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Old 12th July 2015, 12:32 PM   #1
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Default nad 701

hi all im am new to the forum and need some advice with my nad 701 amp, i bought it two weeks ago and it worked fine when all plugged in, i turned it back on 2 days later and very low distorted sound and it switched into a protection mode, i have had a read around and replaced the four big metal transistors mj2955 & 2n3055 and acouple of others b649a &d669a as they were getting hot and its still the same but now the sound is louder but still distorted and the amp now stays on, do i need to add the resistors which people say to do in a thread on here and could someone please say what resistors i need and where to solder them thanks for any help, also does this amp have mute transistors and how can I locate them to test thanks in advance

Last edited by sirius1967; 12th July 2015 at 08:58 PM. Reason: Adding a question
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Old 19th July 2015, 04:18 PM   #2
M Gregg is offline M Gregg  England
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Quote:
Originally Posted by sirius1967 View Post
Hi all I am new to the forum and need some advice with my NAD 701 amp.

I bought it two weeks ago and it worked fine when all plugged in, i turned it back on 2 days later and very low distorted sound and it switched into a protection mode.

I have had a read around and replaced the four big metal transistors mj2955 & 2n3055 and acouple of others b649a &d669a as they were getting hot and its still the same but now the sound is louder but still distorted and the amp now stays on.

Do i need to add the resistors which people say to do in a thread on here and could someone please say what resistors i need and where to solder them thanks for any help, also does this amp have mute transistors and how can I locate them to test thanks in advance
Do you have a link to the Schematic?

That may get you more help.

Regards
M. Gregg
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Old 19th July 2015, 04:56 PM   #3
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yes i have the shematic 701 i found it on here, i have used it to order exact replacement parts, im still waiting for some transistors to get here before i can go any further, up to now i have changed all the .1uf caps 180ohm resistors 100ohm resistors mj2955 & 2n3055 and still need to change 4amp fuses, can i replace the 6800 caps with 10,000 to improve sound ?, thanks for your reply

Last edited by sirius1967; 19th July 2015 at 04:59 PM.
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Old 19th July 2015, 05:15 PM   #4
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If this amp is as old as I think it is, and if it sat un-used for a long period, any electrolytic or tantalum caps could be bad. In the NAD preamp I have, the push button switches got dirty over time and became intermittant, causing a very loud hum...
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Old 19th July 2015, 05:16 PM   #5
Mooly is offline Mooly  United Kingdom
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Where are you up to with this ? In post #1 you mention the sound was louder ! after replacing transistors......

Does it all power up OK now or is it still running hot. The first clues will be in a few vital voltage measurements around the output stage.
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Old 19th July 2015, 05:47 PM   #6
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Hi sorry, all but one fuse is blown, after testing transistors q415,q417,q418,q416,q411,q409q413 (split in two) q414,q410,q412, q407 and 408 around half was damaged, resistor 453 was fried other resistors seem ok ? Tested loads out of circuit, l am just waiting for some parts to arrive then I will change them, thanks for the replies
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Old 19th July 2015, 05:50 PM   #7
Mooly is offline Mooly  United Kingdom
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When you have replaced the faulty parts make sure you power this up using a 'bulb tester', which goes a long way to preventing damage should any further faults be present.
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Old 19th July 2015, 06:07 PM   #8
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Default NAD 701 Schematic

Left main amp part of the schematic - makes it easier to follow. If anyone needs it, the full service manual is on elektrotanya.com

NAD 701.JPG
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Old 19th July 2015, 06:29 PM   #9
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I no what the symbols mean, diode capacitor ect my problem is the actual board layout is so different I get lost with it so I have been ordering parts and changing them, all the .1uf caps are swollen so I've changed them along with a few other bits for now, so till I have them all I'm stuck, thanks for your reply
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Old 19th July 2015, 07:24 PM   #10
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Can you get some good sharp photos of the innards of the amp?

If you want some good tutorials check the links below.

John
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