If yours really is a standard 3020, the area you point to has 2 small caps C417, 418 but there is no C427 in the parts list or on the schematic, that I can see. The manual says these are 47uF 25V rated electrolytic type, as identified by Avtech. You can be certain if it is also next to a group of 4 small diodes.
It looks so. Diodes (D405-D408).
This capacitor its exacly next to C422 (ceramic i think)
Thank you for the information.
The smaller regulator board has a C915,C916 which are 10uF 35V.
Can i replace them with 22uF 35V (whats the funktion of them) ?
If not, I will have to order them soon.
C915, 916 are respectively in parallel with C901,902 smoothing caps for the +/- 28V DC power supply. This is said to reduce the high frequency impedance of the large electrolytics and hence reduce noise. They are not critical values and you could fit good quality 22uF types but the lower value would be preferable.
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The problem is that NAD 3020 had 2 versions of regulator boards.
C915 and C916 (10uF 35V) were renamed and you cant find them in any service manuals.
These which you pointed for me are 2200uF x4. I am sending you picture of this board. Imgur: The magic of the Internet
According to my notes, the C427 you're referring to should be 10uF / 35V - it's indeed not in the service manual, but was in an amp I rebuilt a couple of years ago.
During the same rebuild, I also found the C915 & C916 caps on the regulator pcb - they were additional to two of the main 2200uF filter caps (also labeled C915 & C916) on the main pcb. The regulator board C915 & C916 were the same as yours: 10uF / 35V.
I'm not certain anymore where they fit in the circuit, but you should be able to easily see it from the solder side of the pcb. I just replaced all 3 with 10uF / 50V Pana FC
I have some Rubicons WXA 10uF 400V.
Do you know some disadvantages of using higher voltage capacitors (35V ->400V) ?
^ TRANSLATION:OK many thanks
In my schematic manuals, list of only electrolytic capacitors is:
1uF 16v.
806
4,7 uF 25v.
401-402-417-418
4.7uF 35v.
913-913
47uF 6.3v.
409-410-513-518-523-524-605-606-701-702
47uF 16v.
802
47uF 25v.
625-626-703-706-801
47uF 35v.
907-908-911-914
470uF 35v.
905-906
220uF 16v.
807
1000uF 6,3v.
615-616
2200uF 35v-
901-902-915-916
In my schematic manuals, list of only electrolytic capacitors is:
1uF 16v.
806
4,7 uF 25v.
401-402-417-418
4.7uF 35v.
913-913
47uF 6.3v.
409-410-513-518-523-524-605-606-701-702
47uF 16v.
802
47uF 25v.
625-626-703-706-801
47uF 35v.
907-908-911-914
470uF 35v.
905-906
220uF 16v.
807
1000uF 6,3v.
615-616
2200uF 35v-
901-902-915-916
sorry my bad english. such as 2200uF 35v. do you recommend? I add some photos of my NAD3020 series 20 do you advise me to replace all the electrolytic capacitors?
Link for photos:
Shared album - Pasquale Galasso - Google Photos
Link for photos:
Shared album - Pasquale Galasso - Google Photos
If you really like the amp and have the funds, wherewithal and time, then yes.
Go slowly (carefully) and recheck the amp eacht ime when you've completed different sections to avoid recapping and finding you've introduced a fault.
Get whichever you choose of the better brands (nichicon, ruby's panasonic etc.)
There's plenty 2200uF/35V out there, for these PSU ones go for similar diameter ones.
The slightly more important ones are the smaller values in other areas, especially directly in the audio path.