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Thread: Rotel RB-970bx

  1. #1

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    Default Rotel RB-970bx

    I have three rotel amps I recently moved to a new place. I wrapped all three of my amps in a seperate blanket and put them in the back seat. Drove about 30 miles no bumpy roads I unloaded them and hooked everything up and well the RB-970bx would not turn on. I use this amp for my surrounds using a denon avr 3801 as my pre. So I just hooked up the surrounds to the denon. I took the cover off the rotel and noticed 4 fuses 2 in the back 2 in the front. The 2 in the front were blown. What is strange is the RB-970bx was working fine when I unhooked it and have had it for 2 years with pretty much daily use with no problems. I replaced the fuses with the the same value and turned the amp on it came on for a second then the same 2 fuses blew. I looked everything over and dont see anything burnt or dont smell anything. My question is for you electronic gurus what do you think could be causing this and do you think a local shop could repair it. I dont want to spend to much on repairing it as I only paid $250 for it. I dont notice a difference in the sound over the denon. I did notice a difference going from the denon to the rotel on my mains but for the surrounds I cant hear a difference. My plan was to use this amp for a 2 channel sytem I would hate to throw it away. Thanks in advance for any advice.:)

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    Any advice on my problem? I posted this yesterday with no reponses yet:(

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    Most likely the move caused a marginal component to fail... perhaps some dust moved, perhaps something shorted... its immaterial at this point. The fact that fresh fuses are blowing indicates the amp has a problem. Taking it to a shop will cost bucks unless you know the shop well. Perhaps Ben will fix it or buy it from you.

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    I would take it to a local shop, and have them look at it. I would look at it for you no problem, but the shipping both ways would be pretty high. A local shop should be able to find a short pretty easy. Also you can replace the fuses with lower amp ones, and turn it on in the dark(cover off), and see if you see the spark. Don't try the fuse trick more than 2 times. You don't want to make a small problem a big problem.
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben

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    My advice is to get a can of compressed air and blow out the inside of the amp really well. Also, loosen the speaker terminals on the back of the amp and blow those off really well, and make sure that there are no teenie tiny frayed speaker wires touching anything, either inside the amp or on the back.

    It's just a guess and kinda a long shot, but if there's a thread of speaker wire inside the amp, that could cause it. If there's contact being made on the back of the amp, it would most likely cause only one side to stop working, but it's definitely worth a try.

    I hope this $5 idea can help you. Please keep us posted.

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    Thanks guys for the responses I have an air compressor I will try that first the insides look real clean brand new looking. If that doesnt work I will take it to a local shop. A suggestion from another forum was to get a meter and check the rectifiers for a short. Ben If I post a pic could you tell me where the rectifier is? I hope I spelled that right.
    Last edited by greg2350; 04-10-2009 at 02:28 AM.

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    Component failure is possible. Check between boards and the chassis for burn marks.
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    Quote Originally Posted by greg2350 View Post
    Thanks guys for the responses I have an air compressor I will try that first the insides look real clean brand new looking. If that doesnt work I will take it to a local shop. A suggestion from another forum was to get a meter and check the rectifiers for a short. Ben If I post a pic could you tell me where the rectifier is? I hope I spelled that right.
    I did have a Rotel with a blown rectifier once and it exhibited the same problem. A rectifier looks like this: http://www.germes-online.com/catalog...ectifiers.html

    Read this http://answers.yahoo.com/question/in...3053442AAlNNB2 on how to test them (the last answer).

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    Quote Originally Posted by anonymouse View Post
    I did have a Rotel with a blown rectifier once and it exhibited the same problem. A rectifier looks like this: http://www.germes-online.com/catalog...ectifiers.html

    Read this http://answers.yahoo.com/question/in...3053442AAlNNB2 on how to test them (the last answer).
    Thanks for the info I checked the rectifier with a meter and its gone dead hopefully I can get another one. Looks easy to replace im pretty good at soldering.

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    Quote Originally Posted by greg2350 View Post
    Thanks for the info I checked the rectifier with a meter and its gone dead hopefully I can get another one. Looks easy to replace im pretty good at soldering.
    You do not need to find the exact model number. This should do the job: http://www.radioshack.com/product/in...ductId=2062583

    Just make sure you orient it the exact way the existing one is oriented. (With the cutout facing the same direction)

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    Some pics of the broken rotel




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    The one on the left is the bad one isn't it? You can see a melted & arced area in the center.

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    Yes its the 1 on the left I just replaced it with 1 of the same value and when I turned it on the front 2 fuses blew. I will call rotel monday, again thanks for all you guys help.

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    Mann this sucks I really liked this amp had it for 2 years never pushed it hard sounded great. Hopefully it can be fixed. :(

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    Hey Greg, did you get the amp fixed?

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    Not yet I have been to busy to mess with it. I have some down time next week I will be looking into getting it fixed.

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    My Dad fixed and upgraded this amp. The original overload problem might have come from different things.. The variable resistor in one channel was shot (fell apart in shipping), so that channel was most likely overloading the supply. One of the transistors in the power supply was not properly attached to the heatsink and its case even changed colour...

    What caused dead bridge and the short? That's what I couldn't figure out, so I gave it to my father. One of the caps underneath the "dead" bridge was physically broken and shorted out. So the whole power supply was shorted and blowing the fuses.

    I replaced all bad components. The power supply caps got a significant upgrade - 4 x 10,000uF industrial grade caps. New industrial-grade ceramic 10% variable trimmer resistors instead of original 20% ones. Fully tuned and singing... I love Rotel sound.

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    Awesome. Glad to see you were able to get it working. Now someone finally gets to enjoy it:) Sounds like you made it "better than new."

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    Quote Originally Posted by PSOVLSK View Post
    Awesome. Glad to see you were able to get it working. Now someone finally gets to enjoy it:) Sounds like you made it "better than new."
    I don't know how it sounded new, although I have a Rotel in my HT. I'll post pics of the upgraded board hopefully tomorrow. Thanks for the amp :)

    Oh, yeah, also put modern 10A-rated bridges in the amp. Modern 10A ones are smaller, faster and more efficient than old 8A-rated.

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    Finally!



    Panasonic PT-AE4000U projector for movies
    EluneVision 92" Cinema Gray fixed screen
    Onkyo TX-SR805 Pre/Pro
    Rotel RMB-1075 Amp
    B&W CDM1-SE fronts
    B&W CDM-CNT center
    B&W CDM1 rears
    Samsung DTB-H260F OTA HDTV tuner
    DUAL NHT SubTwo subwoofers
    Velodyne SMS-1
    Oppo BDP-93 Blu-Ray player
    Belkin PF60 Power Center
    Harmony 890 RF remote
    Panasonic TC-P50G20 TV + PS3 in the living room

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