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sansui au-x701 trouble


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hello I'm new to this forum

I have a sansui au-x701 amplifier. A few weeks ago it made a nasty sound trough the speakers when turning on.  Now it sound like the speakers are blown, but they are not. (i have also tried other speakers) I have checked the output power transistors and they are good. I have donwloaded a schematic from this site. My next step will be to try and check some voltages on the power supply.

Anyone who has an idea what it could be?
The amplifier has performed flawlessly to this point.

A service manual would be wonderful

Thanks in advance.

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  • 2 weeks later...

I found the resistor mr17 and diodes mo4 and mo6 burned of. The problem is on the schematic i downloaded from this forum, i can't read the value of the resistor. It looks like 10 ohms, but i'm not sure.


it is on the power supply on page 15. Anyone who knows the value of this resistor?

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Yes it looks like 10 ohms to me also.
I've seen many different power supplies but never (I think) anything like MR8 and MR9 creating some kind of virtual ground.
Have you measured for low resistance right after mD4 and mD6?
I would measure both +32 and -32 to see if there is any difference in resistance.
Check also +31 and -31 series regulator transistors mQ3 through mQ6, zener, caps and fets. measure resistance right after these series regulators as well.

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I replaced the resistor with a 10 ohm, and also the two fmu-22s (m04 and m06) that had be "blown to peaces" Amp now plays like it did before, but i don't know what caused the problem.

I'm almost a bit sorry i fixed it because i really wanted to build a 2 x ucd180 amp :)

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