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Old 8th February 2004, 09:36 AM   #1
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Default Need Help Fixing an old NAD 304

Hiyee,
I recently got this one off the junk yard for free...it's pretty old...about 8 years...and has a power-on problem...the soft-clip switch works...and when power is applied...the LED changes from nothing to red...it's suppossed to go to green after that but it doesn't...I've tried measuring the rails...seems to be fine...the one thing bugging me is the phono section...the preamp there uses 50-0-50...meaning a total of 100V+ for just the phono section...which is even higher than the power-amp section...is that really necessary?? There is a little relay at the top corner...but it doesn't seem to be engaging or disengaging...I'm also looking for a schematic...does anyone has one...I'm kinda like working "blind" without a schematic...I'll get my new Antex Tip and re-do all the joiunts tommorrow and report back...I guess it might be as easy as a solder problem...but maybe u guys have some ips and suggestions that I might like to know...yeah...and please dun offer a suggestion to convert it to a GC...hehe...thanks in advance. I'll also look into posting pics later...have to go borrow a digicam...mine doesn't do macros...
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Old 8th February 2004, 01:27 PM   #2
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Hi li,
Check R333, R334 both 47k/1W. This tip is from a 403 but might apply to your 304 as well.

/Hugo
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Old 8th February 2004, 02:17 PM   #3
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333 is a diode on mine...I'm gonna check all the 1watters...since u gave me tt tip...so do I have to check every part here...394 and 393 happen to be 1Watters as well...guess it'll be a long dae before I manage to fix it...what seems to kill this kinda amps?? All the fuses are intact and orginal...a few lose joints...gotta get a new tip first...stupid tips always seem to fail when u really need em...gotta stock on a few spares...
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Old 8th February 2004, 02:54 PM   #4
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Quote:
Originally posted by li_gangyi
333 is a diode on mine...
Li,
I wasn't clear enough; the original R's are probably 1/2W and should be replaced by 1W.
The exact position could be wrong also, sorry, that's the only info I've got.
However, it is very likely that this resistor(s) are the cause of your problem. Checking them all is usually not that big of a problem. Get one eye on a good DMM, the color code on the other eye and check one by one; usually such resistors are plain open so you will see your DMM measure Mega ohm's on the faulty one even without taking it out of the circuit and mostly a rather correct value on the good ones.

Iím sure youíll find the problem.

/Hugo
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Old 9th February 2004, 09:22 AM   #5
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Yeah...I'm checking all of em out of the board...just to be safe...I just got my new tip...the 1/2 watters eh...I'll look at them carefully...can this be a semi-conductor problem??
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Old 9th February 2004, 09:44 AM   #6
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Sure, as I only have that tip on two different NAD's where the symptoms are exactly what you describe I thought passing it was the right thing to do.
There is also mentioned that two resistors in the PSU should be checked together with bad solder joints.
Can you measure DC at the output(s) before the relay?

/Hugo
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Old 9th February 2004, 10:27 AM   #7
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ehh I'll first test the whole thingy before I do a second power up...afriad I might fry something...I'll measure later...
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Old 11th February 2004, 02:51 PM   #8
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I just practically resoldered the whole board...nope..still no go...I measured the outputs with reference to ground...there's no voltage present...but the relay just doesn't click...and I'm still not getting any power to the relay even...can anyone tell me how the relay is hooked up...I.E where the coil pins are?? Thanks in advvance...
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Old 11th February 2004, 03:40 PM   #9
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You can measure the coil pins with an ohmmeter. Sometimes there is a diode parallel with the coil. Are you sure it's the output relay? If it is, it's rather unlikely it is broken. Sometimes there's a (bipolar) cap near the relay. Check that as well.

Looks like you will need a schematic.
Found a link for you: http://www.electronicsrepair.net/rec31.shtml

/Hugo
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Old 11th February 2004, 09:24 PM   #10
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argh~!!!...I hate tt thingy...needs to pay by credit card...and I dun have one~!!! What can I do next??
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