AU 20,000 No Power

sansuilove

Active Member
Hello
Few weeks ago, noises started coming from the left channel of the amplifier .
Took it to a local tech and few days after he contacted me claiming he 'found' a small spring at the power amp boards that made a big mess and unit does not power on any more.
After arguments with him that I took him a working unit I decided to take the amplifier back to me.
The fuse on the back (6A -220/240 voltage)
Was blown.
Replaced with a new one and fuse blew again.
Took his advice and removed ALL 12 output transistors .
Tried to turn it on again and nothing - no power
Checked all fuses on the protection board and all are OK.
What should I be looking for?
Would appreciate your help.
 
What outputs did you use?
Is the power switch working?
I'll test the transformer and the rectifiers first, and test voltages from there with the schematics on hand.
Hang on, someone with more experience will chime in.
 
Didn't use any new transistors - just pulled the originals out.
as far as I know it works but worth checking
Your answer is pretty contributing And gives me a way of working
Thanks
 
as far as I know it works but worth checking
Way more than that, it deserves a nice restoration :thumbsup:.
Sadly I've never have the opportunity to get one, so I don't have experience with that unit.
How are your skills regarding electronics? Can you read schematics?
Do you have the service manual?
Check f-2511 and lets wait for more help.
 
claiming he 'found' a small spring at the power amp boards
What does this mean?

As you have pulled all the output transistors - have you tested them with a meter? Testing instructions are at various places on this site.

Your immediate problem appears to be a loss of power however. No click? No indicator light?

I agree that you need to start by finding the service manual and testing that you are getting firstly, primary power to the transformer and then secondary power from the transformer. Are you confident doing this, as you will be dealing with high voltages. Plus this amp is not the most straightforward to work on.
 
I have good electronic skills and ability to read manuals and schematics .
I recapped the amp 3 years ago but power switch didn't get any treatment.
 
What does this mean?

As you have pulled all the output transistors - have you tested them with a meter? Testing instructions are at various places on this site.

Your immediate problem appears to be a loss of power however. No click? No indicator light?

I agree that you need to start by finding the service manual and testing that you are getting firstly, primary power to the transformer and then secondary power from the transformer. Are you confident doing this, as you will be dealing with high voltages. Plus this amp is not the most straightforward to work on.


He contacted me saying that he found a spring came from somewhere and touched the power amp boards or driver boards and made this mess. What I think is he just made a mistake and fried something and now trying to wash his hands off - credibility issue.

No click - no protection light
Will check the power at transformer and let you know guys
Thanks
 
There are several good threads here in the Sansui forum on the AU-20000.
An absolutely excellent one by akr kale.
Check it out!
I also had the honor of restoring one of these fine amps last fall.

Bob
 
Download the service manual from HiFiengine.com.
First thing - with the power tranisistors removed or the power removed from them check the power regulator board for correct voltages.
In my experience the power regulator board gets very hot which seriously degrades the solder joints.
 
Output transistors are all out of amp.
Pulled all connectors out of F-2511 protection amp and tried to get some readings out of the transformer - couldn't find my way very well .. I get only 60VAC out of the yellow wires (9+11)
How do I identify the primaries from the secondary?
I'm starting to suspect the transformer is bad..which is the worst scenario I can think of :(
 
Do you understand 'soft start' circuits? - check the soft start resistor(s).
I'm starting to suspect the transformer is bad..which is the worst scenario I can think of
I would also worry about this, there has been some chat here on AK about the absence of main rail fuses in this model, and if there is a serious short circuit on the main rails, (as appears to be the case here), what this could mean for the safety of the transformer - made vulnerable by this omission.

Read Troubleshooting section 3.1, subsection 1, in the service manual.
 
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Disconnect the transformer leads from the circuit board.
With dmm set to measure ac volts---
Measure each wire to ground, not to each other btw.
Blue wires 46vac
goes to pins 5 and 6
Yellow wires 60vac
goes to pins 9 and 11
White wire 5.7vac
goes to pin 14 and 15
Red wire 22vac
goes to pin 12 and 13
This will indicate transformer condition.
If you are using a dim bulb tester (recommended) there will be about a 10% voltage drop from these readings.
 
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Ok I located Black probe at speaker ground terminal
Readings :

Yellow #1 - 27Vac
Yellow #2 - 27Vac
Brown #3 - 20Vac
Blue #5/6 - 0
Green #10 - 2Vac
Red #12/13 - 5Vac
White #14/15 - 9Vac
Yellow #9 - 1.9Vac
Yellow #11 - 1.9Vac

Measured R01+R02 on f-2511 :
R01 - 0.9M !!!
R02 - 3.9 ohm
It made me a bit confused because on the resistor it says 3.9K but service manual says 3.9 ohm
Ordered a new pair already
 
:(I can't express how angry and upset I am if it's true
Could be that the power switch isn't making a full contact or has some kind of malfunction?
Any thermal inner fuse?
 
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Possibly, be very carefull here working with mains voltage. If you have a switched outlet in the rear of the unit measure ac across the two slots when power is applied.
 
:(I can't express how angry and upset I am if it's true
Could be that the power switch isn't making a full contact or has some kind of malfunction?
Any thermal inner fuse?
Let's wait what the others say, but if we compare what Overundr1 voltages say... Did you did the trobleshooting chart on page 4 of the service manual? Maybe something else is faulty in addition to resistors.

Capture.PNG
 
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