Power transistors in Luxman L-430 - 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 8th May 2014, 05:03 PM   #1
diyAudio Member
 
Join Date: Apr 2014
Default Power transistors in Luxman L-430

Hi all DIY audio'ers Im new to this site, so please have a little patience with me.

I'm trying to repair a Luxman L-430 for a friend of mine. The story is as follows:
He put two 4-8 Ohms speakers on one channel (the left one) when he was doing some testing - onfortunately that didnt work out well - a lot of smoke came up the amplifier and he pulled the powercord out. I opened it up and could see a couple of fried resistors, some 1/4W, one 1/2W and two 0,22 Ohms 3W - I replaced them and continued with testing the power transistors. The 4 output transistors (2 pair of 2SA1227A and 2SC2987) were shorted, so I replaced them as well. I powered everything up and it seemed OK - so I went on an connected some music to the input - the right channel stills works fine, the left one works, but is VERY distorted/noisy when turning up the volume. I have adjusted the quiescent current according to the service manual - that did not do any difference.

I would be very happy if someone could give me some advise on how to continue the troubleshooting. I have recorded the sound, and attached it It sound OK when the volume is only a little bit turned up, but when turning it more up, it starts to sound very bad.

UPDATE: Just tried with headphones in the headphone jack - seems to be the same issue. Does that indicate an issue in the preamplifying stage?
Attached Files
File Type: zip REC.zip (457.2 KB, 46 views)

Last edited by jannsvej; 8th May 2014 at 07:59 PM. Reason: Update
  Reply With Quote
Old 15th May 2014, 07:11 PM   #2
orbanp is offline orbanp  Canada
diyAudio Member
 
Join Date: Jul 2007
Hi,

Welcome to diyAudio!

If you follow the schematics, the signals to the headphones also come from the speaker output, so chances are that the PA stage still has some problems, and it is not the preamp.
If I see in the manual correctly, the preamp and PA wiring can be crossed (the left and right channels), by using jumper cables for the signal processing terminals. In this way you can see if the distortion stays with the PA or if it goes with the preamp.

What kind of test equipment do you have?
It would be nice if you had a scope!

If you only have a DMM, start by checking the DC output level. With no input signal the DC level should not be more than 10mV or so.
Do check other DC levels in the PA stage, and compare them to the values of the other channel. You probably still have some problems in the driver stages!

Good luck, Peter
  Reply With Quote
Old 15th May 2014, 08:36 PM   #3
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
In my experience the output transistors blowing can often take out VAS and CCS and bias stages.
At least the amp runs so you can compare the two channels.

If you still get stuck then replacing the bias, VAS and CCS transistors should fix it.
If not then the problem might be further back in the LTP.
Some basic checks of transistors (even in circuit) might point to the problem.

When I am stuck I remove all transistors and check them with a DMM or transistor checker.
Then I check each discrete components value while the transistors are out.
Might even be a fried/blown resistor.
__________________
PCBCAD51 pcb design software. http://murtonpikesystems.azurewebsites.net/
  Reply With Quote
Old 16th May 2014, 05:50 AM   #4
diyAudio Member
 
Welcome's Avatar
 
Join Date: Mar 2013
Where did you get you get the new output devices? The originals in this amp are obsolete, and cannot be found anywhere. If you got new parts with the same number, they will likely be fake.
__________________
  Reply With Quote
Old 16th May 2014, 12:34 PM   #5
diyAudio Member
 
Join Date: Apr 2014
Thanks for all the answers - I will try it out when I have som sparetime again
Welcome: the originals were apparently replaced with 2SA1227 and 2SC2987, so I got them again so the channels would match. I looks like the replacement are 120W and not 100W like the originals - maybe that is why I have trouble fixing the unit :/
Kessler Electronic in Germany have the originals: 2SA1265: 2SA1265
2SC3182: 2SC3182
  Reply With Quote
Old 19th May 2014, 01:00 PM   #6
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
Quote:
Originally Posted by jannsvej View Post
Thanks for all the answers - I will try it out when I have som sparetime again
Welcome: the originals were apparently replaced with 2SA1227 and 2SC2987, so I got them again so the channels would match. I looks like the replacement are 120W and not 100W like the originals - maybe that is why I have trouble fixing the unit :/
Kessler Electronic in Germany have the originals: 2SA1265: 2SA1265
2SC3182: 2SC3182
The transistors shown in the pictures are big time fakes !! get those and you are going to have a ticking bomb in your hands ...

You should go for other combos and re adjust the bias
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  Reply With Quote
Old 19th May 2014, 02:38 PM   #7
diyAudio Member
 
Join Date: Apr 2014
Quote:
Originally Posted by east electronics View Post
The transistors shown in the pictures are big time fakes !! get those and you are going to have a ticking bomb in your hands ...

You should go for other combos and re adjust the bias
Okay, too bad How exactly do you know they are fakes?

And can anyone recommend another combo than 2SA1227A and 2SC2987 instead of the originals, 2SA1265 and 2SC3182 ?
  Reply With Quote
Old 19th May 2014, 10:25 PM   #8
llwhtt is offline llwhtt  United States
diyAudio Member
 
Join Date: Jun 2008
Location: SoCal
ON Semi MJW0281G and MJW0302G should work nicely.

Craig
  Reply With Quote
Old 20th May 2014, 10:45 AM   #9
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
Quote:
Originally Posted by llwhtt View Post
ON Semi MJW0281G and MJW0302G should work nicely.

Craig
Absolutely not !!!! drivers will not be able to drive them properly speed will be an issue and bias data will need to be modified to operate properly ...In no case these cannot be drop in replacements

There is plenty of available and original combos that will be very close to the original without any of the above problems
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  Reply With Quote
Old 20th May 2014, 11:05 AM   #10
diyAudio Member
 
Join Date: May 2008
After your replacements, the power output stage should be O.K. now.
Please check driver transistors and resistors in the driver stage.
Also transistors, resistors and diodes down stream can have failed.
Preamplifier should be O.K.
Best regards, 968driver.
  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
Luxman L-120a w blown transistors. Help needed. Jonas83 Solid State 8 16th August 2013 01:14 AM
Luxman m4000 transistors vyju Solid State 17 18th June 2012 04:14 PM
Luxman L-3 crack in speakers at power-on/off Pierre83 Solid State 2 17th January 2011 07:20 PM
Help! Luxman L-430 schematics... kesrmk Solid State 1 27th February 2009 01:55 PM
luxmAN M-117 power realys SHOT! HELP! analogue_lover Solid State 5 26th May 2006 12:25 PM


New To Site? Need Help?

All times are GMT. The time now is 02:29 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2