Now all the caps on the right amp are changed.
Reconnected it late last night to try it out, but when I started the amplifier it died in a fraction of a second. Tried to disconnect the right amp but the amplifier is still dead.
No idea what I did wrong and it was too late to look for the problem.
Didn't take that many pictures this time due to a bit too eager. Big no-no...
Let's start with the mistakes in text though.
The caps I ordered for C422/423 had to thick leads, so I had to drill the holes a bit bigger (0,5 mm to 0,8 mm), no biggie.
The caps for C411/412 should have been rated to 105C. Had noted that and written it in the list, but I still ordered 85C somehow. Those are the black ones to the left.
There are mountig holes for four caps, so I changed to the outer holes to get a bit more air arround them.
For the coupling cap I soldered leads on the back of the card. By doing this I can fit any cap I want, and I can change it by just popin' the hood. Is Mundorf EVO a good choice if I want to keep it under 15€/cap?
Thermal paste, don't forget that!
I used some old tube that I rejected for the CPU/GPU years ago. Still better than the pads for sure.
And here it is!
So, back to my problem.
Can I damage something by trying to start the amplifier without the right channel connected?
Since that's the only thing I've touched sice it worked, the problem should be there.
Reconnected it late last night to try it out, but when I started the amplifier it died in a fraction of a second. Tried to disconnect the right amp but the amplifier is still dead.
No idea what I did wrong and it was too late to look for the problem.
Didn't take that many pictures this time due to a bit too eager. Big no-no...
Let's start with the mistakes in text though.
The caps I ordered for C422/423 had to thick leads, so I had to drill the holes a bit bigger (0,5 mm to 0,8 mm), no biggie.
The caps for C411/412 should have been rated to 105C. Had noted that and written it in the list, but I still ordered 85C somehow. Those are the black ones to the left.
There are mountig holes for four caps, so I changed to the outer holes to get a bit more air arround them.
For the coupling cap I soldered leads on the back of the card. By doing this I can fit any cap I want, and I can change it by just popin' the hood. Is Mundorf EVO a good choice if I want to keep it under 15€/cap?
Thermal paste, don't forget that!
I used some old tube that I rejected for the CPU/GPU years ago. Still better than the pads for sure.
And here it is!
So, back to my problem.
Can I damage something by trying to start the amplifier without the right channel connected?
Since that's the only thing I've touched sice it worked, the problem should be there.
No?
I thought the mosfets should not have any electric connection to the cooling plate. Do I need to isolate them in some way?
Found out that my electric grid filter died, so thats why I didn't get any power.
Gonna tear down the amp again and check it thoroughly, like I should have done at the first place.
Maybe.
Shouldn't have been that great of a connection since the thermal paste is non conductive, but it might have been enough...
Found out that there is a short between pin 1/2 (VOP R) and 5 (-64V) in the power connector.
Not sure where though.
With the board disconnected.Is the short towards the amp board or with the amp board disconnected?
If on the amp board it may look like shorted output transistor(s) 2SC5200. Warning: Noob
If I can't find anything obvious, I can start with them.
You were right, one of them is shorted!Is the short towards the amp board or with the amp board disconnected?
If on the amp board it may look like shorted output transistor(s) 2SC5200. Warning: Noob
With the 2SC5200's removed the resistance between pin 1 and 5 is 1k instead of 0,1.
The left amp with the transistors still in order has 480 ohm, so it sounds right.
When I meassure them, the others are like this.
Should be ok?
I'm back!
I checked all transistors and caps in contact with the short circuit but didn't find any more damaged components. Changed the shorted transistor and it powers up.
According to the manual the amp should be adjusted at start. The values was within specs right away (+-3V), but I got it a bit closer to 0V.
Have been listening and used the balance to shift between the original channel and the serviced and I find the new sound warmer and more detailed. Feels like the artist is in the room and not at an stadium.
Now I will take care of the left amp and order some input caps.
I think it will be these: https://www.audiophonics.fr/en/mund...f-mcap-evo-oil-capacitor-450v-10f-p-7300.html
I checked all transistors and caps in contact with the short circuit but didn't find any more damaged components. Changed the shorted transistor and it powers up.
According to the manual the amp should be adjusted at start. The values was within specs right away (+-3V), but I got it a bit closer to 0V.
Have been listening and used the balance to shift between the original channel and the serviced and I find the new sound warmer and more detailed. Feels like the artist is in the room and not at an stadium.
Now I will take care of the left amp and order some input caps.
I think it will be these: https://www.audiophonics.fr/en/mund...f-mcap-evo-oil-capacitor-450v-10f-p-7300.html
Finaly done!
Took a few weeks to get the Mundorf caps since they were out of stock.
Started to upgrade the home cinema instead while waiting so this got a bit extra delayed.
Started with the untouched left amp and did a full recap and installed the Mundorf so I could benchmark it against the right one with Elna coupling cap. What a difference!!
Now when I'm done with both, all that's left to do is get all documentation in order.
I'm so happy with the new sound and I'm pretty sure that it didn't sound this great when it was released.
Thanks again for all guidance!
Couldn't have done it without you guys!
Took a few weeks to get the Mundorf caps since they were out of stock.
Started to upgrade the home cinema instead while waiting so this got a bit extra delayed.
Started with the untouched left amp and did a full recap and installed the Mundorf so I could benchmark it against the right one with Elna coupling cap. What a difference!!
Now when I'm done with both, all that's left to do is get all documentation in order.
I'm so happy with the new sound and I'm pretty sure that it didn't sound this great when it was released.
Thanks again for all guidance!
Couldn't have done it without you guys!
loved reading this great work finding problems can be very frustrating once you solve it the reward is hearing that nice crispsounding amplifier working as intended I know NAD suffered from. inferior quality parts but their designs are Good and many who dissed their products once they had opportunity to hear one of their amplifiers went from a hater to a Fan in a hurry I have owned and repaired so many amplifiers I lost track not many hold a candle to my custom upgraded c270s and my upgraded c370 I would part with many of my amps and have sold some but these 3 I would not sell its beyond money the Quality of the output is among the best I have heard not many amps can best these when they are properly rebuilt with the right parts I also have mundorfs as input coupling caps and I can say that was biggest single improvement that was so noticeable the sheer power and dynamic sound from these is impressive that and a fast slew rate to keep it accurate what's not to like about them they can drive a pair of bookshelf speakers to the power hungry Maggie's and still maintain great sound Nice Work Thank You for Sharing your experience and thank you to all that helped out I love to see people sharing their time and talent THE WORLD NEEDS MORE OF THIS
Did you do the alignment procedures in the service manual? I'm finishing a rebuild of my c372 now. I have gotten through alignment A and B without issue, but attempting alignment C I'm measuring 70V between TP701 and TP702 instead of the 50-100mV specified and I can't imagine what I've possibly done wrong!