 AM   #3
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Thanks Perry, I've read your tutorial (got the full version) and successfully repaired a few with the help of Cecil and yours.

I planned on replacing all the fets. I'll check the drivers, i can't find the owners manual any where, I'm assuming the power stabilizer terminals are for some sort of capacitor (brax, duh,lol) but is it needed when powering up? Its just tied to the power input terminals, besides the ground since shorted/opened.
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Old 1st December 2012, 02:55 AM   #4
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If the terminals for the stabilizer are directly connected to the power and ground terminals, you're likely correct and it's for a cap. An external cap shouldn't be required for the amp to work properly.

If the amp has a reverse-protection diode, you should check it as well.
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Old 1st December 2012, 03:05 AM   #5
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It has it on power input terminals but not on the power stabilizer terminals hance that's probably why the grounded opened?
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Old 1st December 2012, 04:01 AM   #6
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It has what on the power terminals? An RP diode?
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Old 1st December 2012, 04:08 AM   #7
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Correction, i don't see any diodes on the b+ input. Why are the transformers covered up in those cases? Am worried the broken ground trace may short the case of the transformer, which the case looks metallic but i believe its plastic with a layer of electroplating.
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Old 1st December 2012, 04:36 AM   #8
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It sounds as if the case around the transformer is purely cosmetic.

Is the electroplating conductive?

Do you see any direct connection (with your multimeter) between the case and the trace?
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Old 1st December 2012, 04:48 AM   #9
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It fluctuates around 300 ohms on the casing. So am pretty sure its cosmetics. But that's where my damage trace is, right below the casing.

I don't see any rp diode by the power inputs. Check out the pics hopefully you can make out why it has a transformer between the power input and the power stabilizer terminals.


Click the image to open in full size.

Click the image to open in full size.


Click the image to open in full size.


Perry feel free to save my pics for your tutorial. If you need more let me know.
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Old 1st December 2012, 04:52 AM   #10
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Quote:
Originally Posted by Perry Babin View Post
It sounds as if the case around the transformer is purely cosmetic.

Is the electroplating conductive?

Do you see any direct connection (with your multimeter) between the case and the trace?
Yes but only if i lift the trace to where it touches the casing. That's why I'm curious to why use such casing? It fluctuates though and its around 300 ohms.
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