I bought a 2.hand.
I want to ask a question, Q155(2SD669)&Q158(2SB649) are very hot. They are 45C after 1,2 min. turn on. Also, they are power supply regulator transistor of somewhere 🙂 I don't know. But, they're not for power amplifier main supply.
In service manuel, in the circuit diagram it's 2sd669 (1.5A transistor), but in part list it's KSC2690AYSTU (1.2A transistor). In amplifier they used KSC2690AYSTU.
Is this normal NAD design (Too hot transistors)???
There is no problem in sound.
I want to ask a question, Q155(2SD669)&Q158(2SB649) are very hot. They are 45C after 1,2 min. turn on. Also, they are power supply regulator transistor of somewhere 🙂 I don't know. But, they're not for power amplifier main supply.
In service manuel, in the circuit diagram it's 2sd669 (1.5A transistor), but in part list it's KSC2690AYSTU (1.2A transistor). In amplifier they used KSC2690AYSTU.
Is this normal NAD design (Too hot transistors)???
There is no problem in sound.
Yes very common on a lot of amps. 45C is not that hot for most parts, as long as current is within that SOA at that temperature. I’ve seen a lot run closer to 55C and last for a long time.
If it gets over 60C and stays there, you probably have a problem, 45C is very likely how they built it.
If it gets over 60C and stays there, you probably have a problem, 45C is very likely how they built it.
If it is old, and you can, just refresh the heat sink compound if it has a heat sink, the compound tends to dry up.
Insurance...
Insurance...
Yes, some heat is usual. But, that's not usual I think? Please, look the service manuel.
R245, Q155, Q158 are hot, why R281, Q164 is so hot 🙂 R281 I think it's trigger out (12volt, measured 15v) and this jack empthy. This area on the board all hot. Br101 bridge revtifier little hot.
There are 2200uf capacitors. They're not looking good. But, I'm not sure problem is due to that capacitors. D123 15v zener, I measured 2.5V on it; is this bad?
Yes, yes it's bad 🙂 I found the one problem D123 dead. Now Q163, Q164, R281 are cold 🙂 I will think about Q155 side.. Thank you 🙂
R245, Q155, Q158 are hot, why R281, Q164 is so hot 🙂 R281 I think it's trigger out (12volt, measured 15v) and this jack empthy. This area on the board all hot. Br101 bridge revtifier little hot.
There are 2200uf capacitors. They're not looking good. But, I'm not sure problem is due to that capacitors. D123 15v zener, I measured 2.5V on it; is this bad?
Yes, yes it's bad 🙂 I found the one problem D123 dead. Now Q163, Q164, R281 are cold 🙂 I will think about Q155 side.. Thank you 🙂
Always nice to have a working side to verify voltages - should make short work of fault finding.
Good job finding the blown diode.
Good job finding the blown diode.
NAD c352 service manuel;
ALIGNMENT PROCEDURE (C352)
I. INITIAL ADJUSTMENT (No load connected)
A. OUTPUT OFFSET VOLTAGE
1. Connect a DC Millivoltmeter to L Channel speaker output terminals.
2. Turn unit “ON” and adjust VR101 (100ohms) to get a reading on IC107 Pin 1, which must be <100mV.
So what? I connect the voltmeter L channel. So, how can i get reading on ic107. Will I take another voltmeter? And some other variations 🙂 Can you please explain what I will do ?
ALIGNMENT PROCEDURE (C352)
I. INITIAL ADJUSTMENT (No load connected)
A. OUTPUT OFFSET VOLTAGE
1. Connect a DC Millivoltmeter to L Channel speaker output terminals.
2. Turn unit “ON” and adjust VR101 (100ohms) to get a reading on IC107 Pin 1, which must be <100mV.
So what? I connect the voltmeter L channel. So, how can i get reading on ic107. Will I take another voltmeter? And some other variations 🙂 Can you please explain what I will do ?
I think nobody understand NAD c352 service manuel!
I try some variations like, voltage between IC107 Pin 1 and active output terminal, output terminals, IC107 Pin 1 and ground.
What will you do if you're in my position 🙂
I try some variations like, voltage between IC107 Pin 1 and active output terminal, output terminals, IC107 Pin 1 and ground.
What will you do if you're in my position 🙂
What speakers are you using with it?
I had a c352, I tried about a half dozen different speakers on it (edit: not more than one pair at a time). I don't remember heat being any kind of stand out issue with it.
My current c326BEE now put on TV duty. I have 4 ohm bookshelf speakers running with it. It gets quite warm. I never had an amp get warm enough to call my attention,. This one did when I first got it.
Its been on running 24/7 for over a year. I never had any problems with it (knock on that wood).
Both of those ^ are excellent amps.
I had a c352, I tried about a half dozen different speakers on it (edit: not more than one pair at a time). I don't remember heat being any kind of stand out issue with it.
My current c326BEE now put on TV duty. I have 4 ohm bookshelf speakers running with it. It gets quite warm. I never had an amp get warm enough to call my attention,. This one did when I first got it.
Its been on running 24/7 for over a year. I never had any problems with it (knock on that wood).
Both of those ^ are excellent amps.
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Is this something you apply directly on the heat sinks?
I never heard of this before.
I only rely on fresh air to cool the sinks so they can do there job 🙂
Preamplifier of c352 is A class, It's power rectifier has 3 power transistors. two of them really hot (2sd669&2sb649). Also, amplifier section, R168&R158, 2.7k 2watts resistors are very hot. Of course I open and touched the parts.If we close the cover, it's little warm over the cover, upside of output transistors small coolers (again 2sd669, 2sb649) and preamplifier transistors little hot.
I draw; red very hot, > orange > yellow. Also, 5volt rectifier chip (LM7805) is not cold. I thing some of them, perhaps all is normal.
I used 8 ohms speakers.
I draw; red very hot, > orange > yellow. Also, 5volt rectifier chip (LM7805) is not cold. I thing some of them, perhaps all is normal.
I used 8 ohms speakers.
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Transistors are hot and heat sink is also hot. I don't think there is a problem in heat transfer between transistors and heat sink.
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Heat sink compound is a thermally conductive paste which closes the small air gap between components and heat sink, increasing the heat transfer and helping components run cooler.
Without it you can be in trouble.
Read up about it.
Without it you can be in trouble.
Read up about it.
Some $40 DVM have a thermocouple input. Buy a probe & use it. Yellow connector must match yellow socket.
Transistors <80 C are okay. Transistors will last longer @ 40 C but NAD is not a premium brand amp. You want 20000 hours life buy a Peavey, Crown, QSC or Yamaha PA amp. Preferably one made before watts inflation 2005 or later. I put bigger heat sinks and 2 fans in my dynaco ST120 with a reputation for toasting output transistors.
The oil in heat sink compound is necessary to spread it when applied. On old work, the powder is still there in the right places if the oil dries up. It has already been spread to correct places when applied. If you remove & replace heat sink from transistor, new compound including oil is necessary to move powder to the right places again. Don't use heat sink compound including metallic silver, like arctic. That is only for PC CPU's.
Transistors <80 C are okay. Transistors will last longer @ 40 C but NAD is not a premium brand amp. You want 20000 hours life buy a Peavey, Crown, QSC or Yamaha PA amp. Preferably one made before watts inflation 2005 or later. I put bigger heat sinks and 2 fans in my dynaco ST120 with a reputation for toasting output transistors.
The oil in heat sink compound is necessary to spread it when applied. On old work, the powder is still there in the right places if the oil dries up. It has already been spread to correct places when applied. If you remove & replace heat sink from transistor, new compound including oil is necessary to move powder to the right places again. Don't use heat sink compound including metallic silver, like arctic. That is only for PC CPU's.
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I agree. I found very hot elect.caps.. I think like you and I changed all caps for right side(for testing) and some common supply caps. Yes, some caps weak, but what was changed; nothing 🙂 I surprised. I will leave like that now, if somebody says my cooler are cold, not hot like for yours. I will think again.
I just read through this thread and I agree with you; this is a confusing set of instructions.
But I'd use the speaker terminal connections for measuring while adjusting VR101 for the left channel. And adjust to get as close to 0mV as possible....instructions say <100mV.
Do the same on the right channel using VR102 as per the instructions.
IC107 + IC108 (TL082BCP) opamps have the non-inverting input (pin 3) tied to ground. The inverting input (pin 2) is connected to + speaker post. So the output (pin 1) would the gained output from the difference of the inputs. I'm not sure if this opamp is just providing a "buffered" solution or actual gain, but I'd guess buffered. So ideally if pin 2 measures 0mV, pin 3 is 0mV (ground), pin 1 would be 0mV.
I recently restored a failed C325BEE which is quite similar to your amplifier. It was an ebay purchase, I knew it was DOA and there was attempted servicing (main filter caps were missing 🙄)
I replace every e-cap with NICHICON UKL or UPW (power supply) at 105C ratings. Many were failed / out-of-spec.
I stripped the chassis down to the main board for complete + easy access. This included removal of main heat-sink (output transistor removal, cleanup + reapplication of silicone grease). Being sure to use non-conductive silicone grease.
Also most every solder connection in the high-thermal areas was reflowed with new solder.
Sounds wonderful now.
I think there is a gain on the difference of the input, so not just a buffering of the input.
Still I'd adjust the trimmer pots for the lowest value on the DMM across the speaker binding posts.
OOOOOOOh yes, now I know what you meant! btw thanks.
How is the volume pot behaving with your C352 @ thread op?
Every "C" series amplifier developed a scratchy pot when adjusting volume. The wander slighly off centre and tend to drag in a couple places.
My only complaints about NAD amplifiers are petty. The speaker binding posts and the noisy volume pots. Both of which I learned to live with.
I did not know the C352 had a class A preamp. Same as the other one I mentioned previously C326BEE). I owned them a decade apart but remember it well. The smaller Bee reminds me of that one the most. Besides the power differences. The 352 vs the 326Bee.
There was the C355BEE made along side during the C352 run. Some people prefer the "lower" non Bee version. They are great sounding sweet amps.
Sounds like the heat issue was never an issue at all to be be concerned about. Keep on rockin' 🙂
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