Dead/bad Caps in an NAD L40 - diyAudio
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Old 1st March 2007, 04:57 AM   #1
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Default Dead/bad Caps in an NAD L40

Hi all,

I've offered to look at why an NAD L40 (CD + Radio + 2x 50w) integrated AMP has stopped powering up.

I've checked the transformer and fuses and I'm getting all the right voltages - however I've found that the highpower stage (+/- 80v with no load) is triggered by a relay, which in turn is triggered by some logic on the board 'somewhere'. I same somewhere as I'm not quite game enough to remove the hundred odd little plugs that go to various things on the board - so I can trace it's route on the reverse side.

I've also not managed to find an L40 sevice manual online - so I have no idea what all the test points mean.

I started to look at it in the day light and found a bunch of caps - all the same brand but of differing values (between 1000 and 2200 uf) which appear to be leaking/have leaked.

Click the image to open in full size.
Click the image to open in full size.

Is it likely that these caps are the cause of the problem? It appears they're in the power supply for the digital stage of the board rather than carrying any signals.

Any help/advice greatly appreciated!
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Old 1st March 2007, 05:40 AM   #2
AKN is offline AKN  Sweden
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Hi raromachine,

Shown in pics is probably glue, used to secure heavy components.
Broken caps will usually bulge in the top before starting to leak.
/ Anders
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Old 1st March 2007, 07:56 AM   #3
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I guess the odd thing is that there are other bigger caps (68000uf) that aren't glued, and similar physically sized elna caps also not glued - hence why I thought it might be dried out electrolytic goop.

You're right - no bulging etc.

Back to the multimetering.
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Old 1st March 2007, 10:05 AM   #4
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Hrm - it appears the caps are fine and it's the plastic cased JRC 7812 that's died - its twin the 7912 is working fine by the looks but it's the 7812 that supplied the +12v most of the amp. Very CURIOUS Indeed!
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