JBL CSS10 Subwoofer stuck in standby

[Topplok]

Hello, I recently got this subwoofer in a package deal. But I can't seem to get it to come out of standby mode. There is a AUTO/ON switch, but this does not do anything. Tried LFE and Line In but the sub is not turning on from a signal. I have opened it up tried checking for blown caps (not tested) and tested the switch with a multimeter so I know that's not the problem at least, I'm struggling to find answers online for similar symptoms.I'm fairly novice at this so any help would be greatly appreciated.

Also the service manual is available here: https://www.manualslib.com/manual/762091/Jbl-Cinema-Sound-Css10.html?page=2#manual

Chris

 

[Topplok]

 

[restorer-john]

Have a look at the areas I have circled. At least two (the top two) look seriously dry joint issues on the class D power stage, vertically mounted PCB. Those boards are also renowned for failure.

The TIP3x transistors have been running very hot- look at the charred (darkened) PCB and heat stress to their tabs. Test them too or test the +/-15V rails they provide. If the unit is not going from standby to on (red-green), of the front end rails could be out. The PTC also inhibits standby to on, but is unlikely it is at fault. Is the red LED on at all?

The brown glue, has also gone black/dark, which means it is a) corrosive and b) is exhibiting resistive behaviour. I would be attempting to remove it all. If you doubt me, put your DMM on ohms and press the test leads into a contiguous piece of darkend glue- it will have a variable resistance.

I think I even have a Magnat subwoofer here, with exactly the same failed DS1xx module and that was caused by brown glue issues IIRC. I'm pretty sure you can locate those modules on Ali, but it was a year or two ago when I last obtained one.

There is also rust on the various steel parts- the entire subwoofer may have been subjected to moisture ingress.

 

[Topplok]

Hello, thank you for the detailed reply.

Yes the red LED is on, I will try cleaning the entire PCB with IPA and test the Transistors. Found them on Ali for about 2$ each incase I have to change them. How long would it typically for the big caps to discharge? There is no voltage when meassuring right after disconnecting from mains.

It may very well be that there has been some moisture exposure, the guy I got it from has it in a garage.

Chris

 

[AnalogSteph]

The brown glue will have to be tediously scraped away. There's some wire links it covers between the big reservoir caps that I'd be inspecting for corrosion particularly thoroughly. Consider unsoldering one of the caps if you can't reach the spot.