Blew a cap in NAD C521BEE, any advice? - diyAudio
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Old 11th July 2013, 06:56 PM   #1
scone is offline scone  United States
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Default Blew a cap in NAD C521BEE, any advice?

So, I blew a 1000uF cap in my NAD C512BEE CD player, and I'm trying to figure out what this is affecting and the importance of replacing it. My EE is a little rusty, haven't done any circuit design in a looong time, but the CD player seems to be working fine, and as far as I can tell the cap is there to smooth the Vout from an LM7808 +8V rail??? Is that correct?

The cap is the C508 capacitor from the schematics, and I've attached some pics of the blown cap and screenshots of the relevant portions of the service manual. As far as I can tell from the service manual, the +8V rail is only used for the display and control button circuitry? I would think replacing it is of fairly minor importance, but I'm curious if anyone has advice.

I don't know why it blew either, but it happened when the cd-tray was blocked from opening, but the button to open it was pressed. I can't see how this would have caused the cap to blow though, and it's possible these things aren't related...

Any ideas why this sucker went, and any advice about replacing it is very much appreciated.

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Old 11th July 2013, 07:03 PM   #2
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As an output capacitor of the 7808 it seems a bit on the large side. 10uF is quite normal there. More a question of why it blew ? Chances are the NAD is just very old. If I were you I'd recap all the electrolytics with the same values as originally designed. If you cant get the exact same value, use the closest value and next higher voltage.

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Old 12th July 2013, 06:45 PM   #3
Mooly is offline Mooly  United Kingdom
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Measure the voltage coming from the 7808 and check it for dry joints. An intermittent ground would allow the voltage to rise. Replace the electrolytics on the unregulated side feeding this reg and as K&D mentions, its worth a full recap particularly around the PSU. I would also replace the 7808 unless you are absolutely sure its OK.
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