RCF ART315A Protect mode

[diydidi]

Hi All!
I have this unit for repair. The red "LIM PROT" Led stays on after power up. Both hi and low amps are muted. I have already checked all outputs SAP16N/P, as well as the mosfets that switch the HV+/- rails. All voltages of power supply are good. Also +/- 12 volt supply is good, and the 5,5v is also good!!
Any ideas??

[mozwell]

There is a mute line going into the power amp. This seems to originate from teh filter card, and NE5517.
There is also another mute command from the power amp, from the two fuses, are these fuses intact.
While power is off, check output transistors for shorts.

Do all speaker outputs measure 0VDC, there are no speaker relays, so the may use the MUTE command for turn on / off de thumping.

[diydidi]

Mozwell. I've already checked all things you mentioned.

[mozwell]

Lets find out if it is the mute lines, or some other problem.
Are the mute lines high, or low, what are the outputs of U12, is NTC pad (J1 & J2 connected).
If you temporarily remove R117, (on the mute line for the HF amp) does the HF amp give output.
If you short B-E of Q10 does the LF amp give output.
Lift one end of D23, does this help ?
Is the unit set to "line", (sw3)

Check U8, are the +/-5V supplies ok, if IN is high, no channel is selected.

Check the volts on R96, R97, are these ok, these go to the "filter pcb" & U5, if you lift one end of R25 does this help.

As with any repair, first check the fuses, power supplies, any DC on the output, & check the power transistors for shorts.
If all of these are ok, inject an AC signal to the input & follow it through each stage in the amp to find where you dont get what you expect...... a 50mV 1kHz signal shoudl be ok.

[diydidi]

Here are my findings:
U12 Pin1&7: 4VDC
Cathode of D23: 3,7VDC
Mute Cmd line: 10,92VDC
Filter card ready line: 11,64VDC
VR107: 1,1VDC
U15 pin2: 3,56VDC
U15 pin3: 5,8VDC
Low out: 0VDC
I already replaced U15. No change. The next thing i'm gonna do is replace U12. Anything I'm missing??

[paleeman]

Change the MMBTA 42 and MMBTA 92 transistors (SMD, marked 1D an 2D), most of these fault come from them.

[diydidi]

Change the MMBTA 42 and MMBTA 92 transistors (SMD, marked 1D an 2D), most of these fault come from them.

Hi Paleeman! Thanx for your reply!! Do you know this for a fact? Have you experience with these units?

[paleeman]

Hi.
Trust me, 310As,312As, infact all the Art series , suffer from this problem (sooner or later), the unusual behaviour is caused by one or two of these transistors, but I urge you to replace all of them (3x MMBTA42s and 3xMMBTA92s). BTW, I spent couple of sleepless nights trying to figure out what's wrong (and now I am glad to help somebody :-) ) .One advice, when you replace the transistors, be careful while you desolder them, because they are glued to the PCB. (nothing new )

[diydidi]

Paleeman! I did as you suggested. No luck. Prot/lim led stays on. Any other ideas??

[paleeman]

Sorry, Diydidi, if you have replaced all 6 transistors and you still have prot-light on, then I can only assume that you have checked the other 20 things that I can come up with now. The best thing would be to determine whether you have true fault (DC on output, etc) or just the protect circuit is messing with you (usually the case). Now, what I would do is, disconnect the mute/protect line (I belive Mozwell suggested that too), and try to figure out if the LF and HF amps are OK. If so, you may have an error on the filter card...

[diydidi]

Both amps drive well with mute/protect disconnected. so I reckon it must be filter card then.....

[paleeman]

One more thing, can you change the EQ? By each press you'll have to be able to alternate between the 3 presets, even with PROT on. If you can't, the the fault can be in the control circuitry.

[diydidi]

The person that brought this unit for repair only brought in the amp unit itself. I don't have the speaker enclosure with those Led's in the front. Can it be that this fault I'm getting is due to the front Led board not being connected??? Maybe i managed to solve the problem, but because its not connected to those led's, im getting error?????

[diydidi]

Ok I checked with multimeter the led outs on connector J3X: When switched there 3 states. Both lines are high. Then one line by itself. then other line by itself.
So I presume it is switching Led's on font panel. this is assuming the front panel has a Tri-colour LED?

[paleeman]

You assume right, it has either green or red or the both of them lit. Unfortunately you don't need them to operate the AMP. But, hey, it's good news if they react, 'cause, now at least you know that the PIC12F629 is "alive".