NAD 3130 blowing fuses

[danbatts]

Hi there - I'm hoping someone may be able to help.
I've got a NAD 3130 integrated amp that I've been using for 20 years without any trouble, until last week. Left the amp on while I connected different speakers ( I know ! ), and blew a couple of fuses - F3 and F4, both 4 amps. Changed fuses 3 times now and they blow immediately on powering up the amp, even with volume turned right down, no sound input and speaker switch turned to off ( and speakers wired properly now ). F1 and F2 aren't blowing though... There's 4 fuses : F1 and F2 are 1 amp. There is some sound but very low level and totally distorted. So, maybe the output transistors are blown/dead ? And if so would that be all 4 ? There's 4 of them - Is it 2 for each set of speakers ? The transistors are 2 X 2N3055 and 2 X MJ2955...
Would it be relatively straightforward to replace them ? Costly ?
Any help anyone can offer will be very much appreciated - I'm using my girlfriends cheap amp in the meantime... unpleasant.
Many thanks,
Dan

[jblmar]

Sorry, but disconnecting/connecting speakers with the power on will destory transistors. You need to weed out the defective parts and replace them. Shorted transistors and diodes will blow fuses.

Ron

[Bigred]

Originally posted by danbatts
Left the amp on while I connected different speakers ( I know ! ), and blew a couple of fuses - F3 and F4, both 4 amps. Changed fuses 3 times now and they blow immediately on powering up the amp

Never change a fuse without atleast determining (providing its glass) if it was a"light" or "hard" blow (hard blow=glass coated black or silvery... in this case DO NOT REPLACE or run the risk of FURTHER damage) And ESPECIALLY don't replace a fuse 3 times expecting a different result.

So, maybe the output transistors are blown/dead ? And if so would that be all 4 ? There's 4 of them - Is it 2 for each set of speakers ?

No not necessarily any or all 4 have been damaged. If they are, damage may not be limited to the outputs. Yes it will be a complimentary pair per channel. It sounds like you damaged both channels so if you find only 1 output trans per channel damaged, I'd replace the pair anyways. I "think" the drivers are 2SD669 and 2SB649 (check those also along with shorted diodes, open resistors... I'd bet you have caused more damage due to 3X blown fuse replacement)

Would it be relatively straightforward to replace them ? Costly ?

Do you have a DMM?, soldering skills? any electronic background and know precautions to take like power supply cap discharging.... using a variac or dim bulb tester upon powering up? Are you overwhelmed yet? Maybe a qualified repair tech is in order. Costly?.... no the outputs themselves are cheap.

[timbert]

Search for a thread I started a month ago "NAD 701 receiver"