JBL EON 515-XT repair

[xtian]

JBL EON 515-XT on bench, fails to power up--relay shuts off power after 0.5 seconds of operation, and thermistor is observed to get very hot during this short period, then unit draws only 10 watts thereafter. Found several references to this issue online, which led to the schematic and service bulletin, and this helped me identify two shorted MOSFETs, Q370 and Q371. I will replace these.

I'm hoping someone could help me spec parts at newark.com. I don't know whether to choose positive or negative Continuous Drain Current (Id) for the N and P MOSFETs.




Example, here's a likely N channel I found: IRFZ30PBF - VISHAY SILICONIX - MOSFET Transistor, N Channel, 30 A, 50 V, 50 mohm, 10 V, 4 V | Newark element14

[Jazz P Bass]

FQP17P06 - FAIRCHILD SEMICONDUCTOR - MOSFET Transistor, P Channel, -17 A, -60 V, 120 mohm, -10 V, -4 V | Newark element14

FQP30N06 - FAIRCHILD SEMICONDUCTOR - MOSFET Transistor, N Channel, 30 A, 60 V, 0.031 ohm, 10 V, 4 V | Newark element14

[xtian]

Many thanks.

[xtian]

I notice for the N channel mosfet, you chose a 50V part, instead of the 60v recommended in the parts list. Is this no big deal because we're dealing with 15v rails?

[The Dude]

He gave you the original part links reading from the schematic. Unless I'm missing something, it says 60V right in the description?

[xtian]

Oh, rats. I got the N Channel one mixed up with one that was already in my cart, and ended up ordering this:

VISHAY SILICONIX IRFZ30PBF MOSFET Transistor, N Channel, 30 A, 50 V, 50 mohm, 10 V, 4 V
There has been an error processing your request | Newark element14

Should work, no?

[xtian]

I got this unit working back in January, and it has continued working. But now its mate is in the shop. The HF channel works fine, but the LF channel does not. Speakers are OK. Since I have two units, I was able to confirm the preamp board is OK. The issue is in the power amp board.

Good schematics available. Please see attached Power amp schematic. 100Hz signal passes and looks good at TP350, which is on page 4, coordinates B2. But at speaker output, signal is low, and corrupted with lower and higher frequencies. Not sure where to test in-between these two points, and am confused about signal path on page 5.

Suggestions on how to further subdivide and conquer?

[xtian]

100Hz signal passes and looks good at TP350, which is on page 4, coordinates B2. This is the blue trace on my scope. But immediately after R331, at pin 2 of U305, the signal looks like crap. This is the yellow trace.

Voltage is present on U305 and U306, though a little unbalanced: 5.02v and -4.75v. But that shouldn't mess up the waveform that badly, right?

What's going wrong?

[mhuss]

The LF amp is a bridge configuration, which means both sides of the woofer are driven at the same time, with an out of phase signal. The op amp under TP350 inverts the signal to provide the out-of-phase drive signal. You should have a normal signal along the top branch (U305 to LF_DRV_L etc.) and an identical but inverted signal along the bottom (U306 to LF_DRV_R) branch.

[xtian]

Yes, I see an inverted, good signal after U303-C.

[mhuss]

How about at the collector of the two pre-drivers (Q301/302)?

[xtian]

Whelp, owner pulled the plug on the repair, and we're just going to replace the board with a new one from fullcompass.

Thanks anyway!

[lowell]

I have 2 of these in right now. The one I've looked at has a shorted Q371 power mosfet. Seems to be a trend.

[lowell]

Got another one in. Shorted FETs. Just wanna note I was stumped after replacing them and having the thing cycling. Make sure to have all those screws IN when testing it or it won't go! Added the screws and boom, fixed.

[xtian]

The screws holding the FETs to the heat sink?