Please help me mend this power supply board. - diyAudio
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Old 21st May 2012, 11:49 AM   #1
diyAudio Member
 
Join Date: Mar 2006
Location: Cheshire
Default Please help me mend this power supply board.

Hi Gents

This is outside my normal area of experience (speaker building, DAC, digi amp builds). I hope that you can help.

I have a broken YAMAHA YSP800 sound bar. It does not turn on. I have another unit that works, and I have swapped over the power supply boards, and the broken one works, so I can safely say that the problem lies here.

Where do I start to find the broken component?

I have voltmeters, and a LCR meter.

Suggestions please.

Thanks.

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Michael
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Old 21st May 2012, 11:51 AM   #2
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When the working unit is plugged in, an audible click can be heard once from the box. When the broken one is plugged in - silence.
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Michael
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Old 21st May 2012, 12:01 PM   #3
yajnaS is offline yajnaS  India
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Join Date: Jan 2011
If it doesn't click, that suggests a fault in the standby power circuit. Check the mains transformer (the red one) see if there's a voltage on its output. Check the relay.

Last edited by yajnaS; 21st May 2012 at 12:03 PM. Reason: eh, that's not a soft start
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Old 21st May 2012, 12:02 PM   #4
spwalek is offline spwalek  United States
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Location: West Seneca NY
Check all the caps, especially the ones around or tied to the relay. That would be the click on the good one. I had a similar safety/delay circuit on a friends amp that caused the same symptoms and ended up being an off value cap tied to the relay.

Good Luck
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Old 21st May 2012, 12:28 PM   #5
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Location: Cheshire
Click the image to open in full size.

Ok. I have done some googling and it appears that this is a common problem with yamaha sound bars.

The 22nf 630v red capacitor to the right of the fuse is prone to failing. This cap on my broken board measures about half that of the one off the working board.

Can I use any kind of cap to replace it (22nf) 630v or higher. What is the difference between boxed caps, and the blobby looking ones?

Which of these would be suitable?

WIMA,MKP1J022203F00JSSD,CAPACITOR, 5%, 22NF, 630V | eBay

PANASONIC,ECQE6223JF,CAPACITOR, FILM, 630V, 22NF | eBay

PANASONIC,ECWH8223HA,CAPACITOR, 800V, 22NF, 3% | eBay

Thanks again
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Michael
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Old 21st May 2012, 06:11 PM   #6
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PANASONIC,ECWH8223HA,CAPACITOR, 800V, 22NF, 3% | eBay

that's the one i would use to replace the broken cap.
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Old 29th May 2012, 03:11 AM   #7
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Join Date: Jun 2007
Location: Phoenix, Arizona, USA
Did you check the fuse? (the one in the photo is clearly blown).
..
This brings me to the question: What component on the board went ballistic to cause the fuse to blow? Naturally, a really bad Capacitor could do this - but then you would notice the bulged cap.
..
Normally the output transistors fail and draw too much current (causing the fuse to blow).
(you check power transistors by using a diode test across the Collector and emitter leads - if it is blown it will be either open, or shorted. Shorted output transistors will generally be the cause of blown fuses, open transistors just don't work). Naturally, there are "other" parameters, but this parameter test is the simplest to locate shorted output transistors.
..
Check the Power Supply Rectifier Diodes (using the VOM measure the diodes with the leads across the diode, then reverse the leads. You should see a low resistance in one direction, and significantly higher resistance in the opposite - reversed - direction).
...
Dave
Phoenix, AZ
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Old 29th May 2012, 04:48 AM   #8
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Check the semi on the black heatsink.

Gajanan Phadte
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