Sansui AU-7900 Problem

[Nagal]

Hi....

i have the sansui au-7900, the sound is normal but, but when I turn off the amplifier. there is sound Bukk in the speaker, there is a solution to this problem, I am afraid it will damage the speaker.

Thanks in advance

 

[donpetru]

In the first phase, you should check the relay that switches on loudspeakers. It is possible that the contacts of this relay have remained welded. So, check the relay RL601.
If the relay is OK, the DC Offset level should be checked on the output of each channel with volume potentiometer: minimum and maximum. And of course, will have to be checked, all capacitors on the audio signal path of the amplifier.

 

[Nagal]

Hi donpetru
How to cek dc offset level.

 

[huggygood]

sansui au-7900 service manual - Google Search

 

[donpetru]

Hi donpetru
How to cek dc offset level.

How to Measure DC Offset: 5 Steps (with Pictures) - wikiHow

 

[BobtheBuilderMLG]

Also, Nagal has the amp ever been restored? I just got done repairing the 7700 which is a similar amp that had a similar problem and then it blew the relay coil.

 

[Ian Finch]

Relays do fail with bad contacts but it may not be the case here, since you have sound but only have the dying amp. noise problem when you switch off. The noise is likely normal but the speaker relay should block it by opening as soon as power is cut. Probably, the protection relay is not being switched properly and many old amps show capacitor failures in the protection circuit that powers it. You can easily measure with a multimeter, when the relay coil is powered with 24 volts or not, when you turn on/off and deduce whether the contacts are opening. The manual describes and shows the details of the circuit it but be warned that this is an old design and some components will now be unobtanium. If you can't test this function or measure caps and semis properly, you will need practical help.
Sansui AU-7900 - Manual - Integrated Stereo Amplifier - HiFi Engine (register to receive free downloads)

 

[Nagal]

thanks to all, this Saturday I will check the sansui amplifier, because I have time on Saturday only.

 

[Nagal]

Hi all.
I tried to move the switch to connect (see picture) I only played the Sansui power with the Bluetooth pre-amp, the sound was normal and when the amplifier was turned off, the speaker had no sound Bukk.
according to the master, the damage is at the pre amp or power amplifier.

Thanks in Advance

 

[Mark Tillotson]

There's a worrying amount of corrosion on the outside - I hope its less affected internally.