NAD 304 Repairs

First post here.

I have a NAD 304 that i use for music while i try and finnish an amp based on a gainclone design. I turned this on yesterday to find the light was staying on red, and a smell of burning comming from it.

Searches have shown me that Some resistors should be changed, specificly R333 and R334 to 1 Watt. I have checked the resistors and they seem fine, but am about to change them anyway as i have some spare 1 watt resistors lying around.

are there any other idea's as to what is causing this - has anyone else experianced problems like this and it not been caused by the Resistors?

Thanks
 

Matthewong

Member
2005-06-09 5:10 pm
KL
I'm not able to help you since you only give me very little detail. But I can tell you that your NAD 304 protected mostly some components malfunction or spoiled. You better check that whether the transistors is still in good condition or not, then check v+ and v- voltage.
 
Thanks for your help so far, if there is any infomation you need please just ask - i will try to help as much as i can.

I have no idea what part of the circuit is damaged, i would assume it is not the powersupply or the LED would not light up at all. But other then that i have no idea.

I noticed a Fuse has slipped partly out of it's holder, as the amp worked last time it was on, could the damage be from the amp being dropped, i am guessing i should try re soldering all the joints?

Leolabs: The resistors are located neer the main transistors and heatsink. There are also a second pair that seem to be part of the pre amp which are supposed to be replaced if they are not 1 Watt items, i have checked both and they are the correct values.
 

WhyZed

Member
2006-06-27 8:29 pm
I am also having this problem of the power lamp will not turn from red to green.

I have checked supply voltages and they are there.

The 2 tall heat sinks on power board (behind the volume dial) are smoking hot and are sitting at 244vdc.

All the other heat sinks are cold.

Has anyone found the cure to this problem?
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi WhyZed,
You can't assume the problems are the same.

Can you make some voltage measurements in the amplifier section?
The 2 tall heat sinks on power board (behind the volume dial) are smoking hot and are sitting at 244vdc.
Can you read the part designator off the PCB so we can see what part it is. I don't think we are running 244 VDC in this unit anywhere.

-Chris
 

WhyZed

Member
2006-06-27 8:29 pm
Thank you for the reply Chris.

The original post seemed very “up my alley” so I chose this one to reopen. You are very correct tho, these problems may look the same but have totally different causes. It appears that the ones who post the problems like I’m having, find the solution then never post the answers for others…

My multi meter hit the floor and was suspect so I borrowed another. Sure enough, it is broken.

All fuses are good.
The ACV out of the transformer orange/violet is 75 common 75, black/grey 56 common 56.
The ACV entering the bridge rectifier [D805] is 58. DCV exiting is 78.

I remeasured between the heat sinks [Q901] & [Q905] reading 145.5vdc. I got a wee shock from them yesterday thus the voltage check. Yesterdays voltage of 244 was with defective voltmeter.

Heat sink [Q901] -72.
Heat sink [Q904] +72
Heat sink [Q906] -48.7
Heat sink [Q905] 0

Heat sink [Q905] +38.3
Heat sink [Q905] +38.3

I downloaded the manual but it is very small and blurry, I can’t read it very well.

Are there any other points on the board you would like me to check?
 

WhyZed

Member
2006-06-27 8:29 pm
WhyZed said:


Heat sink [Q901] -72.
Heat sink [Q904] +72
Heat sink [Q906] -48.7
Heat sink [Q905] 0

Heat sink [Q905] +38.3
Heat sink [Q905] +38.3


There doesn’t appear to be any mica washer between the heat sinks & Q’s 901,904,905,906. OR Q327, 328

COPY PASTE ERROR…

Heat sink [Q901] -72.
Heat sink [Q904] +72
Heat sink [Q906] -48.7
Heat sink [Q905] 0

Heat sink [Q327] +38.3
Heat sink [Q328] +38.3

thoughts on the zero volts at Q905.