I have a MS-275 that came in for repair due to leaky caps. I have replaced pws caps and rail caps. I also had to replace U8 (BA4560). I went ahead and replaced U6 as well.
Currently the amp powers up the driver circuit leds light up for a second and cut off. The audio outputs have shared rail voltage. I read no voltage across the bias control pot.
Currently the amp powers up the driver circuit leds light up for a second and cut off. The audio outputs have shared rail voltage. I read no voltage across the bias control pot.
Attachments
Was it working originally, with the leaking caps?
Does the entire supply shut down when the LEDs go out?
Does the entire supply shut down when the LEDs go out?
I did not power it after I saw the burn marks around the caps and fero fluid. The powersupply is stable. I did notice that there is 17v on vcc and 30v on bee of the op amps. I will have to pull out a personal one to verify this voltages.
Have you confirmed all of the flameproof resistors are within tolerance? (longshot but need to be checked).
DCV across R218 and R217?
DCV across R218 and R217?
Maybe I’m confused but i am not measuring any positive voltage.
-31 volts with black lead on ground red on amp heat sink.
Positive rectifier has 1v on center leg
Negative rectifier has -66v on center leg
-31 volts with black lead on ground red on amp heat sink.
Positive rectifier has 1v on center leg
Negative rectifier has -66v on center leg
U2 and U3, TO-92 case, near the black wires?
What if you place the black probe on the non-bridging speaker terminals?
What if you place the black probe on the non-bridging speaker terminals?
With the black probe on one of the non-bridging speaker terminals, do you have ±rail and ±regulated voltages?
You can't rely on the primary ground. That's why I suggested one of the non-bridging speaker terminals. The secondary center-tap of the transformer would be the same.
Black probe on ground (neg) spk terminal
7915
1= 0
2= -32
3= -30
7815
1= 15.34
2= 0
3= 32
These are voltages after replacing the negative voltage regulator. Now one channel is powering and one channel is not.
7915
1= 0
2= -32
3= -30
7815
1= 15.34
2= 0
3= 32
These are voltages after replacing the negative voltage regulator. Now one channel is powering and one channel is not.
I installed a used 7915 so it’s possible it could have been bad too. I was expecting -14.5 to -15.6