Question about Audio Players & Recorders
Hi, My NAD Electronics 7020e amp keeps blowing one of the 4A internal fuses on power up. I am looking for a short but cannot find it. The power amps check good, the rectifier diodes seem okay and I checked most all transistors and diodes and cannot find anything. Any ideas? Thanks.
Well you are on the right course. I suspect you think the problem is in the power supply and it's probably not. I think that what's gone is either a transistor (or more) or an IC amp - if it uses one - on the main power amp stage. Look at the devices on the heat sink. I think that's where you will find your shorted device.
Posted on Dec 17, 2012
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Posted on Jan 02, 2017
SOURCE: amp blows fuses
The fuses are there to protect the internals of the AMP.....
Please check that the correct fuses are installed......
if the incorrect ones are installed then a fire may develope...
There should be a manufacturers lable on the external chassis that details the fuses to use....
Fuses now days can be slow blow or fast blow....so the correct fuses must be used.....dont increase the fuse rating past the chassis panel label...but make sure they are correct...if they are correct then the amp needs a service to determine where the peak loadings to the power supply are originating from...
Some one may have installed incorrect fuses in the past...
Cheers from YUBEUT
Posted on Nov 03, 2007
SOURCE: NAD 370
Hi There is no circuit breakers inside. close to front panel on a left side under plastic cover is fuse (AGC type) . Before you change fuse look at four filter capacitors in the middle of unit!!! (close to power transformer on pcb) If they are white do not change the fuse and get unit to good service center( it must be someone who knows what they doing!!!) If the caps are different color (black ,purple) you can try to change fuse. Once again if capacitors are white do not use unit-fire hazard!!!! I'm long time service guy for NAD so trust me on this one Dariusz email@example.com
Posted on Feb 13, 2008
SOURCE: NAD C350
Take a ohm meter and measure resistance from emiter to collector should have a few kilo ohm on output transistor.
If no ohm meter available , remove output transistors from circuit.
note position of transistor . you have a NPN and a PNP for each channel.
Replace fuse and power up. If fuse blows check bridge in the power supply.
80% of the time output transistor burn and blow the fuse.
before replacing output transistors check driver transistors they probably burnt also
Posted on May 04, 2008
Thanks for the clarification. From the fuse behavior and feeding the amp into another amp (generally a no-no) it almost certainly is in the output section. If the amp used output transistors (numbered something like Axxxx/Cxxxx where xxxx=0000-9999) there will be some white three-legged low value (.47 ohm or less) resistors that are probably open. FYI the full part numbers for the transistors would be 2SA/2SC so a part marked C3281 would need a 2SC3281. B+D Enterprises (Google them) has most Japanese semiconductors and they have never sold me a fake transistor.
For more repair tips check out www.audiokarma.org
Posted on Dec 29, 2008
Fuse blowing is due to excessive current drain and the the first clue is the blown fuse itself. If the fuse blows with a flash a bang and splatters copper across the inside of the glass you have a hard blow caused by a dead short on the power supply, check for power switch flashing over internaly. Short circuit main filter capacitors. Shorted turns in power transformer primary winding. If fuse just separates check for short on output transistors C to E. Try isolating fault by disconnecting LT pos/neg supplies to output stage. Also check for partial shorts on speakers and speaker wires using an analog ohm meter on low ohms setting.
Posted on Mar 28, 2010
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