Hi i have a85 amp when switced on says dc offset check conection ? then it turns off

GET THE USER MANUAL OR SERVICE MANUAL
AND SEE THAT THAT MEANS.
IT CAN BE,
12VDC TO THE (POWER) IS BAD 12VDC AND GROUND
OR (seems to me NOT POWER)

CAN mean one of speakers failing like this.(this)
1: shorted speaker, (CALLED VOICE COIL SHORTS
2: shorted speaker WIRES, to shorted to car body ground.
3 using wrong speaker if 2ohms is not allowed but 4-8ohms is allowed. or putting 2x 4 ohm speakers in parallel fails. as it will;./
4: amp is bad.(in the head end)


page 62 in your manual states

If the power is not turned on ("Miswiring DC Offset
Error", "Warning DC Offset Error" is displayed),
the speaker wire may have a short circuit or
have touched the chassis of the vehicle and the
protection function may have been activated.
Therefore, the speaker wire should be checked

THE REAL MEANING, (ME TOLD) IS ONE OF THE SPEAKER PRESENTS A OVERLOAD TO ANY AMP OUTPUT CHANNEL.
TO FIND THISONE MUST DISCONNECT SPEAKERS TO FIND IT.
YES SPEAKERS AND WIRES CAN SHORT.
A TECH EVEN TRIES TEST SPEAKER 1 AT TIME TO PROVE THIS.
IF ALL TESTS FAIL THE AMP IS BAD.

Check the DC off set on all of your channels. There is a good chance the one is drifting. If you find a chanel where the DC Offset is drifting (+) check for a leaky cap C113 on that channels negetive feedback circuit.

CONECT THE SPEAKER WIRE PROPERLY

you don't want to do this( bypass the protection0
that d.c. output will burn the coils in your speakers with out making a sound!! you have a biasing problem
or like you said a d.c. offset problem it is best to work on this problem with out a load on the amp, this will allow you to trace back where the trouble is starting at. caps will cause this sort of problem but leaky transistors can also do this, even diodes.
this will require an experienced trouble-shooter.

I had the same problem. The solution to me was presoldering transistor Q708. http://www.flickr.com/photos/37147023@N03/3511227679/?edited=1

Hi there

You have a DC offset condition occurring on the speaker output of the amp. This usually means that some components have blown in the output stages. Be careful turning the amp on when this is happening, if the cones of you speakers are blowing out and stay out... then they may be damaged if left in this condition too long(more than a second!!) You will need to take the amp to a serviceguy... most of these sorts of repairs need expert attention.

robotek

Hi there

Firstly, check for conductive hold down glue about the output stages. This can cause the problem you have. Or there may be a failing component somewhere in the output stage of that channel. Check for leaky transistors,diodes an capacitors. You will need to remove semiconductors to check for leakage, If you dont have alot of experience faultfinding amplifier power stages, I suggest you take it to a NAD authorised service center.

regards
Graeme

you have real problem in safety contol circuit which shut down the unit to protect the amplifier from damage

hi first disconnect all spks, then turn on the amp. if amp power lite stays on bright then proceed to connect one speaker or sub to the amp. if the amp lite dims during any spk connections then it may be that the spk is faulty or there is a DC voltage (dc offset) emitting thru that particular channel. also check all spk impedance before reconnecting them to the amp. cheers.

First check the outputs at the output fets/transistors for any DC voltage. Reference your voltmeter to the speaker - terminal. If there is ANY DC offset, the amp is shutting down the outputs to protect your speakers from DC. Is the power supply + and - 47 volts? If only one supply is there That is your problem because the supplies should be symmetrical. Also look for any wiring problems from the amp to your speakers... any shorts? Try disconnecting all your speakers to totally eliminate any speaker problem and see if the relays still click. You should hear only ONE click when you first turn the amp on (delay of about 2-5 seconds). If they keep clicking the amp outputs are next. Also, is there any indication on the front panel of what is failing?