Amp repair, hopefully. B&K

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SKsolutions
SKsolutions Posts: 1,820
edited August 2008 in DIY, Mods & Tweaks
Got this in the FM. 1 channel was down due to input cable being unplugged during operation. On initial testing, another channel partially let go (No HFreq), but still passes with gain. I'm just opening this up, and am going to give it a go. I've forgotten most of what I once knew, but still remember some of the basics. As far as diag goes, I'm going to begin by measuring what I can against the known good channel (1 good, 2 bad). Fuses check out OK. From there, I'm going to follow the input circuit. Anyone have component level experience with this amp type, or have any knowledge of known issues. . . I'm sure this must be common. Haven't googled yet.
-Ignorance is strength -
Post edited by SKsolutions on
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  • SKsolutions
    SKsolutions Posts: 1,820
    edited August 2008
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    Pic added, can't edit:mad:
    -Ignorance is strength -
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  • ben62670
    ben62670 Posts: 15,969
    edited August 2008
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    Take an ohm meter and read resistance across the legs of the output devices. If they are all the same check the sand cast resistors. They also should be the same.
    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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  • SKsolutions
    SKsolutions Posts: 1,820
    edited August 2008
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    Each ch. has 2 pair of output trannys. I've found one that is stuck/bad/closed. It's Channel 3 which is the completely dead ch. Board reads 1997. Trannys have two different markings, so I'm assuming that they are complementary pairs (2) for each. One reads J162, Japan, the other K1-6H. Look like the old Toshibas.

    The output resistors measure OK within tolerance. Now to find a tranny. I hope Channel 2 isn't a complete ghost. If 1, and 3 get working, I'll be OK with it. If I can't find the issue, I'm going to gift it as a 2ch to a client/friend who's using a POS receiver to power some RS6's.

    Thanks Ben.
    -Ignorance is strength -
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  • ben62670
    ben62670 Posts: 15,969
    edited August 2008
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    Good luck on your parts search.
    Ben
    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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  • SKsolutions
    SKsolutions Posts: 1,820
    edited August 2008
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    Dig key, 7$. New tranny has gate protection diode built in. I believe there is one already on the board, but I don't think it will matter. . .
    Maybe I should order 2 :D
    -Ignorance is strength -
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  • ben62670
    ben62670 Posts: 15,969
    edited August 2008
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    Might not be a bad idea in case there was something that caused the failure.
    Ben
    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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  • disneyjoe7
    disneyjoe7 Posts: 11,435
    edited August 2008
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    An amp could be damaged by not using an input, I heard this before but never believed it can anyone elaborate?

    Speakers
    Carver Amazing Fronts
    CS400i Center
    RT800i's Rears
    Sub Paradigm Servo 15

    Electronics
    Conrad Johnson PV-5 pre-amp
    Parasound Halo A23
    Pioneer 84TXSi AVR
    Pioneer 79Avi DVD
    Sony CX400 CD changer
    Panasonic 42-PX60U Plasma
    WMC Win7 32bit HD DVR


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  • ben62670
    ben62670 Posts: 15,969
    edited August 2008
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    A real simple test you should do is an ohm test from the center of the inputs to the ground of the inputs. Both should be the same.
    Ben
    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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  • disneyjoe7
    disneyjoe7 Posts: 11,435
    edited August 2008
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    Come on Ben answer my question above please!

    A Co-worker brought that Parasound 6 channel amp in the FM to power some A9's and going to use the 5 channel for the center this leaves channel 6 free. Safe to leave open? At least this is what I told him, am I steering him wrong?

    Speakers
    Carver Amazing Fronts
    CS400i Center
    RT800i's Rears
    Sub Paradigm Servo 15

    Electronics
    Conrad Johnson PV-5 pre-amp
    Parasound Halo A23
    Pioneer 84TXSi AVR
    Pioneer 79Avi DVD
    Sony CX400 CD changer
    Panasonic 42-PX60U Plasma
    WMC Win7 32bit HD DVR


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  • MillerLiteScott
    MillerLiteScott Posts: 2,561
    edited August 2008
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    I am only using 4 channels of a 5 channel amp for about 9 months now. I can't see how it would be a problem or hurt the amp. I am all ears.
    I like speakers that are bigger than a small refrigerator but smaller than a big refrigerator:D
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  • Systems
    Systems Posts: 14,873
    edited August 2008
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    disneyjoe7 wrote: »
    An amp could be damaged by not using an input, I heard this before but never believed it can anyone elaborate?
    Not likely,but if an amp has fets in its input stage it might be damaged if an input is plugged or unplugged into it while its powered up.
    Testing
    Testing
    Testing
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  • Systems
    Systems Posts: 14,873
    edited August 2008
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    SKsolutions wrote: »
    New tranny has gate protection diode built in.
    Thats nice, less chance of nuking it with static while handling.:cool:
    Testing
    Testing
    Testing
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  • disneyjoe7
    disneyjoe7 Posts: 11,435
    edited August 2008
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    Thanks for the info :)

    Speakers
    Carver Amazing Fronts
    CS400i Center
    RT800i's Rears
    Sub Paradigm Servo 15

    Electronics
    Conrad Johnson PV-5 pre-amp
    Parasound Halo A23
    Pioneer 84TXSi AVR
    Pioneer 79Avi DVD
    Sony CX400 CD changer
    Panasonic 42-PX60U Plasma
    WMC Win7 32bit HD DVR


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  • Systems
    Systems Posts: 14,873
    edited August 2008
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    I tried to add to previous post but it was beyond 10min.:mad:

    SK if you happen to get 2 new trannys I would replace both.This way they have a better chance of being reaonably matched as they will likely be from the same production batch.If they are not matched they will not share current equally.Also the bias will probably need some tweaking.
    Testing
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  • ben62670
    ben62670 Posts: 15,969
    edited August 2008
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    I'd give you an answer but you already got it on all accounts.
    Ben
    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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  • SKsolutions
    SKsolutions Posts: 1,820
    edited August 2008
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    Thanks for the extra info Ben, & GV. There is a pot on each channel. It's a fairly simple circuit, but the board is double sided, so it doesn't take much to get lost at this point. I hope the tranny will fix this channel but maybe I should have ordered three of them. The trouble will be finding why the HF is rolled off on the other problem channel. Time to get the schem.:D
    -Ignorance is strength -
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  • ben62670
    ben62670 Posts: 15,969
    edited August 2008
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    With the "gain" or "trim" turned all the way up did you get a reading on the input impedance?
    Ben
    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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  • Systems
    Systems Posts: 14,873
    edited August 2008
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    GV#27 wrote: »
    Not likely,but if an amp has fets in its input stage it might be damaged if an input is plugged or unplugged into it while its powered up.

    Common sense tells me to always power down, unplug the cord and go get a snack. Come back and THEN start **** with the connections. My Pioneer 880 in my truck recommends unplugging the battery before moving RCA's from the headunit or the amps. If not you can blow the Pico Fuses/resistors within the unit. I failed to read this part and smoked the fuses. You can't replace them as in just snapping them out and replacing. They are actually on the board as resistors and a **** to get at. Since then I always power down and unplug all my gear before **** with the connections.

    Chuck
    Testing
    Testing
    Testing
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