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Old 5th February 2010, 12:21 AM   #31
spooney is offline spooney  United States
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Its a volt or two if I remember correctly. I will have to check it in a bit when I do some other testing and I will have the exact difference then. I have a feeling my test deck has different rca voltage from one channel to the other and this may be the reason for the difference in output.I really need to find a new test unit.
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Old 5th February 2010, 12:25 AM   #32
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Swap the RCAs or measure the voltage directly on the RCA cables to determine if it's the head unit.

If it's not the head unit's fault, disconnect the load, drive the amp to near clipping and measure the voltage there. Post the voltage you read on each channel. Measure directly across the speaker terminals for each channel.
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Old 5th February 2010, 04:49 AM   #33
spooney is offline spooney  United States
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Measured the rca output of my deck and they are pretty close. They are within millivolts of each other. The difference in output between the 2 channels on the amp is approximately 1.3 volts ac regardless of which rca is feeding the channel. I noticed the rail votage is slightly higher in the repaired channel. The original channel is +/- 45.3 volts and the repaired channel is +/- 45.8 volts. Is the difference is rail voltage significant at all? Also i should note the gain pot is damaged. It appears to work correctly but it spins all the way around. It does not stop in the max or minimum position
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Old 5th February 2010, 12:54 PM   #34
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VR801 and VR802 set the rail voltage but the rails in the amp are close enough.

If the voltage difference is 1.3v at ~30v AC, that's insignificant (less than 1/2 dB).

Did you try running it bridged to see if the same channel ran hotter?
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Old 5th February 2010, 03:51 PM   #35
spooney is offline spooney  United States
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yes the one channel does run hotter bridged. I think I know at least part of the reason why now. I disassembled the amp last night to clean up the heatsink and add some new compound and it appears that at least one of the outputs is not seated properly. Even with it screwed down I can push down on it and see the compound squeeze out from underneath it. I have to resolder the leads so that it will seat properly and/or come up with a better way to clamp it down.
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Old 5th February 2010, 04:02 PM   #36
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Desolder it completely and remove it to confirm that there is no foreign material between it and the sink or between the sink and the insulator. Reapply heatsink compound (not too much) and tighten the mounting screw. Apply pressure to the face of the transistor near the legs to displace as much compound as possible. When soldering the center leg, apply a bit of pressure to the leg and bend it over on the bottom of the board and solder the connection. This will ensure that there is a tiny bit of spring tension pulling the transistor to the sink. Only do this for the center leg. Solder the others with no tension.
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Old 6th February 2010, 06:16 PM   #37
spooney is offline spooney  United States
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I removed all the outputs in that channel and checked for debris. None to be found. I then reapplied heatsink compound and soldered them back in as you described. They still seemed kind of loose to me so I fashioned a sort of spring clip/clamp down to hold them in place. I had to use a larger screw for one of the outputs as the hole was stripped from trying to tighten it down too much. Turned out this and or my clamp down was a big mistake. I played the amp for a few minutes and then that output failed. When I removed it I could see that the new screw had pulled a nice size metal shaving out and left it under the transistor.

Seeing as all the holes for the output mounting screws were starting to strip I had to come up with a new way to hold them down. I drilled through the original hole with a slightly larger drill bit. Then I countersunk the bottom of the little heatsink plate just big enough to fit the head of a 4-40 flat head machine screw.On top I am using a nut,lockwasher,and flat washer to hold the transistor in place. Now I can clamp them down tighter than ever and not have to worry about them stripping again. Using this method in addition to soldering as you described earlier Perry I am happy to say that the outputs are now seated firmly.

Instead of the original 2sa1265 and 2sc3182 I am trying out fja4210 and fja4310 as outputs just because I happen to have a few on hand and fairchild list them as a direct replacement for the originals. I haven't been able to run it hard yet but at low power it seems to be working well.The output is clean and I am not seeing any of that oscillation that I had before. Also now the output is a lot more closely matched from channel to channel. At the most I am seeing .5 volts difference but over much of the range it is closer than that. In addition to replacing the outputs I also had to replace one of the small driver transistors mounted next to the outputs. The way things have been going with this amp I almost postive once I get this channel squared away the other one will fail shortly after. I refuse to let this thing defeat me though plus it gives me something to play with in my spare time.
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Old 6th February 2010, 06:36 PM   #38
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When doing this type of machining (which is often required), the drilling creates a small raised area around the perimeter of the hole. This needs to be knocked down so that the transistor can lay flat on the sink. Sometimes it's not obvious unless you sand the area lightly with fine sandpaper. Then it's obvious and you can see how much material needs to be removed.
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Old 6th February 2010, 06:41 PM   #39
spooney is offline spooney  United States
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There was a small ring of aluminum around the newly drilled holes that I sanded down. Forgot to mention that step.
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Old 18th May 2013, 11:07 PM   #40
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can someone please send me the documentation on alpine mrv 1000 ????

got my hands on this amplifier

I read on the net that it was testet and put out a 600 and some watts.

really?
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