Infinity PS-12 Powered Subwoofer Fired Amplifier

[ben7]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

I'm pretty sure it's the dubstep (what's that?).
Is that that dance that Popcorn does on the show Moonshiners?

It only "crackles" when it hits really hard. So, I'm assuming it's bottoming out.
But it never hurts to double check the solder joints.

I'll look for a 6.8uf 100v radial NP. If I can't find one I just might try an axial.

It could be that it needs to be vibrated very hard to make the [possible] bad solder joint disconnect/reconnect.

When a speaker is bottoming out, it will sound like a muffled 'brrrrr' 'brrrrrr'; a bad solder joint causing an interruption in a signal path would make the speaker produce a sharp crack or pop sound.

[hardwareguy]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

If this amp dies again, make sure the muting and modulator power supplies are up.

The large power resistors feeding the small regs off of the main rails are undersized on a few of these. JBL/Harman specifies a 3W and a 5W resistor but some units have a 1W and a 3W respectively. These overheat the board leading to some SMD transistors nearby to fail outright or become leaky.

The traces will be visibly discolored and the solder joints at the resistors will be in poor condition.

The service manual for the JBL-E250 and PB12 covers this amplifier. You have the Revision 2 board. (rev. 1 uses a very nasty hybrid module and isnt really worth fixing!)

[budm]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

Yeah, the JBL uses that crappy ClassD module in PB-10/12. I mod a couple of them with free sample power amp IC from National/TI instead.
http://s807.photobucket.com/albums/y...20PB-12%20mod/

[Beretta6888]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

I have the same problem with the capacitor but my circuit board has burned much worse than the first posts. Is there just the one capacitor or is there a very small resistor or cap on the bottom of the circuit board next to where the faulty cap is connected? Also can anyone give a link of where to find the capacitor needed, the link in an earlier post doesn't come up with the same specs.

[999999999]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

^ See the picture linked originally, and below, there is nothing directly under the capacitor but between the solder pads for it and the outermost screw securing the heatsink, there are a pair of diodes and resistors on the back of the board.

Also moving away from the heatsink, left in the picture towards the edge of the board, there's one cap, then an inductor, then a 2nd cap on top of the board. That second cap does have a chips capacitor on the back of the board situated between it and the inductor.

[Beretta6888]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

Okay thanks, just making sure there isn't anything else like one of those small diodes or resistors located where the burn is, I guess the board just shorted there then?

[budm]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

Service manual:


I just got PS-10 today.

[Beretta6888]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

Anyone find a good capacitor to buy online, I can't find a cap with the right specs from the previous link to parts express.

[budm]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

http://www.parts-express.com/pe/show...umber=020-1429

This one does not fit?
there are two caps, one is 4.7 and another one is 6.8

[hardwareguy]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

If the chip cap burns on the solder side of the board, CHECK THE AUX SUPPLIES!

In many cases, the output MOSFETs will survive this insult. Use film caps in place of the bipolar electrolytic caps. (they fit with a little creativity).

[RonAlam]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

what type is the chip capacitor? I have the same sub with bad cap and burned out chip capacitor. Any help would be appriciated

[RonAlam]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

almost forgot, which side is positive and which is negative on the board? I have no way of telling.

[MtPockets]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

Working on mine at the moment PS10.

Are these Caps considered leaking or would this be adhesive to secure them? This way if it is adhesive i'll leave it be and check with esr.

That TH1 thermistor seems to have become a lil extra warm..
can someone direct me to a part # for replacement and new pad , As I've tried to cross ref the part number on digi key andd mouser but couldnt locate.

TIA

[999999999]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

Working on mine at the moment PS10.

Are these Caps considered leaking or would this be adhesive to secure them? This way if it is adhesive i'll leave it be and check with esr.

That TH1 thermistor seems to have become a lil extra warm..
can someone direct me to a part # for replacement and new pad , As I've tried to cross ref the part number on digi key andd mouser but couldnt locate.

TIA

Wow the factory did a terrible job of cleaning that PCB, though I've also seen a lot worse.

The substance under the capacitors is just an adhesive to keep them from vibrating around and wearing the seal and leads. They look fine, though if you ever were to replace them it might be good to apply some adhesive yourself.

It appears that it wasn't the thermistor that got hot per se, rather the heatsink and the potting material or whatever it was degraded due to being a bad formulation or something. I wouldn't worry about that too much, would just lather some fresh heatsink grease on the thermistor and put the clamp back on unless it completely crumbles away when trying to attach it. If that happens you could just bend the metal portion of the mounting clip a bit so it holds the thermistor against the heatsink without the black material and put a bigger glob of heatsink grease on it, or maybe a dab of silicone caulking between the clip and thermistor.

What is unclear is whether yours has any symptoms of malfunction, or is this just an inspection type servicing?

[ben7]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

In your third picture, it looks like that capacitor on the bottom right is slightly bulging.

Yes, those big capacitors are held down with some extra glue.

That thermistor, it's hard to say what happened.
I don't see any smoke marks around it, so I guess it was the same thing 999999999 said.

BUT, the crumbly stuff around it could be conductive .. some glues do that when they get old!

[MtPockets]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

The problem I was having was intermitent power issues going in and out of the standby mode.

[budm]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

The board uses bad brown glue, you need to remove them since they become conductive and also corrosive. The thermistor is part of the output stage bias circuit to protect it from thermal runaway, you can mount it back in place but you have to make sure it make contact with the heatsink since it is for sensing the temperature of the heat sink which the output transistors are mounted on, I use heat sink compound on it. When the temperature goes up, the resistance goes down to reduce the bias current through the output transistors.

[999999999]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

The problem I was having was intermitent power issues going in and out of the standby mode.

That is often a sign of a bad (or cracked) solder joint, that the change in heat causes expansion and contraction that can break the circuit. Also examine the entire PCB for hairline cracks that could break a trace.

[MtPockets]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

I've been searching and searching for bad joints under magnification and cant seem to pinpoint as of yet.. I do have a lifted trace on the bottom of the board where that Thermistor goes, Last picture I posted. Center of the picture next to D26

[999999999]

Re: Infinity PS-12 Powered Subwoofer Fired Amplifier

^ That is a bit odd, compare the part # to the specifications and resistance measurement, as well as a continuity measurement between the solder joint and the next the trace connects to confirm the trace is intact.

If it is, I'd glue it down then put a bead of epoxy over it right up until the solder joint. If not, put in a jumper wire between the two joints.

However, I don't see how that would particularly effect standby mode, rather what budm mentioned.