NAD C320BEE - Bad capacitors?

[Holm422]

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 here on the forum and I am now facing issues with my unit. 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.

Thank you for your time and effort!


Best regards,
Holm422

[andy1]

Re: NAD C320BEE - Bad capacitors?

This amp is very old and if the caps are the originals, they must have gone over the useful life. That cap on the first image looks bloated which is a bad sign. You may want to replace them altogether. Here is a link to the service manual. You have to make a free account on this site:
https://www.hifiengine.com/manual_li.../c320bee.shtml

[R_J]

Re: NAD C320BEE - Bad capacitors?

Download the manual for free here, no account needed

Sometimes it's just the plastic that domes a bit from heat, press on the plastic and if it moves down the cap is not bulged underneath, (it could still be bad)

[Holm422]

Re: NAD C320BEE - Bad capacitors?

This amp is very old and if the caps are the originals, they must have gone over the useful life. That cap on the first image looks bloated which is a bad sign. You may want to replace them altogether. Here is a link to the service manual. You have to make a free account on this site:
https://www.hifiengine.com/manual_li.../c320bee.shtml

Download the manual for free here, no account needed

Sometimes it's just the plastic that domes a bit from heat, press on the plastic and if it moves down the cap is not bulged underneath, (it could still be bad)

Used this and the above service manual. Https://3.bp.blogspot.com/-SShCymnrP...ower%2Bamp.jpg

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!

[R_J]

Re: NAD C320BEE - Bad capacitors?

I believe those voltages on C49 are normal under some conditions, The power supply can operates in low voltage output (+-38v) under certain conditions, when the amp fully turns on or higher power is demanded it will output a higher voltage (+-46)
The output voltage will be higher when the triger line is at 12v
Check your lower supply voltages +/- 18v, +/- 14 etc.
Check if there is any voltage on coils L21 & L11, these points are the output before the speaker protection relay and you should have close to 0 volts

[Holm422]

Re: NAD C320BEE - Bad capacitors?

I believe those voltages on C49 are normal under some conditions, The power supply can operates in low voltage output (+-38v) under certain conditions, when the amp fully turns on or higher power is demanded it will output a higher voltage (+-46)
The output voltage will be higher when the triger line is at 12v
Check your lower supply voltages +/- 18v, +/- 14 etc.
Check if there is any voltage on coils L21 & L11, these points are the output before the speaker protection relay and you should have close to 0 volts

I have a hard time understanding where to measure the lower supply voltages. I see them on the schematics but cannot figure where they are best measured. The L11 & L21 shows 0V on the 20V setting.

Thank you for your assistance!

[R_J]

Re: NAD C320BEE - Bad capacitors?

Does the amp turn on and do you here the relay click?
Check the voltage on the protection ic (ic44) pins 1 & 2 are the inputs and should be 0 volts, pin 4 is ac detect (C421) should be +2 volts, pin 7 should also be around +2 volts (C420), pin 8 is the vcc +3.25v, pin 6 is the output. You said that area of the board was discolored, if it runs hot those small elecrolytic caps are likely bad and dryed out (and will look ok)
What "orange light" are you refering to? I see red/green protection led or AMBER tape1 led all other leds are green.
Q41 is the +18 volt regulator transistor, Q42 is the -18 volt regulator. The collectors are the v in and the emitters are V out. If those voltages are off, I suspect the caps are bad in that area,

[Holm422]

Re: NAD C320BEE - Bad capacitors?

Does the amp turn on and do you here the relay click?
Check the voltage on the protection ic (ic44) pins 1 & 2 are the inputs and should be 0 volts, pin 4 is ac detect (C421) should be +2 volts, pin 7 should also be around +2 volts (C420), pin 8 is the vcc +3.25v, pin 6 is the output. You said that area of the board was discolored, if it runs hot those small elecrolytic caps are likely bad and dryed out (and will look ok)
What "orange light" are you refering to? I see red/green protection led or AMBER tape1 led all other leds are green.
Q41 is the +18 volt regulator transistor, Q42 is the -18 volt regulator. The collectors are the v in and the emitters are V out. If those voltages are off, I suspect the caps are bad in that area,

Thank you for taking your time helping me!

I rechecked the voltages on the IC44 nad C420, C421 and C422.

IC44
Pin1 0V
Pin2 80mV
Pin3 0V
Pin4 1,75V (specified 2.0V)
Pin5 0V
Pin6 0,5V (output)
Pin7 2,0V (specified 2.16V)
Pin8 3,25V (specified 3,25V

C420 - 2.0V
C421 - 1,75V
C422 - 80mV

For the brownish areas please see supplied images. Is it oriented front of IC44 circuit. And looks as it is mostly around the base of the heatsinks of Q41 and Q42 and the resistor/capacitorbank on the left (towards the transformer).

As of the light. It is the Power light. It is orange. Not red. It doesn't come out of "stand by". No reaction pressing the buttons on the front or the remote. No relay click.

Any good spots to measure the 18V supply on the board?

Thank you again!

[Holm422]

Re: NAD C320BEE - Bad capacitors?

[...]
Q41 is the +18 volt regulator transistor, Q42 is the -18 volt regulator. The collectors are the v in and the emitters are V out. If those voltages are off, I suspect the caps are bad in that area,

Read this a bit sloppy this morning and forgot about this:

Checked the emittors (and collectors) of Q41 and Q42
Q41 emittor 0V
Q42 emittor 2.5V

What I dont understand is that the soldering joints of the heatsinks the transistors are screwed in to are 37V.

The diod D043 has 4V both ways. Shouldn't diodes restrict the voltage one way?

[R_J]

Re: NAD C320BEE - Bad capacitors?

Q41 & Q42 collectors should have (+/-) voltage, if there is no voltage on either collector, check Resistors, R447,R449, then check R45,R46
You can check for + & - 37 volts on plug CB47 pins 1 & 2
Q41 collector should have positive voltage, Q42 collector should have negative voltage

what is "diod D043" Where is it located?

[Holm422]

Re: NAD C320BEE - Bad capacitors?

Q41 & Q42 collectors should have (+/-) voltage, if there is no voltage on either collector, check Resistors, R447,R449, then check R45,R46
You can check for + & - 37 volts on plug CB47 pins 1 & 2
Q41 collector should have positive voltage, Q42 collector should have negative voltage

what is "diod D043" Where is it located?

Hi!

Checked!
R45 38,7V
R46 -38,5V
Haven't found R447 or R449, yet.

CB47
38,5V and -38,3V

Misread the diode, it's D403.

Will locate R447 and R449.

Anything of this makes sense?

[R_J]

Re: NAD C320BEE - Bad capacitors?

Don't worry about R447/r449, if you have voltage on R45/R46 thats good
I would check the caps and resistors around Q41 & Q42, You should have +18v on Q41 (E) and -18v on Q42 (E)
If the caps in that area are bad I suspect you will not have the +_18v
Still can't dind D403

[Holm422]

Re: NAD C320BEE - Bad capacitors?

Don't worry about R447/r449, if you have voltage on R45/R46 thats good
I would check the caps and resistors around Q41 & Q42, You should have +18v on Q41 (E) and -18v on Q42 (E)
If the caps in that area are bad I suspect you will not have the +_18v
Still can't dind D403

Ok! I will check the caps!

[seanc]

Re: NAD C320BEE - Bad capacitors?

Hi,

What you will probably notice when looking at the capacitors is that most of the casing will be discoloured. When tested, I found most of the capacitors were not up to spec.

I completely re-capped one a few years ago and it worked as normal afterwards.