jbl es150p subwoofer current transient....?

[ilyaa]

this one was blowing fuses -

i was getting a short across V+/V- - traced it to the MOSFETS on the little breakaway power amp PCB. fortunately or not, the FETs are the pretty much the only non-SMD/miniature parts on that board - so it was possible (although hard) to replace them. i did. amp worked! phew. put it back together - BAM - another fuse blown.

checked the FETs, two of them - q10B and q11 - had blown, but not q10.

took the power amp board out, turned the amp on with a limiter in series - all good. at this point i figured it must be something else on the power amp board - SMD bullshit - so maybe time to give up.

BUT, there is one weird sympton that id like your guys' help with: even with the bad FETs out of there/the power amp PCB unplugged, when i turn the amp on, my limiter will sometimes glow really bright (like full on short bright) for a split second when i turn it on. it blew a 3A slow blow fuse (with the power amp/shorted FETs out of circuit) once, even. it does not do this every time. sometimes i turn it on and i get a normal dull bulb for a second that gets even duller after the initial switching on. but, like i said, SOMETIMES the bulb will light like there's a short but just for a second.

what's going on here? something is causing the current to spike but only sometimes and just for a second.........any thoughts?? bad rectifiers? bad filter caps? so hard to tell because otherwise it works! voltages/ripples,etc look fine!!

hmmmm

[J M Fahey]

Bright blinking is normal and expected, you must first charge those big empty supply filter caps.
The point is what happens after those first 2 or 3 seconds (at most).

[ilyaa]

hmmm

but is there a possibility that initial charge is problematic?

like i said - this amp was working fine and then just blew a fuse instantly upon turning on again.

shorted power amp was the likely culprit - BUT i removed the power amp and it blew a fuse then, too...but when i plugged it into a limiter after that: no short!

[J M Fahey]

hmmm

but is there a possibility that initial charge is problematic?

No.

like i said - this amp was working fine and then just blew a fuse instantly upon turning on again.

Likie Enzo says, everything works fine until it fails.

shorted power amp was the likely culprit - BUT i removed the power amp and it blew a fuse then, too...but when i plugged it into a limiter after that: no short!

What do you mean by no short?
Does the amp work fine, have sweet sound, whatever, when plugged into a series lamp?

Or you men the fuse didn´t blow?

because if you think the latter, that´s exactly what the limiter lamp is there for, does not mean the amp now is healthy.

[ilyaa]

lemme try and explain it again.

this is what's strange:

after removing the power amp PCB - i turned the amp on with a bulb in series: no short.

i took the bulb OUT of series and just turned it on with the recommended 3 amp fuse: fuse blew.

i turned the amp back on with a bulb in series IMMEDIATELY after: no short.

i wouldnt be puzzled if it wasnt puzzling......

that's why i thought there might be a possibility of a current transient that was blowing the fuse or the FETs - but im not sure what could cause that or where itd come from

[Enzo]

turn-on transients the bulb prevents but the circuit on mains does not.

[ilyaa]

enzo,

do you mean that there may well be a turn-on transient issue?