Alpine MRV-100M Z48 substitute - diyAudio
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Old 27th December 2010, 09:28 PM   #1
Dr Zeus is offline Dr Zeus  United States
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Default Alpine MRV-100M Z48 substitute

Got this amp in needing all (2) new power supply fets. This amp uses two IRFZ48s.

I think I can use IRFZ44 for testing as I have some of those, but I also have a bunch of matching IRF3205 fets. I know the Z44s are ~15A less powerfull than the Z48s, but the IRF3205s are ~15A MORE than the Z48s, which tells me that IRF3205s might be the better choice. This amp has 4 larger output transistors and might benefit from the added power if it will work.

Would IRF3205s work with or without modification?

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Old 27th December 2010, 09:35 PM   #2
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As always, I'd suggest that you use the original replacement part. The Z44s will be fine for testing.

The drive circuit will determine what will work. What are they using for the drive circuit?
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Old 27th December 2010, 09:42 PM   #3
Dr Zeus is offline Dr Zeus  United States
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Theres an surface mount NEC brand C494GS under the PCB. The amp is using 10ohm gate resistors on the power fets. This is a small Alpine V12 amp.
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Old 27th December 2010, 09:47 PM   #4
Dr Zeus is offline Dr Zeus  United States
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This amp is strikingly similar to an Alpine MRVT303 like whats on the dvd. I can tell one or two things are different, but its generally the same layout. Biggest thing is my 494 is surface mounted on the BACK of the board where the T303 is on the front and through-hole.

C:\repair_tutorial\miscellaneousstuff\alpine\alpin emrvt303\repairnotesmrvt303.htm
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Old 27th December 2010, 09:48 PM   #5
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Does it use driver transistors?
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Old 27th December 2010, 09:53 PM   #6
Dr Zeus is offline Dr Zeus  United States
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There are no transsitors between the 494 and the fets. Its a straight shot between the 494 pins 9 and 10 and the fets (w/ an inline 10 Ohm gate resistor). One fet is going to pin 9, the next to pin 10 of the 494.
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Old 27th December 2010, 09:58 PM   #7
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I don't think the 3205s will be a good sub here. You can try them but you need to make sure that the 3205s run cool at idle when the power supply is at full (50%) pulse width.
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Old 27th December 2010, 11:30 PM   #8
Dr Zeus is offline Dr Zeus  United States
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Since I had quite a few 3205s I went ahead and put a pair in. The amp now powers up but still has issues.

The amp will play a clean sin wave... Unfortunately after about 4 seconds the rail voltage drops from 30v down to ~10 and the sound then stops. Its almost like the amp is going into protection or the 494 is being told to power the amp off. Im thinking the 3205s are not going to make the cut here.

Last edited by Dr Zeus; 27th December 2010 at 11:32 PM.
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Old 27th December 2010, 11:50 PM   #9
Dr Zeus is offline Dr Zeus  United States
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To be honest, Im not even sure how this amp is working for even 4 seconds. I measured the 494's irregular activities

C494GS

Pin 1: 0.001 (Blips to 0.250 for ~1 second then back to 0.001)
Pin 2: 0.88 & drops to 0.734 (after 4 seconds)
Pin 3: 0.085
Pin 4: 4v & Drops to .2v
Pin 5: 1.66 & Drops to 1.275
Pin 6: 3.7 & Drops to 2.8
Pin 7: 0.002 & Drops to 0.000
Pin 8: 8.89 & Drops to 5.10
Pin 9: Rises up to 1.335 after ~4 seconds
Pin 10: Rises up to 1.335 after ~4 seconds
Pin 11: 8.89 & Drops to 5.10
Pin 12: 8.89 & Drops to 5.10
Pin 13: 5 & drops to 4.10
Pin 14: 5 & drops to 4.10
Pin 15: 5 & drops to 4.10
Pin 16: 0.002 & Drops to 0.000
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Old 28th December 2010, 12:43 AM   #10
Dr Zeus is offline Dr Zeus  United States
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I think I figured this amp out. Its not the 3205s. I think someone tried to raise the rail voltage via the VR601 screw. Thats probably what burned out the power supply fets in the first place, and also what was shutting the amp off after 4 seconds.

The screw was all the way clockwise, so I turned the screw all the way counter clockwise. The amp stayed on, powered up with stable audio output. I'm presuming this MRV-100M is pretty close to an MRV-T303. The service manual of the 303 says to set the voltage to 53v +-1v so i did; the VR601 pot is turned only about 20% where as before it was all the way. This amp seems stable and hopfully fixed now.

Last edited by Dr Zeus; 28th December 2010 at 12:47 AM.
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