Alpine MRD_M605

mike49504 · 17th May 2011, 11:12 AM

Wondering if anyone knows where the driver transistors for the power supply fets are located on this amp?? Like whats the board locations

Perry Babin · 17th May 2011, 12:06 PM

There are none. The 220 ohm resistors are used to pull the drive signal back to ground. Make sure that they're within tolerance.

mike49504 · 17th May 2011, 12:19 PM

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

Perry Babin · 17th May 2011, 12:22 PM

Did you use exact replacements for the PS FETs?

What's the DC voltage on pin 4 of the 494?

mike49504 · 17th May 2011, 12:30 PM

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

Perry Babin · 17th May 2011, 12:40 PM

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?

mike49504 · 17th May 2011, 12:46 PM

I have to go do a few things ill get back to you on this later today

mike49504 · 17th May 2011, 01:05 PM

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?

Perry Babin · 17th May 2011, 06:41 PM

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.

17th May 2011, 11:12 AM	#1
mike49504 diyAudio Member Join Date: Sep 2006	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

17th May 2011, 12:06 PM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	There are none. The 220 ohm resistors are used to pull the drive signal back to ground. Make sure that they're within tolerance. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

17th May 2011, 12:22 PM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Did you use exact replacements for the PS FETs? What's the DC voltage on pin 4 of the 494? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

17th May 2011, 12:40 PM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	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? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

17th May 2011, 06:41 PM	#9
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	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. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links


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17th May 2011, 12:19 PM	#3
mike49504 diyAudio Member Join Date: Sep 2006	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

17th May 2011, 12:30 PM	#5
mike49504 diyAudio Member Join Date: Sep 2006	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

17th May 2011, 12:46 PM	#7
mike49504 diyAudio Member Join Date: Sep 2006	I have to go do a few things ill get back to you on this later today

17th May 2011, 01:05 PM	#8
mike49504 diyAudio Member Join Date: Sep 2006	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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