NAD 3150 Repair experience? advice needed - diyAudio
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 27th August 2010, 02:40 AM   #1
diyAudio Member
 
Join Date: Jun 2002
Location: non
Default NAD 3150 Repair experience? advice needed

Does anyone have experience in the NAD 3150 repairs?

Someone brought me one of these to fix, the protection light is solid.

Found the left channel putting -46V DC on the outputs.

So, i did a quick static diode check of the outputs, drivers and etc.. and they all appear to be fine.

Found the schematic, and did some quick voltage measurements. the bases of both outputs have -46V on them. both bases of the driver transistors have -46 on them as well.

the -46VDC follows all the way back up to the heatsinked Q607 emitter lead. where it reads -46.5VDC

the base reads -46.7vdc. while its collector reads 51.8VDC POSITIVE voltage. Q605 looks to be darlington paired to the Q607 driver.

the base of Q605 reads 51.2vdc (varies depending on when i decide to turn the power on, but not by much).

Base of Q601 reads 51.4vdc and emitter reads 51.9vdc. the emitter is tied to the collector of the pre-amp transistor Q603 and the darlington configured driver, which was 51.2vdc.

the base of Q603 has the audio signal via scope. the emitter lead reads -2.7vdc and has NO signal. the good channel, i have a signal here at the emitter being the same signal at the base. unfortunately, this isnt the case in the bad channel.

So i removed Q601, Q605, and Q603 to be tested externally on DMM diode check. they are all fine, no reverse leakage, or cross conductance leakage between C-E.

Did an hFE test, the beta varied betwee 150 to 215 on the transistors.

Q607 and Q613, Q611 driver transistors statically checked ok out of circuit as well. but i could NOT check the hFE beta because it wouldnt physically fit in the meter's transistor socket.

I checked all the resistors and diodes inside the channel as well, and they all appear to be right on target. no opens, or out of tolerance resistors. pots are OK too.

I have never seen this type of amp circuit before. its awkward. im used to the differential style power amplifiers. this one is "different". But from looking at it, you would think that Q607 has to conduct to be able to "balance" the output, as Q607 appears to be the only way for positive voltage to get to the output/driver section. however the output/driver section seem to have full negative voltage. with no positive reinforcement.

Any ideas? It has me totally stumped, unless something is breaking down on full voltage.
  Reply With Quote
Old 27th August 2010, 01:07 PM   #2
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
that might be an option some transistors may check fine outside and brake down under voltage

start playing around transistors Q605 Q607 that is easy to replace or interchange from channel to chanel

double verify that rail voltage is proper ( since more than one exists )

regards sakis
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  Reply With Quote
Old 14th September 2010, 04:54 AM   #3
diyAudio Member
 
Join Date: Jun 2002
Location: non
i managed to fix it... the cap was shorted right off the emitter of the input transistor. and it took out a resistor in the bias circuit.

replaced both, amp played perfect...
  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 2150/3150 Schematic + advice steve_aus Solid State 1 22nd November 2011 07:15 PM
NAD 3150 Service Manual fandersen Solid State 3 20th April 2010 05:04 PM
NAD 3150 repair nukaidee Solid State 4 1st September 2009 05:07 PM
NAD 2200 REPAIR PartS Needed? erdebear Solid State 6 5th January 2005 08:59 PM


New To Site? Need Help?

All times are GMT. The time now is 07:37 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