always use chassis for neg lead it sounds like you are reading high rail voltage for power drive circuit i dont have schematic in front of me but i remember i did similar just measure the output from trimpot and use chassis for other and you will get proper reading if you truly had 70 volts it would go into protection right away dont be so hard on yourself you didnt do anything wrong just measured from wrong point the manuals are filled with errors thats why you do 1 at a time
I had the same measurement and it was R710 that was burnt. After changing it I was able to adjust it to -75mv
Hi diyAudio Wizards 
Hope I'm not too late to the party?
Inspired by this thread I have taken my NAD C370 apart.
I bought this amp from new back in 199? and it has been with me since - some of the time in my secondary setup.
Twenty-some years back it needed service and got some new caps.
I feel like bringing this trusty old amp up to its former glory - and maybe beyond...
But... I have some questions I hope You can answer - but first some photos of the Main Board:
The caps in areas 1 and 2 were changed during the service.
I'm not sure about the caps in areas 3 and 4?
This is this values of the caps in the 4 areas:
Well anyway. Since all of the caps are 20+ years old, would You change all the caps (also those "new" 105°C caps)? I have no brownish areas on any of the board and it working as it should - except, I remember it to sound better than it does now.
I intent to do something like SpejsMan did and what Quirkaudio has done: https://quirkaudio.com/?p=1123
The two small vertical boards are the LineIn modules (there are two more like them on the Tone Control Board - the Pre-amp modules).
These vertical boards live inside these small black houses:
At first I thought it was some magic NAD components, but thanks to Quirkaudios site I learned the truth...
I'm thinking of letting them out of their house and give them some sort of cooling plate - BUT - is these houses for shilding? They are made of aluminium.
Finally: Thanks for this thread - lots of great info. It has inspired me to dip my toes in this diyHiFi stuff - hope it turns out well
/Nik
Hope I'm not too late to the party?
Inspired by this thread I have taken my NAD C370 apart.
I bought this amp from new back in 199? and it has been with me since - some of the time in my secondary setup.
Twenty-some years back it needed service and got some new caps.
I feel like bringing this trusty old amp up to its former glory - and maybe beyond...
But... I have some questions I hope You can answer - but first some photos of the Main Board:
The caps in areas 1 and 2 were changed during the service.
I'm not sure about the caps in areas 3 and 4?
This is this values of the caps in the 4 areas:
Well anyway. Since all of the caps are 20+ years old, would You change all the caps (also those "new" 105°C caps)? I have no brownish areas on any of the board and it working as it should - except, I remember it to sound better than it does now.
I intent to do something like SpejsMan did and what Quirkaudio has done: https://quirkaudio.com/?p=1123
The two small vertical boards are the LineIn modules (there are two more like them on the Tone Control Board - the Pre-amp modules).
These vertical boards live inside these small black houses:
At first I thought it was some magic NAD components, but thanks to Quirkaudios site I learned the truth...
I'm thinking of letting them out of their house and give them some sort of cooling plate - BUT - is these houses for shilding? They are made of aluminium.
Finally: Thanks for this thread - lots of great info. It has inspired me to dip my toes in this diyHiFi stuff - hope it turns out well
/Nik
What makes you think it is underperforming?
In other words - knowledge is light, ignorance is bliss, have you measured it in any way (RMAA, REW, ...)?
The capacitors in red quadrants on the photos would be the last ones I would replace...
Hi Madis64.
Thank You very much for your responce!
No, no light - only bliss ;-)
I have neither instruments or knowledge to measure the amp... I'm totally new to this.
I'm surprised that the caps in square 2 would be the last to replace - it seems to me that it's been done to all the C370s I have seen rebuild.... but maybe it because a flaw in the design of this amp - don't know.
Thank You very much for your responce!
No, no light - only bliss ;-)
I have neither instruments or knowledge to measure the amp... I'm totally new to this.
I'm surprised that the caps in square 2 would be the last to replace - it seems to me that it's been done to all the C370s I have seen rebuild.... but maybe it because a flaw in the design of this amp - don't know.
A soundcard an a pot (or two) is what you need to start up.
They are big and shiny and they definitely persuade the amp owner to pay the "maintenance" bill. But they are the power rail capacitors - bigger problems (and effort) are usually in the signal path.
Probably glue. If it covers any nearby leads of other components then its should be removed - its effect is usually corrosive.
Regarding stamping on top of the capacitors - I have never looked at that, usually the manufacturing time of the device gives you a clue about how old the components can be.
A soundcard I have - and also some pots. But don't know what to do with them in this case. I really don't expect you to teach me this basic stuff - I should read up on it
Yes, I have learned that it is the caps in the signal path, that should be my focus.
I think i have bought into the idea that all caps "get tired" after 3 decades of service - this is maybe not the truth?
Yes, these big caps are the first that meets the eyes - I get your point.
I you have the time - do you think this looks like the right way to go? https://quirkaudio.com/?p=1123
You could start with this thread - if my memory serves me correct its content should be "educational"But don't know what to do with them in this case. I really don't expect you to teach me this basic stuff - I should read up on it
https://www.diyaudio.com/community/threads/aiwa-aa-8300-restoration-ideas.396261/
BUT.... I really appreciate you input! Thank your
I think I will take one step back and do the alignment procedure for this amp, read up on this stuff, listen some more and maybe find out about if it is possible to measure anything without investing in a ton of instruments. BEFORE ordering a lot of caps.
/Nik
"Truth is somewhere out there" - my personal practice shows that I usually do not replace the "big ones" unless the device is built in 70-ies.
The smallest ones may fail in a decade - especially if a "well known manufacturer" has decided to resort to capacitors from "Asian suppliers that nobody knows"...
Sorry Madis64 - but I am too damn ignorant to catch your drift...
Is this for feeding the output of the amp into a PC and that way do some sort of analyses?
If it is a soundcard I have one, but without any inputs - just to feed my amp from the computer (I wrote so in a former post, but because I'm new to this forum, my posts has to get approved by the modifiers first and may come a bit late):
Correct, you feed the measurement signal from the soundcard to the amplifier line input and software (RMAA, REW, etc) captures the output of the amplifier via the same soundcard.
Your first soundcard has to be a cheap one (like the 202 in Thomann link) because you will most probably fry it during your first attempts - input stage of the soundcard is not designed to handle e.g. 30...50V AC from speaker terminals (been there, done that).
Measurement signal is usually generated by the measuring software but you can also feed e.g. 1kHz and capture the amplifier output to either a file or a spectrum analyzer software.
Pots are needed in both lines to adjust signal levels.