I Need Help to repair me RCF art 312-A MK 2 Speaker

[Bernhard95]

Hi Guys,

I hope any one can help my to repair my RCF art 312-A MK 2 Speaker

That's the issue:

If i switch it on with no xlr connected and set the volume to minimum it makes a loud noise.

If i uper the volium the noise will be silent.

If i touch the Volume switch i will here also a loud noise, this occur in all volume switch positions.

On the circuit board some transistors looking like overheated.
Photo: https://ibb.co/yVJR8Sy

After cleaning them they looks not damaged.

Also the cooling plade will be extremely hot after not more than one minute power on.

I think there goes something wrong in the preamp.

It is mutch over sensitive.

To any one have an idea what is damaged here?

maybe someone has the schematic for the speaker?



Thanks for your help

[The Dude]

Here's a download link for the "non-MK2" version. Maybe it will be similar enough?

https://elektrotanya.com/rcf_art312a.../download.html

[Bernhard95]

Thanks The Dude, I have found the MK1 Schematic before, but mk1 and mk2 have not the same AMP Mainboard.

-

If anyone has a replacement board for sale, I would be also interested. Complete Amplifier or only the mainboard

[J M Fahey]

Hi Guys,

I hope any one can help my to repair my RCF art 312-A MK 2 Speaker

That's the issue:

If i switch it on with no xlr connected and set the volume to minimum it makes a loud noise.

If i uper the volium the noise will be silent.

If i touch the Volume switch i will here also a loud noise, this occur in all volume switch positions.

On the circuit board some transistors looking like overheated.
Photo: https://ibb.co/yVJR8Sy

After cleaning them they looks not damaged.

Also the cooling plade will be extremely hot after not more than one minute power on.

I think there goes something wrong in the preamp.

It is mutch over sensitive.

To any one have an idea what is damaged here?

maybe someone has the schematic for the speaker?



Thanks for your help

I think all that points to a cracked/broken track or solder pad at or near the volume potentiometer (not sure what you mean by volume switch, is it the potentiometer?)

A broken ground track would set volume to "always maximum", "very sensitive" , it could also make amplifier oscillate, maybe at high frequency so inaudible, but strong enough to overheat power amp even if apparently "silent".

maybe you refer to a sensitivity switch, selecting microphone level or speaker level input; if broken, or broken tracks around it, it will also lead to extreme sensitivity and possible oscillation.

Broken/cracked tracks or solder will often be intermittent, also explaining sudden unexplained volume variations.

I suggest you check input module board, look at it under good light, using a loupe or strong glasses (I use +4 diopter reading glasses) and search for tiny cracks, maybe reviving solder helps, but sometimes the crack is on the track itself, hidden by solder mask.

It does not look like a power amplifier transistor problem.

[Bernhard95]

I think all that points to a cracked/broken track or solder pad at or near the volume potentiometer (not sure what you mean by volume switch, is it the potentiometer?)

A broken ground track would set volume to "always maximum", "very sensitive" , it could also make amplifier oscillate, maybe at high frequency so inaudible, but strong enough to overheat power amp even if apparently "silent".

maybe you refer to a sensitivity switch, selecting microphone level or speaker level input; if broken, or broken tracks around it, it will also lead to extreme sensitivity and possible oscillation.

Broken/cracked tracks or solder will often be intermittent, also explaining sudden unexplained volume variations.

I suggest you check input module board, look at it under good light, using a loupe or strong glasses (I use +4 diopter reading glasses) and search for tiny cracks, maybe reviving solder helps, but sometimes the crack is on the track itself, hidden by solder mask.

It does not look like a power amplifier transistor problem.

Thanks J M Fahey,

Yes I mean the volume potentiometer.

I have already check the tracks and the solder Points, but I will double check it this und I will re-solder the suspicious solder joints around the potentiometer.

If this will not help I will solder an new potentiometer in, maybe this is broken.

[paleeman]

You have two problems to solve: 1. The noise problem - is present because of a faulty/dirty volume potentiometer. Try cleaning it with Deoxit, or replace it, if you can find a spare. 2. The extreme overheating - You have to check the idle current. Measuring at the test points, the value should be around 8mV DC. If adjustments need to be made, do it with TRIM2, but be careful with the trim pot, because the trim pot itself can be faulty.