Subwoofer problem Mackie swa 1801

[ri23c]

Hello everyone, I have a problem with the active subwoofer Mackie swa1801. The problem is this: I turned on the sub that for many months, and I turned on not raising the volume from my phone lights up the led thermal. Viewing manual means that the temperature exceeds 60 degrees, and should also go mute but feels the same but I had just turned on. I disassembled the amplifier and I noticed first by the smell of something hot and then I had confirmed with my finger that I burned by touching the resistance r65.Prima I became aware of the resistance I raised the pot that's on panel and (do not know why I did it), the red led is lit thermal altogether and burned the transistor q12 . the transformer is not original because I took the sub used and that the former owner had changed with a more powerful (if you do not know what he meant with more tension hope not or higher amperage) because it was burned. Before I realized the problem I noticed a sound distortion. What could it be?
Sorry if the text is not particularly spelled it right because I'm Italian and I do not know much English.

[Jazz P Bass]

It sounds to me like U3 is faulty.

Agilent (Hewlett-Packard) - datasheet pdf

And possibly also Q14.

[ri23c]

Thank when I changed them and tried do you know

[ri23c]

The components that take new must be the same brand of those mounted or can be of different brand?

[Jazz P Bass]

As long as the datsheet particulars for the original component are met, 'brand' does not matter.

To be sure, Iwould replace both U1 & U3 & the power mosfets Q6 & Q14.
Also. seeing that Q12 took a hit, it may be wise to aqlso replace Q9.

Mackie_SWA1801_Amp_sch.zip

[ri23c]

I'll let you know.

[ri23c]

I noticed that the mosfet q6 & q14 are mounted IRF540N, but the schema is written IRF540. it is better to take the mosfet that holds more amps or the original as in the diagram?

[ri23c]

Looking at the datasheet I've seen that the MOSFET mounted on the board that is IRF540N has Rds (on) of 44mΩ rather than schema is Rds (on) of 0.077Ω. Which mosfet use ??

[Jazz P Bass]

I would go with the IRF540N.

[ri23c]

OK thanks
I also noticed that the c2 & c capacitors 34 are mounted on schda 100v instead in the scheme are to 63v. I keep those to 100v?

[ri23c]

Does anyone know the output voltages of the original transformer? And the amperage

[ri23c]

Removing the card has torn the insulation. I put the insulating mica or silicone?

[ri23c]

I changed U3, U1, Q6, Q9 and Q14. amplifier wake there is always the R65 resistance that heats more than r1. I noticed a distortion when I turned up the volume before you turn on the LED thermal. I forgot to tell you, that when I disassembled the amplifier from the rest of the subwoofer, I noticed that a transistor (Q5) of the final did not touch the heat sink. It could be the one causing the problem?

[ri23c]

I solved the problem of transistor q12 that continued to burn. When I turned on the amp I measured the voltage from f1 and f4 fuses which is 35v but drops to 34V when I put the music. I still have the problem of the thermal LED that lights up when I exceed a certain volume of sole and r65 resistance warms much more than r1. What can be, I checked all the transistors and diodes on the board and they are all good. It could be u3?

[g1]

Tell us what the issue was with Q12, maybe it will serve as a clue.