RCF Art300A

[skint]

Thank you for replying g-one. I took the control board from the faulty monitor and connected it to the good one and regardless of what position the switches were at,this control board performed exactly the same as the other.(no problem with volume in good monitor with any of the panels)
Connecting the control board from the good monitor into the faulty one made no difference to it.The volume was still lower with no switches pressed in,or voice or music switches pressed in.
The only way both monitors were equal volume was when the line/micro switch was pushed in.This makes the monitors very loud with hiss even at low volume when used with a mixer.
The difference in volume occurs when either no switches are pressed in,voice switch in ,or music switch pressed in.
Having both voice and music both pressed in together also doesn't cure the volume difference.
I hope you can understand my description. thank you

[Jazz P Bass]

So the problem is in the power amp.
Something is strange about the Hi / Low power amp inputs.
The inputs are labeled Hi & Low but the output from the front panel simply says Out 1.
Is there a crossover?

[g1]

I took the control board from the faulty monitor and connected it to the good one and regardless of what position the switches were at,this control board performed exactly the same as the other.

The only way both monitors were equal volume was when the line/micro switch was pushed in.This makes the monitors very loud with hiss even at low volume when used with a mixer.

I think what you are saying is if the good monitor has the line/micro switch out, and the bad monitor has the line/micro switch IN, then they are the same volume.
If the line/micro switch is pushed IN on BOTH monitors, then the bad monitor should still be weak. To me, this is the only way it can make sense.

[skint]

Hi g-one. Strange as it may seem, if the line/micro switch is pushed IN on BOTH monitors and the volume set the SAME on BOTH they both sound exactly the same volume.
I plugged a microphone directly into the line/micro input and with the line/micro switch in,both monitors sounded exactly the same volume and clarity,but this setting doesn't work well when using a mixer.
It is when either NO switches, MUSIC,or VOICE switches are pushed in that the difference in volume occurs. The volume of the good monitor set around half way on and the weak one full on to have both at equal volume
I know it seems hard to understand but that is what is happening. thank you

[g1]

The reason I'm not able to understand is because when you try both control boards (set to line position) in the good monitor, you said there is no difference in the volume level.
But I'm getting stuck on this and impeding progress in this thread, so I will let others continue on, and I will try to stop interrupting.

[skint]

g-one. I really appreciate the effort you are giving to my problem and it is probably my fault due to my limited knowledge for not being able to explain correctly what is going on.
The problem does not seem to be coming from the small control panel as it makes no difference whatsoever which of the two small control panels or what position the switches are at,they BOTH sound the same volume and work the very same when plugged into the GOOD monitor main board.
When ANY of the two control panels are plugged into the FAULTY monitor main board,the volume of it is much lower than the good monitor in every position EXCEPT when line/micro switch is pressed in.(then both monitors have equal volume but very loud)

[J M Fahey]

Skint, you still haven't answered my questions from post #26 , 10 posts behind.

[Jazz P Bass]

At the risk of repeating myself, there is something wrong in the power amp.
Now what.
I don't know why we are beating this thing to death.
Take the thing to somebody that knows what they are doing.
The troubleshooting that you did is more than the last repairers did, so you are ahead of the game.

[J M Fahey]

Pity but I think we are real close, problem is skint , who is our eyes there, does not look where we are asking him to.

[plec.22]

Evening all, I've worked on these biamped speakers before and noticed how they use a ic amp to drive the high end and one pair of o/ps to drive the bass speaker also the ht rail is about 80v on them o/ps to the bass amplifier. The faults these units had was total dead with blacked fuse and burnt drivers plus s/c main power transformer so after replacement of parts to amplifiers with o/ps devices and ic's etc they worked well enough, the only mod I added was to fit a fan plus thermal cut out just in case things cooked up again.

some of the smd's can be tricky to rework such as op-amp's and track tracing over the double sided pcb.