JBL PB12 subwoofer, Class D amp, dead.

[JohnW]

Hi Pat (& Chris),

I'm sorry its not the same module as I have - could still send you one - if you want to try and shoe-horn one onto the plate - seem to recall they operate on single HBridge rail and -/+ 15 or similar for Opamp / modulator. However not sure if its worth it, as the modules I have are very poor performing - might be able to dig up measurements - if I can find them..

John

[ssanmor]

If you want the schematics of the JBL PB12, please e-mail me.

Best regards

[pat allen]

Ok, so here i am, i have opened the sealed module with the help of a milling. I have access to the power mosfets, wich are totaly ok.
ssanmor sent me the schematic of it all, the the inards of the module dont match with the schematic.

I think i will manage to build a new module myself, pcb,...

[classd4sure]

Hi,

Nice work slicing that open.

If not the mosfets, can you tell us what is cooked on it? I read it is due to a flaw in the circuit, so I trust you plan on changing a few things.. where did they screw up with it?

Thanks

[pat allen]

I dont know yet, i havent removed all the epoxy, wich is difficult to not damage physicaly the components, i will surely fond what happened, and fix or improve it.

[classd4sure]

Neat, good luck, please keep us posted

[pat allen]

So, i have mastered how to remove that stuff, man that stink !!
With a light flame torch, just heat it up without scraping it with a screwdriver too soon as i did, and it removes like a champ.

I went a litle bit too strong, but if i have another module i will be able to open it without messing it all like i did.
Anyway, i will do a full reverse on it.
the 2 chips are schmitt triggers, MC74ACT14AN, the small one is a LF358. There is also a small transistor, mpsa42.
All the others components are regular resistors, diodes and caps.
There is no SMT parts on this board. There is no reason why they did encapsule this part in epoxy. Is there a patent on this?

anyway, if i could only find the real schematic of it, i will figure what went wrong. Looks to me like one of the schmitt trigger have failed, since the power mosfets are ok.

any toughts?

[pat allen]

The under of the module, where i discovered to my absolute dismay that there was no components.

[JohnW]

Hi Pat,

37 Minutes left of this year!

Are you sure one of the 14 Pin DIL is not a MOSFET Driver?

John

[pat allen]

ha! i am in CANADA so it is 5:24pm here, sorry

No, they are realy schmitt triggers, i was able to read very clearly all the parts numbers.

The schematic that i have shows effectively some sort of driver, wich is a IR2111
IR2111 data sheet
I guess the module i have is the "old style" where they managed to drive the mosfet with the schmitt triggers, and the "better module" have the IR2111. It does not match at all with the schematic anyway.

pop me a message when you will celebrate !!!