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Old 17th May 2011, 11:12 AM   #1
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Default Alpine MRD_M605

Wondering if anyone knows where the driver transistors for the power supply fets are located on this amp?? Like whats the board locations
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Old 17th May 2011, 12:06 PM   #2
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There are none. The 220 ohm resistors are used to pull the drive signal back to ground. Make sure that they're within tolerance.
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Old 17th May 2011, 12:19 PM   #3
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They all measure 218.5 ohms.

The problem im having is the fets are heating up within 10 secs to the point i cant touch them without burning my fingers
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Old 17th May 2011, 12:22 PM   #4
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Did you use exact replacements for the PS FETs?

What's the DC voltage on pin 4 of the 494?
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Old 17th May 2011, 12:30 PM   #5
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I dont know what the orginals were the amp was brought to me with the IRF3205's in it that werent orginal.

The voltage on pin 4 is : 3.67 volts
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Old 17th May 2011, 12:40 PM   #6
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If the DC voltage was 3+v on pin 4 and the FETs were getting hot and the gate resistors are within tolerance, there is definitely a problem.

The original FETs were 3205s according to the service manual.

Did you try pulling the rectifiers?

Does it have any shorted outputs?

Are you sure that the voltage on pin 4 was that high when the FETs were hot?

How much current is it drawing?
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Old 17th May 2011, 12:46 PM   #7
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I have to go do a few things ill get back to you on this later today
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Old 17th May 2011, 01:05 PM   #8
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Ok Guess my plans fell thru anyway.

All outputs are out of the amp.

When i power it up it idles around 2 amps of current.

The fets still get hot.

The voltage on pin 4 when the fets get hot is:0.46 volts

Rectifiers are still in the amp right now Want me to pull them?
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Old 17th May 2011, 06:41 PM   #9
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2A shouldn't make the FETs get hot that quickly if they're being driven properly (they probably are not). You can probably try pulling the rectifiers but it probably won't help if the outputs are out of the circuit. If it does not, install only Q906 and Q907. Do the FETs run cooler?

If not, pull all of the power supply FETs and check the gate drive signal to confirm that both are clean square waves that go to ground cleanly.
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