JBL EON 518S Power Supply need help

[Zaldoran]

Hey you guys,
I'm getting stuck to fix a switchmode power supply of that sub. A colleague has a plenty bunch of these subs, which regulary come in with blown smps (probably due to lousy generator supply), with both mosfets and the 47R resistors blown. No big deal so far.

But the latest unit makes me a headache. It came with a bigger mess (input filter caps, mosfets, bunch of resistors, E13003 and MPSA44 transistors, switching controller and unknown z-diode blown - so hardly everything in the primary section was gone. I've replaced all the components (identified the z-diode marked H1 as an 11V/500mW MMSZ5241BT1G) and everything looks quite nice. However, the SMPS operates for about one second drawing an extraordinary high current, and keeps blowing the mosfets. The bad point is, I've no clue why. I've doublechecked everything with CT, and it looks quite well. My best guess would be a winding short in the transformer (apparently to the filter caps, this unit got more than 230 Volts so probably insulation crack due to overheating). Do you have any experiences, probably schematics of the power supply?

Best regards
Holger

[The Dude]

Just responding to subscribe to the thread. I'm battling one of these with the exact same problem at this very moment. I'll update if I figure anything out. Haven't been able to locate a schematic either. I called JBL and was told they don't offer schematics or parts and that they simply replace modules.

[Jazz P Bass]

JBL PRX 518S Schematics

Not too sure if this is the one but I gave up & bought a new power supply.
Crown Audio is who I contacted.

[The Dude]

I have that set Jazz. Mine is a different animal altogether. Maybe it will help the OP, though. At any rate, your efforts are much appreciated!

[Jazz P Bass]

I would try contacting Crown Aucio.

They may have a schematic that is more appropriate.

[The Dude]

The company I work for is a Harman dealer- Crown, JBL, etc. I contacted them already and was told no schematics or parts. The only thing they offered was new modules. I may end up going that way if this thing gives me any more trouble.

[km6xz]

Were Q5-Q8 damaged? If so the T2 gate drive transformer might have a cracked core rather than a short which would prevent Q1 and Q2 from even trying to switch Vbulk. The 47 ohm resistors you said were taken out, were those the gate series resistors? That would point to damage to T2. The more common failure for transformers is the T1 with a cracked core. You could test if for shorts but a turns ratio measurement, by injecting a high frequency signal, 500khz or higher into terminal 7 and 10 and see what voltage ratio you get across terminal 11 and 14 with the transformer out of the circuit. It would be 3:1 or 4:1 or in that range. If it is much lower than that the primary is shorted. Make sure you do not have a secondary short at the output of T2, a shorted bridge BR1 or caps C4/5 could appear to be a shorted transformer T2.
JBL treats these supplies as a unit replacement and does not even want shops repairing them because more SMPS supply repairs turn out badly than other circuits. They are cheaper to replace for them than repairing them.

[Zaldoran]

Not too sure if this is the one

Thank you Jazz, but these aren't. I've found a set of schematics iirc at ElectroTanya but the SMPS is not included.

[Zaldoran]

Were Q5-Q8 damaged? [...]were those the gate series resistors? [...]

Yes, these are the gate resistors. However Q5-Q8 were some of the few parts which survived that mess. Meanwhile I pulled out a working SMPS and interchanged T1 and T2 with the bad one, turning out that these aren't the problem either. Also no short at the secondary side....

[Zaldoran]

Okay, got it for this unit. It was nothing but a bad via on C8. Probably I've damaged it while desoldering of the blewn cap. Put a wire across C8 minus and BR1 minus and its working fine again.

[km6xz]

If you work on these I have the service data but it is 24mb so I can't up load it here. Congratulations on getting a tricky one.

[Zaldoran]

I would appreciate that. I'll send you a pn.

To be honest, that spot belongs to my employee who said "If every component is fine, the fault must be the pcb". Well, sometimes you'll miss the forest for the trees

[km6xz]

PM replied

[giromusic]

Hello km6xz, I also have a big trouble trying to repair that smps.... and I can't find the schematic or service manual...
Is it possible for you to send it to me? you can email me to giromusic@hotmail.com
Thank you very much.