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NAD C320BEE - Bad capacitors?
NAD C320BEE - Bad capacitors?
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Old 9th June 2019, 01:00 PM   #1
Holm422 is offline Holm422
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Default NAD C320BEE - Bad capacitors?

Hello dear forum members!

I have a need for your assistance!

I have a NAD 320BEE (with the infamous JH capacitors). I have read about them on Badcaps.net and read threads on this forum (1 and 2) regarding similar issues.

I am now facing the orange/amber light not turning green. I powered it off with the remote and I thought it sounded a bit louder than usual. And the next morning when powering on, the orange light stayed fixed - indicating something was wrong. Pulled the cord, waited and reinserted the plug and powered on with no luck. Still orange light. Unscrewed the lid. At first I thought the caps in the power supply / filter area had leaked but learned that this is just glue. I do think one of the 15000uF cap is swollen. Maybe some other ones are discoloured on the "mainboard". Could you please advise on what I might be seeing/not seeing? Should I just try to replace the 15000uF 50V capacitors or should I try to recap all electrolytics (with the possibility of shortening something). Previous during the last few years I have been hearing the 50hz hum but thought this was from the potentiometer since raising or lowering the volume made it disappear for a while.

I have a DMM and a soldering station and some basic knowledges but I do need some help in understanding how to think in approaching this type of issue. Where to begin? I feel quite lost.

Thank you for your time and effort!


Best regards,
Holm422
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Old 9th June 2019, 01:20 PM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Check for DC on the output firstly. If it has had regular use then the capacitors are probably not at fault, like a car battery not being used. L11 and L21 is a good place to measure from.
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Old 9th June 2019, 01:29 PM   #3
eduard is offline eduard  Netherlands
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Hello,
The big capacitors seem to have a plastic black foil to cover the aluminium can. You could try removing that by carefully cuttting it into pieces with a small stanley knife to check if the capacitor is really swollen. Maybe you could check with infra red thermometer is the one that looks bad has a higher temperature? Greetings, Eduard
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Old 9th June 2019, 01:42 PM   #4
Holm422 is offline Holm422
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Quote:
Originally Posted by JonSnell Electronic View Post
Check for DC on the output firstly. If it has had regular use then the capacitors are probably not at fault, like a car battery not being used. L11 and L21 is a good place to measure from.
Thank you for your reply and advice!

I checked the L11 and L21 with my DMM to DC, red on the coil and black on the chassi as ground. 0V on both, but when I put my probe on the L11 coil the black relay-looking thing produce a small jitter. Is this the way you inteded me to test? The 4 power supply fuses look good. What does this 0 V reading tell us, no power to the DC-side?

Quote:
Originally Posted by eduard View Post
Hello,
The big capacitors seem to have a plastic black foil to cover the aluminium can. You could try removing that by carefully cuttting it into pieces with a small stanley knife to check if the capacitor is really swollen. Maybe you could check with infra red thermometer is the one that looks bad has a higher temperature? Greetings, Eduard
Thank you for your reply and effort to try to help me! I do have a IR-temperature meter but sadly no battery. Read about the plastic top, but do I dare to cut in to them?
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Old 9th June 2019, 01:48 PM   #5
Holm422 is offline Holm422
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Amplifying information!

When measuring on the V+, V- and Gnd + Gnd connector from the power supply board to the mainboard the V- shows -29.5V and the V+ shows 51V. Does this help in any way to try to understand what is happening?
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Old 9th June 2019, 03:05 PM   #6
Leolabs is offline Leolabs  Malaysia
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Hi,just tell us between V+ and Gnd is how much and between V- and Gnd is how much.Dont worry about the polarity if you are using a Digital Multimeter.

Schematic is here :
https://3.bp.blogspot.com/-SShCymnrP...ower%2Bamp.jpg

I used to own the later version,C325BEE which the muting fet was dead.....so far no problem after sold to my friend.
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Old 10th June 2019, 06:50 AM   #7
Ian Finch is offline Ian Finch  Australia
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Originally Posted by Holm422 View Post
..... Read about the plastic top, but do I dare to cut in to them?
No need to. If the plastic cover alone is is bulged (as it often is) it will readily depress and return when you remove your finger. It the aluminium cap itself is bulged, you won't be able to depress the plastic cover, or not without considerable force, that is.
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Old 10th June 2019, 08:28 AM   #8
Holm422 is offline Holm422
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Quote:
Originally Posted by Leolabs View Post
Hi,just tell us between V+ and Gnd is how much and between V- and Gnd is how much.Dont worry about the polarity if you are using a Digital Multimeter.

Schematic is here :
https://3.bp.blogspot.com/-SShCymnrP...ower%2Bamp.jpg

I used to own the later version,C325BEE which the muting fet was dead.....so far no problem after sold to my friend.
Thank you for the schematics, I've been looking at the Reptips.dk C320BEE Service manual and this was a bit more easy to read for beginners.

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Originally Posted by Ian Finch View Post
No need to. If the plastic cover alone is is bulged (as it often is) it will readily depress and return when you remove your finger. It the aluminium cap itself is bulged, you won't be able to depress the plastic cover, or not without considerable force, that is.
The plastic cover is not depressable, a fraction of a mm is all I could get it to depress with use of some (but not extensive) force.

I did do a bit of measurements, could someone help guide me in what to make of it?

The orange light means "security". I read on this french blog regarding issues with the security module (google translate) and this gave me some insight.

I measured CB47 (value specified in schematics)
Pin 1 -> Gnd
Pin 2 -> 5.6 V (5.6V)
Pin 3 -> -38.5 V (-37)
Pin 4 -> 38.5 V (37)
Pin 5 -> 0.13 V
Pin 6 -> 1.75 V --> C421 --> IC 44 PIN 4 [1.75V] (2.0V)
Pin 7 -> 0V

CB49
Pin 1 -> -38.5V (-46V)
Pin 2 -> -38.5V (46V)

IC44
Pin 4 -> 1.75V (2.0V)
Pin 8 -> 3,23V (3.25V)

C420 -> 1.98 (2.16V)


There seems to be a substantial difference on the CB49 (7.5V difference), could this voltage drop be the culprit? Also when investigating the security part of the board on the underside (around Q41, C420, C421 and the resistorbank sourrounding these the board looks a bit discolored (yellow/brownish). Could not wash this of with IPA.

Thank you for any input!
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Old 10th June 2019, 01:01 PM   #9
Leolabs is offline Leolabs  Malaysia
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Quote:
Originally Posted by Holm422 View Post
Thank you for the schematics, I've been looking at the Reptips.dk C320BEE Service manual and this was a bit more easy to read for beginners.



The plastic cover is not depressable, a fraction of a mm is all I could get it to depress with use of some (but not extensive) force.

I did do a bit of measurements, could someone help guide me in what to make of it?

The orange light means "security". I read on this french blog regarding issues with the security module (google translate) and this gave me some insight.

I measured CB47 (value specified in schematics)
Pin 1 -> Gnd
Pin 2 -> 5.6 V (5.6V)
Pin 3 -> -38.5 V (-37)
Pin 4 -> 38.5 V (37)
Pin 5 -> 0.13 V
Pin 6 -> 1.75 V --> C421 --> IC 44 PIN 4 [1.75V] (2.0V)
Pin 7 -> 0V

CB49
Pin 1 -> -38.5V (-46V)
Pin 2 -> -38.5V (46V)

IC44
Pin 4 -> 1.75V (2.0V)
Pin 8 -> 3,23V (3.25V)

C420 -> 1.98 (2.16V)


There seems to be a substantial difference on the CB49 (7.5V difference), could this voltage drop be the culprit? Also when investigating the security part of the board on the underside (around Q41, C420, C421 and the resistorbank sourrounding these the board looks a bit discolored (yellow/brownish). Could not wash this of with IPA.

Thank you for any input!
It's "Protection",although didn't know why google would translate it to "security".

Anyway,this amp is powered by dual voltage level,i.e. when lower power it's running at lower supply voltage,if needed,it will switch to higher voltage.As far as i can see,it's that currently the supply is symmetrical in both plus and minus.

Try measure L11 and L21(doesn't matter which pin since it's almost zero ohm for DC) voltage respective to ground ,we need to check the is there any significant offset voltage at output.
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Old 10th June 2019, 10:27 PM   #10
Holm422 is offline Holm422
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Quote:
Originally Posted by Leolabs View Post
It's "Protection",although didn't know why google would translate it to "security".

Anyway,this amp is powered by dual voltage level,i.e. when lower power it's running at lower supply voltage,if needed,it will switch to higher voltage.As far as i can see,it's that currently the supply is symmetrical in both plus and minus.

Try measure L11 and L21(doesn't matter which pin since it's almost zero ohm for DC) voltage respective to ground ,we need to check the is there any significant offset voltage at output.
Thank you for helping me analyse the data!

As stated previously, the voltage on L11 and L21 is 0. Will test again tomorrow. What does this mean?
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