Car amp fryer of voice coils

[Mooly]

Originally Posted by alsoran

Have removed the other bank of FET's one 540 & one 9540 are showing resistance across the legs and showing zero on the diode test. More on the way - will report back

That means a dead a short (zero on diode test) so maybe it seems more hopeful now.

[alsoran]

To quote a well known scottish band
"let there be light .... and there was light, let there be sound.......and there was sound!!"
FET's did the job - must have replaced the wrong one's first up - can't hurt to have all new ones. Thanks to all who contributed especially Mooly for his patience (again). Will have to be more careful or buy cheap gear so you don't care if it blows up. Hooray!!!

[Mooly]

That's good

[alsoran]

Was positioning the new subwoofer and tried aiming at the back of the rear seat in my car. Turn up the volume - much smoke from the amplifier, I am guessing the resistance to cone movement presented by a confined space and high volume caused this.
So dissapointing, anyway pulled it appart 5/6 power transistors were burned. I replaced these and almost straight away one of the new transistors burned.
My thought is that one or more of the new output transistors has been destroyed. On one pair of the 8 I have resistance across the legs (in circuit), I am guessing this is what is destroying the power transistors. I am tempted to take some of my replaced components (which are still good) and replace the damaged ones to see in principle if this is the problem before destroying more new components. Would this potentially cause more problems? Any assistance appreciated.

[Mooly]

That's a shame.

You are going to have to check them all as before and start again. Hard to see that speaker positioning could cause this tbh... air resistance on it's own and all that.

I think there has to be some underlying cause for this. A first step has to be getting the amp working and then resting into a dummy load for rated output to ensure all is OK.

[alsoran]

Hmmm, replaced 2 output transistors all 6 power transistors - p50n06. Starts up and plays. First time I did this i had a crackle and ominous smell. Amp continued to work. Tried all channels with spare speaker, all's well. Turned on again with no load, crackle and ominous smell, took amp apart again ( did not test to see if it could still play ). Replaced two power transistors showing resistance and failing the diode test. This is where I am now. Should I just try again and keep my fingers crossed. What could be causing this???

[gootee]

Probably caused by not checking _everything_, each time something burns.

[Mooly]

There has to be some underlying cause. Just replacing devices and hoping isn't going to work.