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Thread: Roland kc 550 wont power on

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    Roland kc 550 wont power on

    Hi my name is Kendrick and I have (2) Roland kc550 amps. And for some reason they will not power on. I've checked all fuses and they are intact (no problem there) I've checked all the boards to the best of my knowledge and found no blown components and I found d no burn outside. Both amps are doing the samething (nothing). The blue led light that indicates power dont light up at all. But I do notice that there is a click sound that come from the speaker when switching from off and then to on, But that's about it! Do anyone have any suggestions!!!!!!

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    Supporting Member nevetslab's Avatar
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    Quote Originally Posted by Kendrick Thomas View Post
    Hi my name is Kendrick and I have (2) Roland kc550 amps. And for some reason they will not power on. I've checked all fuses and they are intact (no problem there) I've checked all the boards to the best of my knowledge and found no blown components and I found d no burn outside. Both amps are doing the samething (nothing). The blue led light that indicates power dont light up at all. But I do notice that there is a click sound that come from the speaker when switching from off and then to on, But that's about it! Do anyone have any suggestions!!!!!!
    Welcome to the Forum! For starters, here's the Service Manual:

    Roland_kc-350_kc-550 copy.pdf

    I haven't located the pilot light in the schematics yet, but, while not digging into the chassis, and going from what's available on the outside of things, (and assuming the power supplies are all intact), none of the signal level outputs are AC coupled, so, you should be able to find mV DC level potentials on Line Out jacks, Headphone Jacks, Stereo Link Output jack, Subwoofer Out jack. You'd see nominal DC levels near 0mV +/-50mV or less. That would be a clue as to whether the bipolar supplies are up and running. Likewise, connecting to the woofer terminals, if the supplies are working (higher DC voltages), you 'd see nominal DC level on the woofer, 0mV +/- 50mV.

    We don't know your skill level, but with nothing working on the KC-550, we start with the power supply, and verify all the proper voltages that run the circuits are present first. I see fuses in the output driver xstr emitter circuits on the power amp, so if either/both are open, you wouldn't get output from the speaker. The Tweeter has a simple RC circuit off the woofer output, so there wouldn't be DC level on it.

    If the preamp/mixer circuits are working, you'd be able to get output from the Stereo Link Output jack from any of the inputs. The Stereo Link Input is a path to the power amp input, allowing you to bypass the mixer/preamp circuits and drive the power amp directly.

    From there, if not getting any results, you're digging further into where the fault(s) are, and we can assist you further when you report back.

    NOTE: Found the LED (LED1)...it's on pg 1 of 4 of the KC-550 schematics...in series with a 2.2k resistor from the +15V supply. NO LED lit could mean you don't have the positive side of the bipolar 15V supplies. If that's the case, you'd be seeing substantial DC offset on the outputs of headphone, line outs, subwoofer out, Stereo Link Out jacks.

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    Last edited by nevetslab; 03-28-2019 at 08:18 PM.
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    What is the line voltage in your country, and are the amps made for that voltage?

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    Hello Kendrick,
    There is a AC fuse in the preamp compartiment. If this one is blown, there is a chance that the rectifier bridge for the power amp is blown. you can check this with rectifier installed because it shortens (at least it was so in my amp). Repair is easy to do because you can cut the leads just under the housing and solder the new rectifier (buy a big one:-) ) to there leads. Don't forget to replace the fuse.
    Good luck and many greetings

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