Sansui AU-555A Dead channel - 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 20th September 2012, 02:19 AM   #1
diyAudio Member
 
Join Date: Apr 2005
Location: Simcoe Ont
Default Sansui AU-555A Dead channel

I have amp with bad power in amplifier section.
I am certain it is not in the preamp stage.
I have have heard "caps" and I have heard "transistor"
I am away from home and was hoping to order parts for a weekend project.
Could somebody suggest what to replace on this amp?
I want to to order my components asap and have them waiting for me.
I'd rather solder it all in then to underestimate what I may need.
Thanks
  Reply With Quote
Old 20th September 2012, 10:59 AM   #2
diyAudio Member
 
Join Date: Apr 2010
Location: Coffs Harbour, on the east coast
This is a very old amplifier. You describe the fault(s) as 'bad power" which could refer to anything but let's assume you mean bad sound - perhaps distortion? Is it low power, lacking bass, treble etc? What sort of bad power do you mean?

In the case of old gear, capacitors eventually dry out and fail and this leads to semiconductor failure too. Faults will likely be as you already suspect but there could be collateral damage to resistors, PCB traces, connectors even. Corrosion can be a factor too so assume nothing without checking the obvious physical evidence and re-joining any connectors, if used for parts or leads.

I don't have a schematic to refer to but it will be unlikely that you will find original replacement power semis anywhere local and there is little point replacing them until the electrolytic type capacitors are replaced. When you have done this, power up with a current limiting device in the power line, such as a conventional lightbulb or variac or current limiting power suppy to prevent further damage in case other parts are taken out when the circuit operation is restored with good caps. It is easy enough to re-cap, allowing that you can use higher voltage ratings and say 50% higher capacitance ratings if necessary to obtain parts that both fit with hole spacings and the space available plus even mounting clamps if they are used. Replace them all in an old beast like this and use reasonable quality parts by Panasonic, Elna, Nippon Chemicon, Rubycon etc. Don't try to fit special grades until you find what is wrong and sort that first.

Keep us updated with progress and good luck
__________________
regards
  Reply With Quote
Old 20th September 2012, 11:34 AM   #3
RJM1 is offline RJM1  United States
diyAudio Member
 
Join Date: Jan 2010
Location: Titusville, Fl.
Schematic available here.
http://akdatabase.org/AKview/albums/...0Schematic.pdf
  Reply With Quote
Old 20th September 2012, 12:41 PM   #4
diyAudio Member
 
Join Date: Apr 2010
Location: Coffs Harbour, on the east coast
Thanks indeed, RJM1.
Like the contemporary Sansuis, it's a Quasi- complementary, single rail power source design and output is via a big cap (C819, 820). Check for DC on the +ve output connector, as a priority - it should quickly settle to zero volts via R843,4 if it is OK. Using ground as a reference point for the -ve probe, check the power supply voltage at fuses F001,2 and also measure voltage on the +ve terminal of C819,820. Take care not to short close spaced tracks or connections. It should be close to half the supply voltage and can be a very helpful indicator in isolating output stage faults.

Note that speakers and inputs should be disconnected for this test. It has a preamp disconnect even - how good is that?
__________________
regards
  Reply With Quote
Old 20th September 2012, 01:18 PM   #5
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
there you go :

vintage amplifier repair/upgrade manual
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  Reply With Quote
Old 20th September 2012, 04:57 PM   #6
diyAudio Member
 
Join Date: Apr 2005
Location: Simcoe Ont
I should have clarified that the dead channel is not completely dead but is weak and distorted.
I swapped channels VIA the jumpers and the right channel continues to be the bad one.
I was hoping there would be an easy solution like "order this, that and this".
I am thinking it is best to just replace the caps with good ones and solder in a handful of outputs.
  Reply With Quote
Old 20th September 2012, 05:23 PM   #7
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
your approach is bad ...

outputs are on-off devices either work or not

1-RTFM
2-change as many caps possible starting from the small ones on the amp section
3-clean all pots switches and trimmers in the best possible way


Additional information
Even if there was a solution like : ""change R128 and all will be fine"" then
A) usually forum members are tech guys do not like ""fast food solutions"" and see most repairs as an opportunity for a small upgrade also

B) that any way will not apply in your case since the amplifier is quite old and suffers from a number of problems eventhough only one take the amplifier down ...

As a closing argument please notice that repairs is about being methodical and follow procedure which in both you seem to fail .

Kind regards
sakis
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  Reply With Quote
Old 20th September 2012, 06:22 PM   #8
RJM1 is offline RJM1  United States
diyAudio Member
 
Join Date: Jan 2010
Location: Titusville, Fl.
I would do some more troubleshooting before you order parts. The simplest thing you could do is plug in a set of headphones and see if the distortion goes away. If it does then it means that everything is ok up to the driver transistors. Then you would have an open emitter resistor and probably a shorted output transistor (R837,839 TR809,811 in one channel R838,840, TR810,812 in the other channel. That's the first thing that I would look at since you say one channel is distorted.
You didn't say which channel was distorted so I included the location numbers for both channels.
You only have to check the distorted channel. At least you have one channel that works so you can make resistance and voltage checks between the two channels to find out where the problem is.

Last edited by RJM1; 20th September 2012 at 06:29 PM.
  Reply With Quote
Old 20th September 2012, 08:27 PM   #9
diyAudio Member
 
Join Date: Apr 2005
Location: Simcoe Ont
Yes it is didtorted even in the Headphones.
I am not sure whether the previous comment was an insult or constructive critisism.
I have no education and very little experience with this stuff. I am an automotive technician and have experience only with 12VDC circuits. I would really love to understand electronics but every time I attemp to learn it, I get overwhelmed. Does that mean I have small brain?
  Reply With Quote
Old 20th September 2012, 08:53 PM   #10
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
No it was a bit of arrogance to people that look for fast food solution and/or do not appreciate the simple help given . Please do not take this as a personal attack or an insult .
Take it as a helpful advice cause this was the real intention . To read the manual will take just a few minutes and to perform the advice given will take for an amateur a couple of days and may be 10-15 usd .

In between many people will run to your aid including me ... but please ...don't expect the amplifier to fix itself ! you have to do a few things like you ve been told so far .

Kind regards
sakis
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  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
WTB: Sansui AU-70 or AU-111 for restore (doesn't have to be working) hatrack71 Swap Meet 0 14th August 2012 11:33 AM
one chan dead on sansui au-4400 amp. dzikamai Solid State 3 17th November 2009 12:44 PM
Sansui Integrated Amp AU 919 No right channel Hanshin Solid State 1 5th April 2009 12:56 PM
Sansui AU-3900 mot on/off Solid State 18 30th May 2007 04:10 PM
Sansui Au-517&au-717 ManUtd Solid State 4 29th March 2004 01:13 AM


New To Site? Need Help?

All times are GMT. The time now is 08:53 PM.


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