Sony Active Subwoofer Powers On But no Sound

CesarDRK

Member
2016-03-31 3:21 pm
I have a SA-WMSP85 active subwoofer from sony, and it stopped working recently.
It powers on OK, but no sound is coming out of it.

So i sent it to a repair shop and they asked me about $100 for a fix. Way expensive, so i said no, and the shop invoice described the issue as:
"PARTS: 1x I.C STK 404-130S".

My question is, if the IC is the only issue, i can find it really cheap (like $8) and replace it myself, but should i trust this invoice? Is there i way i can check if the I.C is broke with have-in-my-house-style equipment?

I wanna make sure before i buy the I.C.

This post is with a very similar sub, but with a blown fuse, fixed by the IC replacement. : http://www.diyaudio.com/forums/chip-amps/169477-high-current-fuse-blown-amp-fix-help.html

Thanks in advance!
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Its probably a 95% certainty that the STK is at fault. STK's of all varieties (there are numerous different ones) are a staple of the repair trade.

Data sheet is here,
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You should always check basics such as supply rails and so on. A failed STK may have taken out a fuse or perhaps a safety resistor. A quick look at the Sony service manual would show the circuit and any potential failure items. Look at the application circuit in the data sheet. The Sony will be similar. Notice the 0.22 ohm resistors on pins 12 and 13. Things like that need checking.
 

CesarDRK

Member
2016-03-31 3:21 pm
Thanks for the reply.

The fuse is perfect, no damage at all, the power on light comes on normally.

I noticed something, there is a relay in the circuit. In the past (while the sub worked) when i turned it on, after about 5 seconds i used to hear a "click" and then the sound started. Now, this "click" is not happening anymore. And the day the issue appeared i heard a small "click" before the sound stopped.

Could it be an issue with the relay?
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
The relay is probably in the speaker feed and is used to protect against high DC offset. So it sounds as though that is working correctly and doing its job of keeping the speaker disconnected. When amplifiers fail, the result is often high DC voltage at the amplifier output which would destroy the speaker if it were allowed to be connected.

If you measure the voltage on pins 12 and 13 then you will likely find it is something other than zero (it should be zero).

At this point its very likely that replacing just the STK will fix this. If you do then do not overtighten the screws and use a bit of fresh heatsink compound. Solder braid is good for cleanly desoldering the pins. You could also snip each pin in turn and unsolder them that way.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
:up: sounds like a plan.

Be careful removing the old one. I normally use solder braid for desoldering. Two minutes work to remove an IC like that ;)

Another option would be to snip each wire individually and remove one at a time. Use a piece of stainless wire to run through the hole (solder doesn't stick to stainless) so that the hole and print is clean and undamaged.

Use a smear of fresh heatsink compound on the new IC and do not overtighten it.

:xfingers:
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
If your sub actually runs on those kind of voltages then no common audio chips I know of would be suitable. And I would say there is even less chance of finding a board engineered to be a replacement.

Can you not source the correct replacement chip ?
 
A friend of mine recently gave me a Sony SA-WM500, and it exhibited these same problems. I replaced the STK (In this case an STK440-140S), and the sub came to life. In my excitement, I turned the volume knob up to see how loud things could get. At that point, I heard the DC relay click, and we are once again dead in the waters. I have left unit unplugged, and am once again exhibiting the initial symptoms. Is my specific chip just that fragile, or is there someplace I should look that would be overloading the chip? Thanks!