Tweet
Okay, have a Momark 800, that uses two IRFP264 mosfets with one of the output filter coils overheating.
It melted C86 which I believe is .68uf and also the .33uf connected to the 4.7ohm 5w section of the filter, that was bad.
I replaced all the damaged/bad caps, tested the others in the output section and the larger coil is still overheating.
It's not as bad, and the high frequency oscillator level is lower than it was before on the output
On the one end of the coil that's overheating the high freq signal is about 220Khz at about 200v peak to peak
The other side hi freq is the same level as the output signal, it goes through the 2nd coil, the two 1ohm 5w resistors then to the output relay.
There's about 1v DC on the hot coil, is it possible a leaky FET could be causing it to overheat?
I tried another coil close to the originals' value of about 15uH, it also gets hot
I was referencing this informative post by Greg Robinson from the Markbass thread below
Thanks
"Sorry for the necropost, but I just repaired A CMD 102P (same amplifier, different speakers in the combo) with the same fault. Figured here was as good as anywhere for posterity.
At least in my case, C86 - 680nF 400V failed first, causing R53 and R54 (4R7 5W) to overheat, leading to C87 (330nF 250V) and C88 (100nF 400V) melting, as they are right next to each other.
All these components, along with L2 and L10, form the class D output filter. L2 and C86 form the first pole, L10 and C88 form the second, and C87 is in series with the parallel pair of R53/54 to form a Boucherot cell/Zobel network. Without C86 to work with L2 to do the bulk of the filtering, R53/54 overheat, with escaped magic smoke and extreme EMI emission being the result."
It melted C86 which I believe is .68uf and also the .33uf connected to the 4.7ohm 5w section of the filter, that was bad.
I replaced all the damaged/bad caps, tested the others in the output section and the larger coil is still overheating.
It's not as bad, and the high frequency oscillator level is lower than it was before on the output
On the one end of the coil that's overheating the high freq signal is about 220Khz at about 200v peak to peak
The other side hi freq is the same level as the output signal, it goes through the 2nd coil, the two 1ohm 5w resistors then to the output relay.
There's about 1v DC on the hot coil, is it possible a leaky FET could be causing it to overheat?
I tried another coil close to the originals' value of about 15uH, it also gets hot
I was referencing this informative post by Greg Robinson from the Markbass thread below
Thanks
"Sorry for the necropost, but I just repaired A CMD 102P (same amplifier, different speakers in the combo) with the same fault. Figured here was as good as anywhere for posterity.
At least in my case, C86 - 680nF 400V failed first, causing R53 and R54 (4R7 5W) to overheat, leading to C87 (330nF 250V) and C88 (100nF 400V) melting, as they are right next to each other.
All these components, along with L2 and L10, form the class D output filter. L2 and C86 form the first pole, L10 and C88 form the second, and C87 is in series with the parallel pair of R53/54 to form a Boucherot cell/Zobel network. Without C86 to work with L2 to do the bulk of the filtering, R53/54 overheat, with escaped magic smoke and extreme EMI emission being the result."
Comment