JBL EON 518S Sub advice

[cablercdd1]

I've got a JBL EON 518S Sub that someone asked me to look at. The switching power supply appears to work well and the preamp signal led lights up when I apply a tone but that's as far as it gets. I haven't been able to score a schematic from JBL. At this point I'd like to isolate if the problem is in the preamp board or the power amp board so I can just order the appropriate board. Anyone have any experience with these?
Thanks
Paul

[Brad1]

May we assume that you have checked for continuity from the output board to the sub speaker, and checked continuity of the speaker itself (not open, or shorted)? Have you injected signal to the sub input, and checked for output signal at the sub speaker output to sub speaker? Have you connected speakers (or checked for signal) at the satellite outputs, with signal injected to the sub input? In other words...does the amp produce signal to the satellites, but not to the sub speaker? No signal passed to anything? Have you checked the functionality of any switches to make sure they aren't open?

I will ASSUME you already knew all that, and not trying to insinuate anything. Just making sure, since you haven't specified what you have actually tried. Just making sure you are sure it's in the board electronics, and not mechanical or a bad solder-joint, disconnect, open speaker winding, or open switch...before going through the trouble and expense of a new board.

Brad1

[Jazz P Bass]

JBL PRX518S Schematics

Here is what I have, as far as schematics.

Be aware that the output section is a Class D device.
Also, there is a standalone 'modulator' board (which drives the Class D outputs) that also has to be proven out.
(which must be ordered separately if you order the main board)

[cablercdd1]

Well first, I did a little signal tracing. The pre-amp has a balanced A and a B input and output and a speaker level input with a 1/4 " jack. I was able to get the signal through to the preamp output but I don't seem to get it to the Amp. Without a schematic I'm pretty much just guessing. Jazz, thanks for the PRX files but it doesn't resemble those. So while I was trying to signal trace in the preamp, the power supply spectacularly blew up on me. I was being real careful but I may have grounded something out with my scope. I'm going to order a couple of mosfets (IRFP460) and a burnt resistor and hope that's all that blew. I'll attach some pictures of the unit so you know what I have.

[diydidi]

Isolation transformer comes to mind. JBL units are PITA to work on. I like the EON's beter.

[cablercdd1]

Good idea. Guess what I have one and neglected to use it. My bad.

[km6xz]

Unless you are very familiar with switch mode power supplies and Class D digital power amps, you will be much better off replacing boards or better, sending it to someone who is a authorized JBL warranty station. The SMPS can be very dangerous if not fully understood and equipped with the proper test instruments. You and the customer will be much better served if you bail on it and send it to a specialist. You can repair 4 analog A/B amps in the same time consumed dealing with this unit, so you are going to lose both money and productivity by even working on it.

[paleeman]

Hi cablecdd1
You said that the amplifier has input signal indication, but no output. According to this the power supply kicks in, but possibly some secondary voltages are missing. For the amplifiers (two channels bridge mode) to be able to work, the 125 kHz signal is required to the U802 - TL494. Then he powers up the amps driver circuits via Q804. The first thing is to check the supply voltage to Q804, 15V at pin 12, and the 125 kHz PS at pin 5. If the secondary supply voltages +VCC and -VCC are present and the Q804 is delivering VGD, then you have a faulty amp section.