Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 1st February 2013, 08:49 AM   #1
optilab is offline optilab  France
diyAudio Member
 
Join Date: Jan 2013
Default NAD 3020e fried R451 R437 resistor

Hello friends,
I have a problem with my NAD 3020e.
The resistor marked r451 and r437 are fried.
The fuse are still in good condition.
I suspect Q409 or Q407 ?

What do you think ?
Also do you think it is a good thing to change all the capacitors to start a new life with this amplifier?
Thank you for any help.
Pablo

Click the image to open in full size.Click the image to open in full size.
  Reply With Quote
Old 1st February 2013, 09:39 AM   #2
diyAudio Member
 
Join Date: Apr 2010
Location: Coffs Harbour, on the east coast
Hi Optilab and welcome, if this is your first post.
Why not check the voltages marked on the schematic in the area from Q405 to the right side first?
You can mark up the schematic or type as text with a clear indication of the point referred to.
That will help others understand what is wrong much easier.
__________________
regards
  Reply With Quote
Old 1st February 2013, 09:39 AM   #3
diyAudio Member
 
Join Date: Jul 2003
Location: Dona paula, Goa
First of all, do not mix repairs with a mod. Repair it first.

You should check the power transistors and the drivers Q 411,413,415,417.

Gajanan Phadte
  Reply With Quote
Old 1st February 2013, 06:52 PM   #4
optilab is offline optilab  France
diyAudio Member
 
Join Date: Jan 2013
Hello guys,
thank you for helping.
I can power up the amp to check voltage or should I desolder the transistor and check them with my multimeter?
I heard about putting a light bulb between the amp and the socket?
Anyone could tell me more?
Thank you.
Regards.
  Reply With Quote
Old 1st February 2013, 07:01 PM   #5
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
A bulb is a great safety measure to avoid mishaps. Use a 100watt filament bulb.

Both voltage checks and static checks should be used to try and determine what has failed. The two driver transistors (the 2SB649 and 2SD669 would be prime suspects for failing intermitently and could be the source of the original failure).

Its always nice to find the fault but sometimes its more cost effective and certain to replace any suspect parts rather then find the amp appears fixed only for the same problem to surface again later. The cost of replacement is minimal and there are more up to date and easily available replacements such as the MJE340 and MJE350 for the drivers.

Good to learn though... get it powered up and get measuring
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 1st February 2013, 07:06 PM   #6
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Nearly forgot... for initial working on and testing of the amplifier you can apply a short (solder a piece of wire) between collector and emitter of the vbe multiplier (is it Q409 ? can't make it out clearly... the one in the middle with the square around it). The amp will work and function normally like this (apart from slight crossover distortion ) and it will force the output stage to run at zero bias current (assuming no other problems exist).

And don't connect any speakers to the amp until its fixed. A DC offset could destroy them.
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 1st February 2013, 07:38 PM   #7
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
If you replace the transistors, you will need to make a modification. The original parts work OK without emitter resistors, and so they are not in the design. However, modern parts will not, and you will need to add 0.22R emitter resistors for stability.

I'd say the damage has been caused by failure of at least one output device, and it's driver transistor
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
NAD 3020e recapping adventure Rohanv Solid State 14 25th October 2013 06:07 AM
NAD 3020e low volume and distortion... fried 68R resistors byron99 Solid State 6 7th May 2011 09:25 PM
Couple of Nad 3020e questions soupdragon Solid State 4 14th February 2010 02:02 AM
nad 3020e bull041161 Solid State 18 29th March 2009 12:38 AM
Problems with NAD 3020e pho_boi Solid State 3 1st February 2006 09:02 AM


New To Site? Need Help?

All times are GMT. The time now is 11:16 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2