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Old 18th November 2007, 07:31 PM   #1
jol50 is offline jol50  United States
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Default working on a alpine mrv

It is a 1002 and looks like a wire might have shorted on the outside case at some point. So far I have found what must be a big inductor in the corner for the power on one side has blown the ground. The rest of that side seems ok, fets and gate resistors seem good. On the other side was some smoke...two fets blew hard and there are two gate resistors away from the fets that smoked. The 4 resistors near the fets have different values than good side (but could be due to the upstream ones being trashed with much lower ohms than other side) but they are not discolored.

Replacing the IRFZ44s is obvious, should I do the other side too? Can I get the color codes off the resistors on the other side or should I order a manual....any other likely issues I should check? I never tried to power it up, guy said it quit one day but light would come on.

As I recall the upstream resistors show about 110ohm and gate show 10.5 on good side, bad side show 10 upstream and 8.5 at fets. There are two running into 4 resistors at the fets, though I imagine this is a common amp to see for some of you.
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Old 20th November 2007, 07:39 PM   #2
jol50 is offline jol50  United States
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Got to work on this more, all 4 transistors on that side were shot. Now the gate resistors are showing near the same ohms as other side, even the two smoked ones. I don't think I have 4 IRFZ44, but can I put 2 good testing used ones in just to see if it fires up, one on each side until I get parts? Output resistors all show very high ohms.

Also see why that ground popped, the other one is grounded to the case and only this one grounds to negative also. Fixed that.

It seems like each channel is all separate, so I am assuming I don't have to mess with the other side unless I want to.
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Old 20th November 2007, 08:21 PM   #3
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You can install one FET per primary winding and, if there are no other problems, the supply will operate normally. Clamp the FETs in case there is another problem.
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Old 20th November 2007, 08:39 PM   #4
jol50 is offline jol50  United States
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Thanks again Perry, I was thinking I could if it was not asked to do much. Man, that is a lot of screws to put back in.... lol, this is getting to be habitual. However I'd be really happy if that is all that is wrong with it.
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Old 21st November 2007, 04:42 AM   #5
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If this amp is like the other Alpines I've worked on, the transistors are mounted to aluminum plates. The plates are held on by only a few screws. You remove the transistors with the plates. You don't have to remove the mounting screws for each transistor unless the transistor has failed.
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Old 21st November 2007, 06:53 AM   #6
jol50 is offline jol50  United States
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It is this one here: http://ampguts.realmofexcursion.com/Alpine_MRV-1002/
I didn't see any plates. Don't have any 44s, they were Sanken ones I replaced with 44s. I'd rather wait until I order the parts and not chance anything. Started on two other amps and fixed a problem in each, but both slapped me by not working and here I was doing so well. oh wait, here I am: lol!
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Old 21st November 2007, 07:20 AM   #7
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If the transistors were on 'risers', those are likely plates that come out of the sink. You may need to pry them gently (screwdriver between plate and sink). You should be able to see grease displaced from under the plate where the plate meets the sink.

There's a screw just above (to the side of) the driver transistors. It must be there to hold the plate down. They wouldn't have a screw there otherwise.

Look at the attached image. It's a different model but it uses plates similar to those in the older amps.
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File Type: jpg img_5260x.jpg (64.4 KB, 206 views)
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Old 21st November 2007, 07:21 AM   #8
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This is an exploded view of an amp similar to yours.
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File Type: gif clipboard01x.gif (14.2 KB, 189 views)
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Old 21st November 2007, 03:17 PM   #9
jol50 is offline jol50  United States
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I'll look at it, there was an extra screw so maybe it works that way....doh. I found a couple IRFZ44 in some junk China amps but not sure I want to use those just to test, want to make sure this amp is good/stays good. Or are they ok?
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Old 21st November 2007, 10:19 PM   #10
jol50 is offline jol50  United States
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Looking to order some and the ones they have in stock are IRFZ44NPBF (?) from IR at Mouser. Stupid question but even the data sheet says not a thing about the suffixes.
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