Alpine MRV-1000 repair questions - diyAudio
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Old 6th February 2007, 11:05 PM   #1
spooney is offline spooney  United States
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Default Alpine MRV-1000 repair questions

I've got an alpine mrv1000 with no output.It powers up fine but just doesn't play.I have found two shorted transistors in one channel and the other channel looks fine.My question is that if the transistors are shorted how come the fuse didn't blow?And if the fuse didn't blow why doesn't the other channel work?Does this amp have a different protection circuit than normal?Also just wanted to check a couple part numbers real quick before I buy.Is an A1265N the same part as an 2SA1265N?And like wise with the C3182N.Would a 2SC3182N be the same part?
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Old 6th February 2007, 11:43 PM   #2
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2SA1265N is the correct part number.

The amp has independant power supplies. Are you sure the supply for the dead channel is operating (producing rail and regulated voltages)?

Each supply is independently fused.

If the amp has good protection circuits, the fuse won't blow because the supply will be shut down when a fault is detected.
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Old 7th February 2007, 12:11 AM   #3
spooney is offline spooney  United States
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I'm getting some real funny ohm readings off of the fets in the power supply of the channel with the shorted output transistors.I'm thinking they are dead or not far from it.The two diodes(rectifiers?they look like transistors) right next to them are reading differently than the ones in the other channel but i'm not sure if that is because of the fets or not.when the fets are removed from the board will they read like a transistor from leg to leg as far as resistance is concerned?
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Old 7th February 2007, 01:21 AM   #4
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With...
Meter set to DC volts
Power applied to the amp (including remote)
Black meter lead on the chassis ground terminal of the amp

What voltage do you read if you touch the red lead to the center leg of the FETs?

What voltage do you read if you do the same on the center leg of the rectifiers?
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Old 7th February 2007, 03:42 AM   #5
spooney is offline spooney  United States
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Heres what I found Perry.With the Black meter lead on chassis ground,meter set to dc volts, and red lead on the center leg of the fets I'm getting 12.7 volts on all fets.The rectifiers are a different story.In the channel without any shorted output transistors I'm getting -34 volts on the center leg of the first rectifier(F10P20FR) and on the second rectifier in that channel i'm getting nothing.That part is a F10P20F.Now onto the other channel with bad output transistors.I'm getting nothing out of the center leg of the F10P20FR.Same goes for the other part on that side(F10P20F).I also noticed a bulging cap on the side of the amp with good outputs right near the rectifiers.16 volt 220 microfarad
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Old 7th February 2007, 07:34 AM   #6
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On the side with -34v, I'd suspect a broken connection on the rectifier (either a broken leg or a bad solder connection).

Using the same setup as before, measure the voltage on the first and third legs of the FETs in the supply that has no output. If the voltage on the first legs are near B+ voltage, and the third leg is near ground (0 volts), the FETs have failed. If the voltage on the first leg is almost precisely 1/2 B+, switch your meter to AC volts and measure the voltage on the 4 outer legs of the rectifiers in that channel.
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Old 7th February 2007, 09:41 PM   #7
spooney is offline spooney  United States
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well the FETs in the channel with bad outputs are done.12 volts on the first leg and 0 on the third.The resistors feeding the fets all have funny readings.Is that because of the bad fets or should these resistors be replaced as well?The ones in the other channel all read right around 100 ohms and the ones in the bad channel are all over the place.Even though the fets didn't measure half battery voltage I checked the ac voltage anyways.It was approximately .280 volts. The rectifiers in the good channel all measured 46.5 ac volts on their outer legs.Is there a better component available to replace the irfz44n FETs?Originals are easy to find just wondering if there is any room for upgrade as long as I'm inside.Also I was wondering if that -34 volt reading could have anything to do with the shorted capacitor that is in close proximity to the rectifiers?
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Old 7th February 2007, 09:46 PM   #8
spooney is offline spooney  United States
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somethings else I just noticed that I'm not sure of is that the power on LED is dimly lit when power and ground are applied.When remote turn on power is applied it gets real bright as it should.Don't know if that helps or not
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Old 7th February 2007, 10:13 PM   #9
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Remove the defective FETs and measure the resistance of the 100 ohm gate resistors. If any are out of tolerance, replace all 4.

There are two 110 ohm resistors that pull the gate voltage down. One or both of them may be burned.

The drive circuit in this amp is weak. I wouldn't recommend using a substitute FET.

the -34v is the negative rail voltage. I'm not sure what it's supposed to be. I'd expect it to be a bit closer to 50v but 35 could be correct. Did you find the reason you didn't have the +35v on the other rectifier in that channel? You may have to remove it from the board to see if the leads are broken. Sometimes they break inside the plastic and don't look broken until you pull on them individually.

Caps often overheat when there is too much ripple current. If the rectifier is defective, that could cause high ripple current.

If one of the 494s is defective, that may be able to cause current to feed back to the LED. It may also be due to the FETs being shorted. Hopefully, after you pull them, the LED will only light up when remote is applied.
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Old 7th February 2007, 11:27 PM   #10
spooney is offline spooney  United States
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just got a look at the solder side of the circuit board and holy crap. Check This out.this ground trace is trashed.I'm surprised it even turns on.How do I go about fixing that?I removed the fets in the bad channel and the gate resistors are ok.I've yet to find any reason why I wasn't seeing 35 volts on that other rectifier.I'll probably take a closer look tomorrow.I'm getting kind of tired of staring at this thing for the day
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