Something just occurred to me. The quote is only valid if the delay doesn't become too long during power down. Not only does it take longer to charge a bigger cap towards the threshold voltage, it also takes longer to discharge it below the threshold voltage.
When powering down, the relay should quickly switch off to prevent thumps. If you do hear strange sounds coming from the speakers when you switch off the amp, I'd recommend to use a 4u7 cap for C335 and a 10k resistor for R320 after all.
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Hi there!
Hello, this is going to be a long shot but I'm looking at a similar issue with my C315bee. It plays well for around 10 minutes, then clicks and go into protection mode. When it does, the audio is baerly audible in headphones even if the volume pot is cranked up. If at this point I turn off the mains switch, the audio comes back for a few seconds at full volume, then as the current discharge it dies. This could imply a protection circuit is in operation until the mains is switched off, am I right?
I'm a REAL rookie when it comes to electronics. I don't even own a multimeter but I'd love to learn some basic component replacements and know some soldering and I could borrow a meter. Are there any obvious replacements I could try to see if it will solve the problem? I have looked around the PCB for shorts or leaking caps without finding any. The two fat 10K uF 50V caps look a little bulged on top but not leaking. All other components look normal.
Sorry if this is too far fetched to even try to get some help, but a man can only try.
Any input will be appreciated.
Hello, this is going to be a long shot but I'm looking at a similar issue with my C315bee. It plays well for around 10 minutes, then clicks and go into protection mode. When it does, the audio is baerly audible in headphones even if the volume pot is cranked up. If at this point I turn off the mains switch, the audio comes back for a few seconds at full volume, then as the current discharge it dies. This could imply a protection circuit is in operation until the mains is switched off, am I right?
I'm a REAL rookie when it comes to electronics. I don't even own a multimeter but I'd love to learn some basic component replacements and know some soldering and I could borrow a meter. Are there any obvious replacements I could try to see if it will solve the problem? I have looked around the PCB for shorts or leaking caps without finding any. The two fat 10K uF 50V caps look a little bulged on top but not leaking. All other components look normal.
Sorry if this is too far fetched to even try to get some help, but a man can only try.
Any input will be appreciated.I removed some of the larger caps and figured I could try replacing them since they were bulging a little on top. The large 10000 μF ones were dry and had something moving inside when shaking them. Does anyone have ideas on how to remove the glue from the old ones? Heat with hair dryer? Chemically? Or just tedoiously scraping it of little by little?
I'll start by replacing the caps and see.
An externally hosted image should be here but it was not working when we last tested it.
I'll start by replacing the caps and see.
I guess I'm entertaining myself here, but what to do if the service manual says C310 is a 10 μF 25V cap but in it's place was a 10 μF 50V cap?
I guess replace with the same value that was there, a 50V one. But like, in case it's actually a humean error, like someone soldering in the 50V by mistake, would that double voltage be bad for the amp? I know that you can normally up the voltage, but since it's twice the value?
I guess replace with the same value that was there, a 50V one. But like, in case it's actually a humean error, like someone soldering in the 50V by mistake, would that double voltage be bad for the amp? I know that you can normally up the voltage, but since it's twice the value?
The cap voltage rating, as long as it is sufficient for the voltage of the circuit it is used in, has no relevance to operation. If it has been replaced previously or substituted with a higher voltage one in manufacture, it means nothing other than it could cost more but if you need to maintain more items in stock then it could actually be cheaper to have all one voltage type. All things considered - don't fret over trifling issues.
So.
I replaced about half of the capacitors on the board, all of the bigger ones and those close to the heat shields. Same problem.
Then I took some measurements on the pins of uPC 1237 protection module that was the source of OP's troubles. Could you help out? I feel a little anxious to desolder the uPC1237 since it mean further deassembly of the PCB from the chassis but I guess thats my next step... And perhaps ordering the orginal IC to replace it with the modifications - but before I do, is there something else I could do to diagnose? Here are the values (Volts):
It seems to me that the activation of uPC1237 is temperature related, since the amp can play for 3-10 minutes before the circuit is engaged? When the relay cuts the circuit, it doesn't come on by itself. I have to turn it off for a while and then back on for it to go out of protection mode. The current is slowly dropping on pin 6 while it cools off, or something. Any input would be appreciated! Thanks
I replaced about half of the capacitors on the board, all of the bigger ones and those close to the heat shields. Same problem.
An externally hosted image should be here but it was not working when we last tested it.
Then I took some measurements on the pins of uPC 1237 protection module that was the source of OP's troubles. Could you help out? I feel a little anxious to desolder the uPC1237 since it mean further deassembly of the PCB from the chassis but I guess thats my next step... And perhaps ordering the orginal IC to replace it with the modifications - but before I do, is there something else I could do to diagnose? Here are the values (Volts):
An externally hosted image should be here but it was not working when we last tested it.
It seems to me that the activation of uPC1237 is temperature related, since the amp can play for 3-10 minutes before the circuit is engaged? When the relay cuts the circuit, it doesn't come on by itself. I have to turn it off for a while and then back on for it to go out of protection mode. The current is slowly dropping on pin 6 while it cools off, or something. Any input would be appreciated! Thanks
UPC1237 is obsolete but clone replacements are available from China. Whilst they will work, there is no guarantee these clone parts are interchangeable so they work properly.
A protection chip is intended to prevent the amplifier from working, so I guess that's why there is a knee-jerk reaction to fix the protection when it is the the amplifier that is the likely cause. There is another possibility and it is common with amplifiers that run hot, which is that the timing capacitors in the protection circuit dry out and the relay won't close without them. Don't try to remove the chip, replace C320,332,354 first, if not already done as jitter may be suggesting.
NAD C315BEE Manual - Stereo Integrated Amplifier - HiFi Engine.
When that issue is settled, you need to check the amplifier health by testing the DC offset voltages across the amplifier output terminals (both channels) but likely before the relay if it still won't close. There should only be a tiny 50mVDC or less there.
A protection chip is intended to prevent the amplifier from working, so I guess that's why there is a knee-jerk reaction to fix the protection when it is the the amplifier that is the likely cause. There is another possibility and it is common with amplifiers that run hot, which is that the timing capacitors in the protection circuit dry out and the relay won't close without them. Don't try to remove the chip, replace C320,332,354 first, if not already done as jitter may be suggesting.
NAD C315BEE Manual - Stereo Integrated Amplifier - HiFi Engine.
When that issue is settled, you need to check the amplifier health by testing the DC offset voltages across the amplifier output terminals (both channels) but likely before the relay if it still won't close. There should only be a tiny 50mVDC or less there.
Hi, thanks for the reply. I already replaced C320, C332 and, can I assume you mean C334? There is no C354...
I also tried to measure DC offset but not sure I did it right. Here's what I did:
Speakers disconnected, I set the volume to minimum and no input connected. Then I measured the voltage at the speaker terminals. At first it looked alright, but after a while the voltage climbs to high levels:
Unit on - Both channels - first a healthy 2-3 mV then slowly rising to about 0.8 V before going into protection mode...
Did I measure it correctly? And, I guess this is bad right? I could keep on replacing the remaining capacitors of course, but perhaps there is a more pressing issue to be addressed? Please advice on how to proceed! I am very grateful.
Not sure how well it shows on the picture, but I indicated all the original (old) caps with a marker. The ones without are new. Are there any particular ones I should replace? Thanks a lot!
I also tried to measure DC offset but not sure I did it right. Here's what I did:
Speakers disconnected, I set the volume to minimum and no input connected. Then I measured the voltage at the speaker terminals. At first it looked alright, but after a while the voltage climbs to high levels:
Unit on - Both channels - first a healthy 2-3 mV then slowly rising to about 0.8 V before going into protection mode...
Did I measure it correctly? And, I guess this is bad right? I could keep on replacing the remaining capacitors of course, but perhaps there is a more pressing issue to be addressed? Please advice on how to proceed! I am very grateful.
Not sure how well it shows on the picture, but I indicated all the original (old) caps with a marker. The ones without are new. Are there any particular ones I should replace? Thanks a lot!
An externally hosted image should be here but it was not working when we last tested it.
Yes, and... There's this. When I soldered in C332, I think I accidently overheated or otherwise damaged the pcb pad a little. The solder didn't take properly and it must be due to missing copper on the pad... The bad joint is shown with a red arrow pointing on the + leg of C332 (outlined in green). Should I try to solder a connection to the + leg of C335 solder joint (blue) to make sure it's connected properly? Kind regards.
There's this. When I soldered in C332, I think I accidently overheated or otherwise damaged the pcb pad a little. The solder didn't take properly and it must be due to missing copper on the pad... The bad joint is shown with a red arrow pointing on the + leg of C332 (outlined in green). Should I try to solder a connection to the + leg of C335 solder joint (blue) to make sure it's connected properly? Kind regards.An externally hosted image should be here but it was not working when we last tested it.
Could bias/DC offset trimpots be something to look into? I followed the instructions in the service manual allignment procedure B to set the idle current. It was initially around 24 mV and I successfully set it to 7.5 mV after warmup. The protection circuit fired while adjusting the last fine trim pot but it didn't seem to affect the readings. As expected I guess but anyway.
Sorry for all the stupid questions...
Sorry for all the stupid questions...
Hm, yes and after adjusting the trim pots for idling current it now seems that it plays on... Been playing about 5 or 5 songs now without protection circuit engaging. Really!?
Surely this cannot have been only the idle current changing from around 24 mV cold to 7.5 mV warm? Must have been exercising the pot that stopped it from misbehaving in some way? Let's see if it sticks but so far, so good!
Surely this cannot have been only the idle current changing from around 24 mV cold to 7.5 mV warm? Must have been exercising the pot that stopped it from misbehaving in some way? Let's see if it sticks but so far, so good!
Hi smikko,
You might want to replace the trimmer controls. The DC offset controls would definitely cause the protection to operate if they are mis-adjusted.
Once you set the DC offset per the manual, watch it as things warm up. It shouldn't drift that much. A faulty offset control can cause that to happen, but so can other things.
-Chris
You might want to replace the trimmer controls. The DC offset controls would definitely cause the protection to operate if they are mis-adjusted.
Once you set the DC offset per the manual, watch it as things warm up. It shouldn't drift that much. A faulty offset control can cause that to happen, but so can other things.
-Chris
Yeah so I got the covers on and put it nicely with the speakers and all but now it's back to protection mode again. Back to work. Will do some new measurements on the TP1-2 and 3-4 pins I guess but I'd love some further help from you guys... 
How do I know if it's the trim pots or faulty tranistors or something else? I have a decent DMM and also a ESR meter beleive it or not, but I don't know how and what to measure... Any input would be appreciated!
How do I know if it's the trim pots or faulty tranistors or something else? I have a decent DMM and also a ESR meter beleive it or not, but I don't know how and what to measure... Any input would be appreciated!
Thanks, I will measure again and take another measurement as it warms beyond the 10 minutes the service manual refers to.
To sum up for anyone who can't be bothered reading back:
The amp engage the protection after playing nicely for a few minutes. After adjusting the idle current trim pots to service manual specs, it played for about 45 minutes before I turned it off without problems but now it's the same again. I replaced most of the caps. You can see which above. Measurements from uPC1237 legs above. I'm a newbie and tech, but not so electronics savvy. Fast learner. Need help.
BRB with measurments!
Took new measurements at the pins and the idle current is stable. Starts out around the 12.5 mV I set cold, then goes down to the 7.5 mV as it gets warm.
Can I assume the pots are ok by this?
That took around 10 minutes. After that the relay opens and voilá! Protection mode. But there's I reason I guess since there is DC at the speaker outs. Creeps up to 0.7-0.8 V then protects.
Can you assist me in further diagnosing this issue?
Thanks, have a nice morning/day/evening depending on location.
Here in Sweden it's after midnight on a cold and rainy summer night. Ideal weather and time for electronics work haha!
/Daniel
Can I assume the pots are ok by this?
That took around 10 minutes. After that the relay opens and voilá! Protection mode. But there's I reason I guess since there is DC at the speaker outs. Creeps up to 0.7-0.8 V then protects.
Can you assist me in further diagnosing this issue?
Thanks, have a nice morning/day/evening depending on location.
Here in Sweden it's after midnight on a cold and rainy summer night. Ideal weather and time for electronics work haha!
/Daniel
I read back a little and measured these according to what jitter said to OP a couple of years ago - and they both are within these specs. Diode 0.6 V and resistor 21.7 KOhm.
But not sure of the relevance since I figure the massive DC at output would be of more concern? What can be the cause of this?
Could I short or bypass the R330 thermistor somehow to see if that is what causes the relay to open? In that case how? The only resistor I have is a big 5W 120 Ohm one I use to discharge capacitors. Or is there another way to find out what causes the protection circuit to engage? Should be one of temperature or voltage right?
If one of the caps i didn't replace would be bad and leaking DC could that explain the voltage creeping up at the output terminals and could that happen slowly like in my case around 10-15 minutes?
If one of the caps i didn't replace would be bad and leaking DC could that explain the voltage creeping up at the output terminals and could that happen slowly like in my case around 10-15 minutes?
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