Good morning everyone ! I'm repairing a RCF ART -710A MK2 ! In the treble amplification part it uses a class D module and has IRFB4229 as final mosfet and IRS20955 as driver which I replaced with IRS20957!
Now I have this problem! When turned on everything seems to work but after a few seconds checking the waveform on the gates of the mosfets I have an inaccurate square wave of different amplitude, to then turn off as if the driver went into protection!Is it possible that between the 2 drivers I have to replace resistive values or does it require different values for example on the OCSET and VREF pins?
Now I have this problem! When turned on everything seems to work but after a few seconds checking the waveform on the gates of the mosfets I have an inaccurate square wave of different amplitude, to then turn off as if the driver went into protection!Is it possible that between the 2 drivers I have to replace resistive values or does it require different values for example on the OCSET and VREF pins?
Attachments
Good morning ! unfortunately in the last tests I had problems with the triangular wave signal generated by 2 integrated MC33078 ! I no longer have the triangular signal and therefore if I try to connect the output mosfets they fail immediately! unfortunately I could not find the diagram of this product!
does anyone have the diagram of the ART 710 A MK2?
does anyone have the diagram of the ART 710 A MK2?
Triangular waves are usually generated at two stage opamp oscillator. One is an analog integrator and the other a Schmitt comparator. The triangle is thus compared with audio signal to generate rectangular waves at fixed frequency and variable duty cycle.
Until you have no good triangle waves, don't sit final MOSFET's.
Two common triangle generators.
Until you have no good triangle waves, don't sit final MOSFET's.
Two common triangle generators.
Attachments
Last edited:
Good morning everyone ! Finally I managed to restart the amplifier ! I noticed that at the beginning as soon as I turned it on it worked for about 30 seconds but I noticed an overheating of the mosfets! At this point I inserted a 22k resistor between the gate and the source of the mosfets to force the mosfets to turn off and then I did some tests by changing the resistive ratio which modifies the DT of the IRS20957! now the amplifier works but in my opinion it was essential to add the 22k resistor because evidently the project does not include an additional driver able to properly drive mosfets that require a considerable gate current! So I tried inserting a 4.7ohm gate resistor and a 22k resistor between the gate and the sources of the 2 mosfets and now it works stably!
Buenas tardes Osvaldo, necesito hacerte una consulta, estoy trabajando en España, me podrías ayudar. Escribime por WhatsApp. Muchas gracias. 0034643506317. Fabián.
Last edited by a moderator:
Do not run class d amps with no load !
Some stop oscillating and others just put a few volts DC on the output.
And some run ok but can have high volts on output due to output filter ringing.
One year ago I repaired a D-class (db Technologies Opera 512DX) with blown output filter coils. When I tried it (without loudspeakers) I detected 25V in both tweeter and woofer outputs, so I thought that something was still bad. I confess that I checked many things and found nothing wrong, but I refused to try it with speakers connected, because I knew that means killing them. Eventually I gave up with that repair.
Today I’ve read your post for another reason and that case has come again to my mind. I picked it up again, connected speakers, tried it and it works. I feel ridiculous, but at least happy to have fixed this one. Coils still get hot, but that’s another story...