Working on a G-7000. The service manual I have generally agrees with the driver and power supply boards, and I can adjust the driver board no problem, put in new trannies and it works great. Until you turn it up too far and the protection kicks in. The right channel still works, but the left always blows the NPN device. I have checked all the components and did find a blown 220 ohm resistor and 220 ohm trimmer on the driver board but it still has this problem. HELP !
G-7000 protection circuit
- Thread starter OSPREY
- Start date
Define 'too far'...
What are you setting the bias current at? Forget the Sansui procedure of using an ammeter in place of the fuse...take a reading directly off of the output emitters and set the bias current at 30mA.
Are you setting DC offset properly? What are you using for a load??
...and I'm also wondering what you're getting for replacement transistors. Lotsa fake devices around.
The manual I have says to measure the voltage drop across the emitter resistors to set the bias current to roughlt 15 ma.
Yes the output offset was nulled.
Using a 10 ohm power resistor for load.
What I found out is that the replacement transistors I was using had a much higher hfe than the originals. By increasing the value of the base drive resistors I was able to make this work very well but will be looking into putting it back into original condition.
Thanx for the help.
Dave.
Yes the output offset was nulled.
Using a 10 ohm power resistor for load.
What I found out is that the replacement transistors I was using had a much higher hfe than the originals. By increasing the value of the base drive resistors I was able to make this work very well but will be looking into putting it back into original condition.
Thanx for the help.
Dave.
