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Old 10th April 2012, 07:59 PM   #1
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Unhappy Need some help with alpine mrv-1002 PLZ

im having some trouble with my amp, i blew it up the other day because i was dumb and ran it on a low impedance lol ( knowing it was most likely gonna blow up, but i wanted to see what this amp could do). one channel in the and was messed the other was fine. the transistors in the power supply were all blown, one output transistor was blown and one other little one was blown not too sure what it was for, ( im not pro),

anyways i put all new parts in, and its working again, BUT, i cannot find a repair manual, ive changed output transistor b4 and i remember having to set the idle current, and i have no clue how to do it on this amp, there is a orange pot beside the transformer on each side, but i wasn't a 100 % on what it was for. and every once and a while, the one side will get all scratchy, then it will go away. if i turn it up it does it for a few seconds then goes away, ( like i said b4 im not a pro but i do like the challenge and the hands on learning)

so if anyone could help me out with any of my probs that would be Awesome,
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Old 11th April 2012, 12:23 AM   #2
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I don't have the service manual but it's available from pacparts.

The pots in the power supply are used to set the rail voltage. What output transistors are they using in this amp?
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Old 11th April 2012, 12:25 AM   #3
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they are using irfz44 transistors
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Old 11th April 2012, 12:27 AM   #4
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Those are commonly used in the power supply but not as output transistors. Are you sure that they're using IRFZ44s as output transistors?
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Old 11th April 2012, 12:44 AM   #5
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OH sorry, i didnt read the post properly , lol they are using b688, and d718, for the output, ive been using the amp all day, and the random crackling/ static noise disappeared, but i think that because the all the components have warmed up, i think im gonna turn it off put a fan on it, let it cool, then try it again to see if the noise comes back, since i changed the power supply transistors i should be making sure the all the rails are equal LOL, ,

there is two pots would one be for + rail and the other for -rail on each transformer, or is one pot for each transformer + and -?, sorry about all the questions, this is my first car amp repair, ive always did home audio,
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Old 11th April 2012, 01:16 AM   #6
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The pots on a similar amp are for each individual rail. I assume that they're the same on this amp.

The rail voltage probably isn't real critical on this amp but it definitely needs to be set to less than the working voltage rating of the rail caps. If you set it too high, the amp may run too hot, even if it's set below the WV of the rail caps.

The only way to know what the correct setting is is to get the information from the service manual (available from pacparts for $10+ shipping).

For the bias, I'd suggest setting it so that you have approximately 1mv (0.001v) across each of the emitter resistors. This should be done with no audio input and no speakers connected.
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Old 11th April 2012, 01:27 AM   #7
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ok thank you, awesome, i i checked the + and - rail voltages on both channels of the amp and they are all reading 43.8 so im guessing its good, because i didn't touch the other side, as for the idel current i dont see anything for adjusting it, im not really into buy the manual, because i probably wont have this amp for long and i will probably never see another one again, and im in the process of moving and such, so i dont even have the little $$ to get the manual, it was a stretch for me to get the replacement parts, LOL
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Old 11th April 2012, 01:28 AM   #8
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If the amp doesn't get hot at idle, the bias is likely OK.
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Old 11th April 2012, 01:43 AM   #9
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ok awesome, its been cool all day untill i was pushing it, thank you very much for your help it is very appreciated
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