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problem with amp....? Answered

there is power but no sound output,there are relays in side that click on iv have a prob and there is power to about half the board just not out put stage and i know that there is a speaker protection that is probable not letting power through for some unknown reason\r\nsansui au-x410r rated at 180 w   240v
does any1 have a surgestions on problem or how to get hold of a service manuel



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Best Answer 10 years ago

Most loudspeaker protectors also provide a 'de-thump' facility. When the amp is turned on, the speakers (or power to the main amp outputs) is not immediately connected. There is a time delay before the relay clicks in and the amp now does it's thing. Normally these types of circuits pick up power from the rectifier bridge (AC side), rectify it and put that power through a time delay circuit which then powers the relay. The circuit also disconnects the speakers the moment the main power is switched off. The idea is that the circuit detects when power is applied and when it's removed, stopping loud thumps being produced by the speakers (which can damage them). To make matters more interesting, the same circuit (with a few more bits added) can detect if the amplifier is faulty (applying DC to the speakers) or is clipping (over-driven - also applying DC to the speakers).

First things to check is the diodes in this circuit, then capacitors. If these test OK, move on to the transistors and the relay itself (coil may be open circuit).

If the relays click on the moment you apply power, the circuit may be behaving as if there is a fault in the main amplifier. If the circuit uses transistors for the main outputs, test to see if the are short-circuited. If the amp uses an STK???? hybrid chip, replace it as it is most likely toast. STK hybrids are dreadfully unreliable.

Good luck. I'll see if I've got any circuits that may suit this amp (or similar models) and let you know.


Answer 10 years ago

hi thanks for your reply has been very helpful. iv checked diodes there ok caps are ok to one of the smaller ones is running at alower rate to another of same value on same board not main cap there ok as are the transistors one again running  lower power then other of same value... may being down to the capacitor.... im not to sure how to test the relay iv not had to do that before....
i tested the transistors they work ok
i ran a signal through the amp to test ceramic resistor and slipped with prob made a nice crack and a bit of smoke i think its ok though re tested every thing  and no change to the components.. heatsink is getting very hot now with no signal passing through so must have do something