HI all, able to shed some tips/advices for the above amp of mine tat has been wif me for quite a while?
I do understand tat the AU-717 was from the Sansui 07 series of amps, it was classified as the smaller bro to it counterpart AU-919.
All the while it has been working fine wif minor issue, the problem was from cold start to power on n i always had the habit of switching the speaker knob from selection speaker A to off wenever i tend to off the amp after some leisure listening n vice versa. Volume,Loudness,Subsonic n Tone will also be in off position if i happen to fiddle wif it but usually i hardly touch it. It is consider as a correct/proper procedure to switch off the amp or is there any other better alternative than this?
It won't do any harm to switch out the loudspeakers that way. Most people don't do it, and it should not be necessary.
So my issue lies in wenever i on the amp, turn on to speaker A from off position, i always experience some hiss/shassy soft sound from my L/R ch speakers. So in order to eliminate this disturbance, i switch back to off position on the speaker selection. Aft a preheat/warming of 10/15min or so, i switch back to speaker A n gosh the hiss/shassy sound is gone.
From a distance, without actually hearing the amplifier, it sounds like there is a part which is noisy until warmed up. This usually is an active device such as a transistor or integrated circuit but can also be a poor connection, or a passive part such as a resistor that has become noisy, or a capacitor that is leaky.
Is this noise in both channels, or in just one? If a power supply fault were the cause, you would probably hear the noise in both channels. If an amplifier fault, usually in only one.
Recently i pick up the courage to replace the E caps thoughout the output drive n power section. Of cos i did a lot of reading from various site etc... AK, Cdkands or audio review b4 i attempt the task. Those nasty glue on the pcb tat causes corrosion to various parts has now been cleaned n remove by solvent thinner. All caps has been replaced wif Nichicon/Elna caps of same value/voltage(105 degree celcius) not consider audio grade type cos i was on a budget roll. I did best of wat i could n i do admit its power section is one of the hardest part to rectify. Aft the cap change, the hiss sound still persist duing the initial switching on of amp.
My personal background is basically i know nothing bout electronics, but i do know desoldering/soldering skills of parts n simple measurement of caps n voltage.
Any generous feedback wld be greatly welcome, lastly tks
The yellow glue used by the Japanese to adhere parts to the circuit boards prior to wave soldering has turned out to be a real headache. As you note, it
can corrode the copper traces on the boards. It can also cause leakage between traces. In some cases (the Hi-Fi audio board in a line of expensive Mitsubishi Hi-Fi Stereo VHS decks was one that was legendary), the problem got so bad, involving such sensitive circuitry, that the only cure was to purchase a new board. Yes, it could cause the behavior you describe but other causes are more likely.
I'm thinking that some careful signal tracing and voltage measurements should be the next stage in troubleshooting your amplifier. That would be getting beyond the basic skills you have learned thus far. My instinct tells me that the first place I would be looking would be the differential input stage of the power amplifier, which in the AU-717 is a dual JFET. It is followed by another differential amplifier, this one comprised of two bipolar transistors. But that kind of noise could actually originate just about anywhere. WARNING: poking around in this circuitry is not for the unskilled; one slip of a voltmeter, oscilloscope or signal tracer probe could blow up a channel.
The service manual for the Sansui AU-517/AU-717 is available as a free download at Hi-Fi Engine. Registration is required, and it's free.
http://www.hifiengine.com/library/sansui/au-717.shtml
