Luxman A-471-Schematic - diyAudio
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Old 21st April 2008, 02:47 PM   #1
ROVSING is offline ROVSING  Denmark
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Default Luxman A-471-Schematic

Could i be so lucky that someone here got a schematic on this amplifier, can't turn it on at all - might be somewhere in the PSU part thére is what i think is some kind of a softstart, it gets 220v ok but no voltage at the primary part of the transformator - a schematic wold be a great help or if some of you specialists could tell me what is wrong - thanks in advance...
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Old 27th October 2008, 06:48 PM   #2
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Default exactly the same problem

Hi all,

I exactly have the same problem as rovsing.
When I press the power button nothing happens (in the front panel).

If I check the power, it is ok, the 220V comes well. But nothing in he primary of the transformer.
I tried to shunt the relay in the case it was dead. Then, the power goes in the primary of the transformer but nothing happens as well.

I guess that the amplifier is under tension and may work, but the front panel is not working at all, so I can't select anything.

I gave a look to the front panel electronic card and nothing is mechanic, everything is electronic. My assumption is that the amplifier has a problem in the front panel, maybe a chip is dead.

It would greatly help if someone could provide me with the schematics of this amplifier, so that I might be able to find and maybe fix the problem. Do someone have access to the schematics ?

Thanks for your help!
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Old 30th October 2008, 06:31 PM   #3
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Default no one ?

Anyone could help me ?
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Old 3rd November 2008, 07:51 AM   #4
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Default Potential thermal fuse problem

Many power transformers have a internal thermal fuse that opens when the transformer temperature goes to high. Blowing of this fuse does not necessarily mean that the transformer itself is really bad.

If a blown thermal fuse is the problem then the only way to fix it is to dig out the fuse which could be just under the outer layer of insulation or the bottom of the windings and replace it. This is not always an easy job. The alternative is to replace the power transformer when the primary windings measure to be open.

Some transformers have a extra wire that connects to one side of the thermal fuse which makes it possible to bypass the thermal fuse if that is desirable by doing some external rewiring.

Safety is an issue so it is important to know what you are doing before making any circuit changes or by passing safety devices. Many good power transformers have gone to the dumpster because of a simple blown internal thermal fuse.
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Old 3rd November 2008, 07:57 AM   #5
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Default Added comment

After re-reading the posts this is likely not your problem but it is something to keep in mind since it is a fairly common problem.
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Old 3rd November 2008, 09:45 AM   #6
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Default After a little more thought

Since I know nothing about the A-471 my comments below are speculation but not out of the ordinary for audio equipment that may have some sort of microprocessor for control.

I assume that the A-471 was brought onto the market around 2000 and that it has a remote control. If it has then I would assume that this places a requirement to have some computer control over its functions which includes on and off and front panel display. During my years of repairing all sorts of audio equipment I have run into a number of circumstances when power was not being applied to the microprocessor or that the microprocessor was held in a continuous reset state.

The microprocessor, if present is typically built into front panel circuit board. The microprocessor has to have power and must be executing its internal firmware code to allow local or remote control. If there is a display then the display will typically show nothing if the microprocessor is not executing its internal software code. Power to the microprocessor would typically be provided by a very small 5 volt power supply which is always on when the power plug is plugged into a hot AC outlet. The microprocessor can be held in a reset condition due to a parts failure.

There have also been a number of occasions where I have seen microprocessors locking up and thus no longer being able to execute its code. Since it is not uncommon practice to have some kind of backup battery system built in to save the state of last use it will maintain the invalid condition until the microprocessor memory is cleared. Once this is done it can reboot from the start of its internal software code and may be able to function properly again. To clear this type of condition requires that the power to the chips memory be removed or a manual memory reset forced by whatever means are available. If there is a microprocessor failure then this wont help.

As I said I don’t know anything about the A-471 but perhaps the things I mentioned may be helpful in isolating your problem. Perhaps other persons can give additional hints.

Are you able to verify that there are at least some DC voltages present or not in the A-471?
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