RCF Art300A

[skint]

Hi everyone.I have just joined and I apologize if this question has already been covered
I have two RCF Art300A powered speakers and recently one of them has lost about a third of its output power (I have to turn up the output on my mixer much higher on this speakers output to balance the volume of both speakers) The sound is still perfectly clear with this speaker.Only the volume has got lower. I have cleaned all connections and swopped the small control panel on the back but no difference
I would very much appreciate any help from fellow members..Thank you

[Enzo]

May I assume you have the mic/line selector switch in th appropriate position? That would knock your levels down.


But assuming the problem is inside...

The schematics are at Elektrotanya, maybe elsewhere too. Get them if you have not already.

This speaker has separate power amps for woofer and tweeter. Are BOTH those drivers diminished? Or maybe just the woofer? Or could the tweeter sound be missing completely? Without the horn running, a speaker will sound a lot less loud.

Both amps appear to have fuses, check those.

Also, the preamp, which you apparently swapped with another speaker, needs +15v and -15v to operate properly. Make sure that both those are getting to that preamp board.

[skint]

Thank you Enzo for replying .The mic/line switch is always set to music on both speakers as I use these for both mic and keyboard Both the woofer and tweeter have lost power.I have checked fuses inside and they are ok. The panel I switched is the small one on the back with the mic input/output and mic/line settings.(I swopped this from the other idencial speaker that is going perfect). When you listen close,the sound seems to be far back in the speaker compared to the other one,but there is no distortion or rattles.
I checked the voltage that you suggested and it seems ok 14.73v and14.58v ( i am not a very experienced at this)

[The Dude]

Many times when people describe the sound as something like "far back in the speaker" it is broken/shifted magnets on the speakers/drivers themselves . I'd start by popping the grill and seeing if the speaker cone moves freely. Was the speaker dropped?

[skint]

RCF Art300A

Many times when people describe the sound as something like "far back in the speaker" it is broken/shifted magnets on the speakers/drivers themselves . I'd start by popping the grill and seeing if the speaker cone moves freely. Was the speaker dropped?

Thank you Dude. I have changed the amplifier part in the back with the one from my other speaker and the problem seems to be in that part,The speaker and tweeter works perfect with that one.
Both woofer and tweeter have lost about 1/3 power when listened to side by side with the other one but is still clear sounding

[olddawg]

I have seen a common, recurrent problem with many other brands of these types of powered monitors. They underrate the voltage spec for the power supply filter capacitors (usually 4700uf @16v) so they eventually fail. Usually they dome up and can be identified by visual inspection. The boards though are normally double sided and the caps are usually incased in silicon glue so... It's an easy fix if you have the skills, a potential nightmare if you don't. I'm not saying this is definitely your problem, I don't have it on my bench. But I have seen it a lot.

[skint]

Thanks for taking time to reply olddawg Your answer could very well be the cause of my problem as I believe there are two amps in these monitors and both of them seem to be affected as neither woofer nor tweeter sound nearly as loud as my other idencial monitor. I will let you what the outcome is

[Enzo]

SO you changed out BOTH the preamp module (jack board) AND the power amp module?

[skint]

I swopped the small panel from my other good monitor (with RCA and line in switches)and it made no difference to the volume.
I swopped the complete main panel board today from my other good monitor, to check the woofer and tweeter of the low volume one and everything worked ok and volume was up to normal, so the problem seems to lie somewhere in the main panel as I then tried the faulty main board into the other monitor and the volume was much lower in it than the original one.
Thank you for your interest.

[Enzo]

Fair enough then.

SInce the tweeter and woofer each have their own amplifier and you are reporting that both drivers are affected by this (right?) we need to look first at things they have in common. The schematic I have is four pages, the preamp board, the two power amps, and the power supply. Is that what you have or do you have more? What I do not see is the crossover. What splits the signal into highs and lows for the two amps. That part would be suspect. But within what I can see, the first suspects are the two channel mutes, Q37 Q38 on the power supply page lower left. They shunt the signal in each power amp right after the input op amp. If those are stuck on or faulty, they could leave your amps attenuated. Check if there is voltage on their gates. JFETs are normally ON until turned OFF with a gate voltage. You can also measure their resistance while the circuit is livem and hope to find it not a low value.

[The Dude]

rcf_art300a_sch.pdf

I'd start by checking your rail voltages right off of the bridge rectifiers. That'll tell you if your filter caps are bad or not.

[Enzo]

Oh foo, that is the copy I have, I was hoping to see the crossover stages.

[The Dude]

Sorry to bust in on your post Enzo. Looks like we were both typing at the same time. My intent is certainly not to get in the way here. Much respect.

[Enzo]

I don't think you are in the way, the more people contributing the better. I was just hoping you had a different schematic file that included what mine leaves out.

[skint]

Thanks very much to everyone for their help. I will not have time until Tuesday to check board. I don't have any info either on the crossovers.I will post the results of tests here when completed.