Sony XM-GS400

[Perry Babin]

2SD1898 if you have it. If not, an MMBTA06 will allow testing if you can make the connection to the pads.

 

[S Merlington]

Ok I replaced it with a 2SD1898..

Now I have 4.98 volts on all of the gate pads..

I get 5.46 volts on pins 9 and 10 of the 494

Now to put the fets back in and disable the protection circuit..

 

[S Merlington]

After removing q913 and jumping pin 16 to pin 7..

The amp Powers up and burnt q911 .. I still have full rail voltage on all 4 channels measured directly across the speaker terminals ..

 

[S Merlington]

Ok more checking into this amp..

I'm Getting 30 volts on all 3 legs of every output in this amp..

Do you happen to know what causes this ?

 

[Perry Babin]

If there is a negative rectifier, it's connection to the outputs has to be broken.

Do you have a 0-24v waveform on the center legs of all power supply FETs?

 

[S Merlington]

Yes I have 0 to 24 volts waveform
On all power supply fets ..

The negative rectifier on this amp I'm assuming is the FRH10A15 and the positive rectifier is the FCH10A15?

 

[Perry Babin]

FRH is the negative.

 

[S Merlington]

Ok removed them from the board and cleaned the board and put them back in .. Amp powers up and plays clean audio on 3 of the 4 channels ..

The right rear channel still has issues I get -7.49 volts measured directly across the speaker terminal..

I also get 7 volts on base and the emitter for both outputs in that channel ..

Possibly a leaky driver or output?

 

[Perry Babin]

Is that the 400 series channel?

 

[S Merlington]

Yes

 

[Perry Babin]

I don't know what was done to that channel but it has been repaired. Go back over the work, clean it up, check all connections. You may be able to compare readings from one of the other channels to see of there appears to be any leakage. If not, you'll have to pull the drivers and other components to check them.