Members Adey Posted October 25, 2018 Members Share Posted October 25, 2018 Hi there. The singer in our band has a Laney XCP-112 active monitor that we'd like to use. The only problem is that some time ago someone borrowed it, and fed it a powered signal, and since then it has no sound coming from it. I take out the woofer, and sure enough there is no impedance reading with a DMM, also when i (gently) push the cone I can hear it scratching. Also the tweeter shows no reading either, so im 99% sure that both coils in the drivers are toast. We have sourced replacement drivers (from Laney) but before we spend money, we'd like to be certain that the amp itself is still working. The woofer is an 8ohm speaker and as far as I can tell is wired in series with the tweeter via a crossover. So based on my (limited) guitar amp knowledge, I assumed that both speakers would be 8 ohms, and being that they are wired in series would create a 16 Ohm load. So, I install my 16 Ohm Celestion G12T-66 directly to the amp outputs (bypassing the crossover) and turned all dials down to zero, and plugged in a mic. As soon as I turn the monitor on I get a LOUD hum! Almost as if the monitor was being fed a 50hz signal from a signal generator, a pure sine wave if you will. This was not just typical background hum. Would this indicate a problem with the amp, or was my method of diagnosis just dumb and folish? I'm prepared for the latter Any other sensible way of testing the amp without blowing it or myself up? Many thanks! Link to comment Share on other sites More sharing options...
Members WRGKMC Posted October 26, 2018 Members Share Posted October 26, 2018 The power head is blown. Its power transistors are shorted and it passing 110V AC directly to the speakers I should also note your assessment about it being a 16 ohm amp is bogus too. If this monitor has a woofer and tweeter, its likely got either an active or passive crossover. Its likely to be a 4 or 8 ohm head, not 16. The crossover provides the impedance and splits the frequencies to the speakers. Seeing your power head and speakers are both blown I'd suggest you buy a new monitor vs trying to repair this one.you can probably find a used one in working condition that is far lower in cost then it takes to repair this one. Even a new one on sale is likely cheaper. Your assessment that the monitor was fed a speaker signal is questionable too. If the amp was fed a speaker signal it should have blown the front end line preamp, not the back end power amp and speakers. I suppose it could have gotten past the front end and blown the entire thing depending on the design and the ignorance of the users in failing to recognize they were damaging it. My advice don't throw good money after bad. If you happen to come across an extra speaker you could gut the thing and make it into a passive monitor I suppose. Getting the amp and speakers repaired/replaced will most likely cost more then just buying another active monitor. Several companies make them as low as $100 these days. Link to comment Share on other sites More sharing options...
Members Adey Posted October 26, 2018 Author Members Share Posted October 26, 2018 The "being fed a powered signal" was just what our singer said to me, but I see what you mean, it makes sense.My thought would be to try and find a used one for around £100 like you said. But our singer reckons they are hard to find locally and most sellers prefer to do cash on collecion, and are reluctant to post monitors due to the size and weight. We are toying with the idea of convert it into a passive speaker also, so maybe we'll end up going that route. Thank you for your input on this, its greatly appreciated. Cheers 👍 Link to comment Share on other sites More sharing options...
Members onelife Posted October 29, 2018 Members Share Posted October 29, 2018 FYI... if the woofer, tweeter and capacitor were wired in series then the high pass filter (capacitor) would would prevent low frequencies from passing through the woofer as well as the tweeter. Link to comment Share on other sites More sharing options...
Moderators isaac42 Posted October 29, 2018 Moderators Share Posted October 29, 2018 Could be, though there are series crossovers. I'd be a little surprised if they went that route. Link to comment Share on other sites More sharing options...
Members onelife Posted October 30, 2018 Members Share Posted October 30, 2018 interesting - using shunts instead of a parallel circuit i wonder what the adventage of would be Link to comment Share on other sites More sharing options...
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