Remove the suspect FET and check it. You can operate the amp with it out of the circuit.
Also, check the 10 ohm resistor connected between the collector of the MPSA56 driver and ground. They sometimes open or go out of tolerance.
Also, check the 10 ohm resistor connected between the collector of the MPSA56 driver and ground. They sometimes open or go out of tolerance.
Will you show me the resistor you mentioned? Are they the ones I have circled in yellow in the attached photo?
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Resistors check good.
Pulled PS FET is shorted.
Amp powers up but the PS FET's on the left side of the board are still immediately getting hot.
Pulled PS FET is shorted.
Amp powers up but the PS FET's on the left side of the board are still immediately getting hot.
Clamp the FETs if you need to protect them from overheating.
How much current is it drawing?
Compare the drive for the left side to the right side. Do this on the emitter legs of the drivers for each side.
How much current is it drawing?
Compare the drive for the left side to the right side. Do this on the emitter legs of the drivers for each side.
As to the current draw...it is blowing the fuse on my multimeter but it showed 15 amps briefly before it popped the fuse.
The right driver emitter leg is reading +0.3 volts the left is reading +2.45 volts.
The right driver emitter leg is reading +0.3 volts the left is reading +2.45 volts.
MPSA06 voltage:
Right:
Leg 1: +.30
Leg 2: +.71
Leg 3: +.20
Left:
Leg 1: +2.49
Leg 2: +2.74
Leg 3: +6.20
Right:
Leg 1: +.30
Leg 2: +.71
Leg 3: +.20
Left:
Leg 1: +2.49
Leg 2: +2.74
Leg 3: +6.20
Find the reason for no voltage on the collector of the right A06. It should be the same as the other side.
The resistor that is connected to it was bad. I also found the diode in the corner of the right side of the board was bad. I replaced both. Voltage readings are now the same. Amp now powers up without the PS Fet's getting hot.
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Is pin 1 still pulsing?
Is pin 3 of either of the protection transistors pulsing?
Is pin 1 of the 6488 pulsing?
Is pin 3 of either of the protection transistors pulsing?
Is pin 1 of the 6488 pulsing?
MSPA06 pin1: +3.47 volts
Protection transistors pin 3: +21.52 volts
Pin 1 of 6488: +4.5 volts
Protection transistors pin 3: +21.52 volts
Pin 1 of 6488: +4.5 volts
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6488 as well as the protection transistors are still out of the board. Jumper wire on pin 4 and 7 on 494 still connected.
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For the protection circuit transistors, the collector (pin 3) is at negative 7v. You need to see if you can find what's causing the collector of that transistor to be at rail voltage.
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