SVS Sledge STA-1000D amplified sub dead

[JP-Stereo]

Hi, i have a dead SVS Sledge STA-1000D amplified sub.
The internal SMPS and Class-D bloc amplifier is receiving AC but give no life sign.

This SMPS & Amp bloc is made by Formosa-Audio.
Model FMA-99051 v: 4.1
I am currently searching for the schematic.



No apparent component damage but i found this on the reverse side of the board :



Is it normal or something is arcing ?

And, where can we found these grey hoodies ?

Thanks.

[The Dude]

Hard to tell for sure from the pic, but it looks like possibly heat sink compound, which shouldn't be a problem. Those are likely the FET's for the switching supply. Are either shorted?

[JP-Stereo]

Hi, it was a powdery stuff, easy to clean with alcool.
Kind of dust attracted by the static field of the high voltage.
On the right side transistors, the varnish was burned like if there was some sparking.
I will try it again as it is clean now.

I also found the current model of this amp, it's Formosa Audiomate HD-11024BD.

[JP-Stereo]

Nothing short there.
Since i also redo a few solder, i am not cerain what it was but now the +5/-5 volts bus is alive.
I will test with the preamp.

[JP-Stereo]

No sign of life even with the preamp plugged but i made a few other find...

No schematics, most original IC part numbers are erased and replaced with a clueless proprietary ID...
This one is special.

The +/- 5vdc rails are fine at the preamp connector (CN1).
The preamp's display don't come alive, no sign of life anywhere.

The firsts rectified supply rails are at +159vdc / -170vdc at the first capacitor bank.
That's before the IGBT, after the IGBT there is only a steady +159vdc rms.

U101 has no supply, it's supposed to come from Q104.
It's a kind of soft start circuit.
Q104 is fed by R133 through D110 from the Supply isolation transformer.
Q104 is triggered by U105 through R134 wich is regulated/clamped by D115 a Zenner.


U105 is an optoisolator mounted on the other side of the board.


No signal at the output pin 3 (green star), but the following signal at the input pin 1 (lite green star).



The D115 clamping diode test ok.
R134 is fine.
The base of Q104 is at 4 meg ohm from ground.
Q104 is not suspect yet since it doesn't have it's starting signal...
Should i remove R134 to check if there is to much load on U105 output or it's pretty obvious that it is U105 by now ?

At least U105 had it's original marking and is still available, just ordered a few.
I really hope that Q104 is OK because it's marking lead to hundreds of results...


Without a drive from U101 is it normal that the IGBTs output line fully pass the positive rail ?

[JP-Stereo]

I just install a new optoisolator (U105) , but still no ouput from this opto (to R134)...

I've removed Q104, measured, then also removed D115, measured, followed by R134, still no signal out of the opto even if this side of the line is now unloaded.
It's not grounded or loaded in any way, so the signal should appear at R134
But if i put the scope to 100mV/div there is something, but so weak (80mv) and the line is still totally unloaded.
Can this be a signal: Input= Yellow is the anode, Output= Blue is the emitter



Those SVS amps were very popular and expensive units.
I begin to think about a reversing operation..
But i have the feeling that someone have already a lot of this work done.

From what i've seen SVS have about 2 generic model of amps that may receive different power components.

[simka]

Hi, i have a dead SVS Sledge STA-1000D amplified sub.
The internal SMPS and Class-D bloc amplifier is receiving AC but give no life sign.

This SMPS & Amp bloc is made by Formosa-Audio.
Model FMA-99051 v: 4.1
I am currently searching for the schematic.



No apparent component damage but i found this on the reverse side of the board :



Is it normal or something is arcing ?

And, where can we found these grey hoodies ?

Thanks.

Hey! It sounds like you’ve got a tricky situation with your SVS Sledge STA-1000D. The fact that the SMPS and Class-D amplifier are receiving AC but aren’t showing any signs of life could mean there’s an issue with the internal components, such as a blown fuse, damaged capacitor, or something more serious like a short circuit. It's not normal for it to just stay dead, so definitely worth checking for arcing or any visible damage.