Mackie Thump12 1000-Watt Speaker, Goes up in smoke.

[Benass]

Hello. im trying to figure out why U1(TDA7294v) Goes up in smoke every time I power on the device. ?

Originally U4(TDA8954) Was faulty. Visually had its legs burned.

Got new u4 and also replaced C14 and C8 Caps.


I have +38v and -38v present, and if I disconnect U1 PCB I get LED power on green.

Any one here can read schematics ? and have any ideas ?

Schematics attached.

[petehall347]

Re: Mackie Thump12 1000-Watt Speaker, Goes up in smoke.

check its power supply .also check the speaker for short .

[Benass]

Re: Mackie Thump12 1000-Watt Speaker, Goes up in smoke.

check its power supply .also check the speaker for short .

Speakers not connected.

Could you explain more about power supply?

[petehall347]

Re: Mackie Thump12 1000-Watt Speaker, Goes up in smoke.

check all secondary voltages . dont go near the primary as lethal voltages there .

[eccerr0r]

Re: Mackie Thump12 1000-Watt Speaker, Goes up in smoke.

which legs were burned?

Was this quiescent or did you have an input connected?

Do check all output components for shorts like c6/c18/c1/c10/L13... swapping c8/c14 probably wouldnt do anything, original caps may still have been fine.

[Benass]

Re: Mackie Thump12 1000-Watt Speaker, Goes up in smoke.

which legs were burned?

Was this quiescent or did you have an input connected?

Do check all output components for shorts like c6/c18/c1/c10/L13... swapping c8/c14 probably wouldnt do anything, original caps may still have been fine.

sorry late reply.

pins 17 and 20 which is related to negative 38v rail.

i have a suspition this negative rail blowing u1 chip. im just not smart enight to figure it out.


also c8 and c14 were visualy bulged. thats why i replaced them.

also u4 was burned and shorted. it was preventing entire speaker to power up.
i replaced u4 and now i have green led .

also i have both + and - 38v rails and both +and - 15v rails.

[eccerr0r]

Re: Mackie Thump12 1000-Watt Speaker, Goes up in smoke.

Definitely need to get a DBT on this and stop burning stuff while debugging.

to help me remember what was what, U4 is the LFE driver amplifier in btl mode, U1 is the HF amplifier, and the problem you're having is very very strange as it seems U1 is shorted too.

so what is working and what isn't right now? so it's actually u1 that's smoking not u4?

so originally multiple failure device or did the act of replacing U4 cause U1 to burn?

[Benass]

Re: Mackie Thump12 1000-Watt Speaker, Goes up in smoke.

Definitely need to get a DBT on this and stop burning stuff while debugging.

to help me remember what was what, U4 is the LFE driver amplifier in btl mode, U1 is the HF amplifier, and the problem you're having is very very strange as it seems U1 is shorted too.

so what is working and what isn't right now? so it's actually u1 that's smoking not u4?

so originally multiple failure device or did the act of replacing U4 cause U1 to burn?

Originaly: Device wast'n working. No power.

I disasemble it to find U4 Shorted and burned. U1 was fine(no visual signs of damage)

So I order U4 Chip, and I ordered Hadnfull u1 chips (they were cheap and just in case option)
So replaced U4. Powered on and U1 goes up in smoke.

Disconnected U1 PCB, Powered on and entire power supply up and running (LED is Green)

There is another pcb with Volume control and few other knobs that is not on schematics.



U1 is High F output to the speaker. Feels like volume is maxed out uncontrollably and to much current runs to U1 chip. But I don't know.

It takes 1 second for it to pop. Also, once its burned, PSU protection kicks in and starts cutting power relay fast and Green LED starts blinking with a clicking noise.

[petehall347]

Re: Mackie Thump12 1000-Watt Speaker, Goes up in smoke.

did you buy the chips from a reputable supplier ?

[Benass]

Re: Mackie Thump12 1000-Watt Speaker, Goes up in smoke.

did you buy the chips from a reputable supplier ?

hehe no. aliexpress.

[Benass]

Re: Mackie Thump12 1000-Watt Speaker, Goes up in smoke.

did you buy the chips from a reputable supplier ?

I acquired new chip from Mouser, and it fixed the problem. damn fake ic's from aliexpress.