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Amplifier troubleshooting

Discussion in 'Troubleshooting and Repair' started by masterguns, Aug 20, 2010.

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  1. masterguns

    masterguns

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    Aug 18, 2010
    Another poster started off his thread by saying he was a computer geek and not an electronics one and asking the forum to please bear with him. In this being my first post, I'm here to ask the same as I try to resolve an issue with my car amplifier. I'll try to be as descriptive as possible and ask that anyone trying to help ask me any questions if you need clarification. Apologies in advance, the following reads more like a story than a technical description.

    To the issue at hand. My car amplifier (specs below) has an issue with the remote on/off feature. One day, per my mistake, the ground came loose and the protection light came on. I promptly reconnected the ground and everything was supposedly just fine. Ever since, however, the amp has the annoying habit on turning itself back on a few minutes after the head unit turns off. It will remain on, draining my car battery, until the power supply is pulled. After months of frustration, manually plugging and unplugging the power lead, I attempted to troubleshoot the problem myself. I opened the amp and did a visual inspection. I found a single rectifier with brown grime on it, but that's it. I know that's not much to go on and no guarantee that that's where my problem lie, nevertheless, I removed the rectifier. I then tried to find a replacement hoping that would cure the issue. The rectifier is labeled: "FMU22U 71 > 15". I assumed FMU22U is a model number and 71 > 15 refers to current. Doing the little bit of research I've done, and maybe someone can clarify this, a rectifier converts AC to DC current. I assume 71 > 15 is referring to amps or volts. I tired finding a replacement to no avail. Apparently FMU22U is a model # unique to a specific manufacturing company. I do believe it is a kin to a TO220. There's all different kinds, however, and I have no idea the difference between them. At this point, I'm in a little over my head. Like I said before, I am not an electronics geek so beyond doing a visual inspection, I'm not sure what step to take next. I'm not even sure I'm on the right track.

    I do believe, though, I can rule out a problem with the remote lead itself. I measured the voltage with the HU on and off and they appeared normal.

    I really just want to ask the help of those who are more adept at this subject than I. If you have any ideas or think you can help clarify some of my confusion, or if you want to try to help me figure this out, I ask that you please post your thoughts. I sure would appreciate it. I would love to be able to repair this amp myself rather than pay a shop or buy a new one. Thank you in advance and again, I apologize for being so green. :)
     
    Last edited by a moderator: Aug 20, 2010
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Is it still under warranty?

    Have you investigated repair options?
     
  3. masterguns

    masterguns

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    Aug 18, 2010
    I wish it was under warranty, would make things easier. No shops in town do this kind of repair and it would make more sense to buy new than to pay shipping and repair costs elsewhere.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    A quick search for FMU22U reveals nothing. Maybe someone else can help.

    TO220 is just the package it's in -- millions of components come in this package.

    Do you know it's a diode? How many legs does it have? How did you remove it?

    Can you provide us with a photograph of it?
     
  5. masterguns

    masterguns

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    Aug 18, 2010
    Here's the best pic I could take. I carefully removed it using a soldering tool. You can make out the markings. The other leg broke off later after removal. There's also a pic of the board. You can see where it was removed from.
     

    Attached Files:

  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You need to hold the camera still :)

    But at least we can see what it is. Clearly a double diode, and presuming you weren't tremendously rough removing it, a leg falling off is generally considered to be a sign of failure :D

    I can't find a reference to the device, bit I'd take a stab at it being a dual diode 75V 15A.

    This is the closest I can find, unfortunately it's exactly the wrong way around, and only rated for 8A.

    I presume there's something holding it to the heatsink?
     
  7. masterguns

    masterguns

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    Aug 18, 2010
    Yes, I don't know what you would call them, but there were small metal plates with a single screw that sandwiched each to the heatsink.

    (Sorry bout the pics, older camera, no EIS. :p)
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    As long as they were individually screwed to the heatsink,and not sandwiched by a single piece of metal, you won't have issues with a slightly different package having a slightly different height.

    The original device seems to have a full plastic case, and it is important that you replace it with one in a similar package (or at least one with an isolated tab) or you'll short things out.

    regards the camera, use a tripod, or rest it on something when you take the shot, or have LOTS more light.
     
  9. masterguns

    masterguns

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    Aug 18, 2010
    Thanks for the advice on picture taking. Here are a few somewhat better pics, they won't win any awards, but at least you can make out the markings. :p You can see they were not individually screwed in. They each were thermal bonded with an anchor plate (pictured not screwed in where the diode was removed). Each plate held down two diodes each.

    When you say isolated tab, do you mean plastic casing?

    The specs for diodes can be a little confusing to me. When I'm searching for a replacement, what specs should I be looking for exactly? A dual diode 75V 15A?

    And let me also take a moment to thank you, I really do appreciate you helping with all of this. :D
     

    Attached Files:

  10. Resqueline

    Resqueline

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    Jul 31, 2009
    One thing with that diode is the way its diodes are pointing. Most dual diodes have'em pointing to the center pin, so the selection will narrow itself pretty much right there.
    I'm sorry but I don't have any suggestions off the top of my head. What's the voltage rating of the two big capacitors, and what's the wattage (& fuse) rating of the amp btw.?
     
  11. masterguns

    masterguns

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    Aug 18, 2010
  12. Militoy

    Militoy

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    Aug 24, 2010
    FMU-22U appears to be a Sanken fast-recovery diode in a TO-220F package. Looks like 200V 10A. Trr is 0.4/0.18 uS. I didn't spot the polarity of the U suffix on their website, during a quick scan - but the S suffix has cathodes connected to the center pin; the R has the anodes to the center. I'll bet a quick look at some other Sanken parts would give you a clue as to polarity of the U part - or, you could look over the circuit where it's connected, and apply a little logic. Good luck!

    EDIT - I had a chance to look again at Sanken's website over lunch - and spotted a clue on the U suffix part. It looks to be a series diode array - with anodes pointed to left. Fairchild makes a similar part that might cross close enough - FEP16DTD. In stock at Newark for $1.09.
     
    Last edited: Sep 1, 2010
  13. shrtrnd

    shrtrnd

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    Jan 15, 2010
    Hopefully *steve* will get back to you on your query to him.
    He's right, make SURE you've got the TO-220 case isolated from the heat sink, so you don't short it out. Mica isolator, or something similar, ....if you saved whatever you took from the assy when you removed the TO-220, you may be able to reuse it.
    Just wanted to get my 2 cents in, in case you replace the part, before *steve* gets back to you. You don't want to fry the new part.
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The major issue is that the original has no electrical connection to the tab (it's not metal).

    If you get one with a metal tab, ensure it's not connected to any of the leads, and if it is, get the correct insulating material(s).

    Also double check that the diodes are pointing the correct way.
     
  15. Militoy

    Militoy

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    Aug 24, 2010
    I hadn't zoomed in on the second photo before - so I missed the schematic screened on the part. I guess at least Sanken's catalog is accurate. I suppose it would be much simpler to find a sub in a TO-220F package, than using a sil-pad under it - but I notice that most fast recovery series diode arrays seem to be arranged in the opposite way - with cathodes pointing left.
     
  16. masterguns

    masterguns

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    Aug 18, 2010
    Wow, lots of good info, thanks everybody. I've been trying to educate myself enough to figure some of this out. A lot of the specs still don't make sense to me, so I'll just ask, Do you still think the FEP16DTD part might work as a replacement? Why, why not?
     
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