JBL LSR-305 failed amplifier

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asiadiy

Member
Joined 2019
#1
I was recently given a pair of these neat little speakers, LSR305 (original model). One has a failed amplifier board. Sadly, the replacement cost of the board is close to the cost of a new speaker.

Probably crazy, but I am thinking about modding them both to passive, adding DIY crossover networks and running them off a normal amplifier.

I would only want to do this if it actually might sound better than the original setup. Otherwise use as a mono PC speaker, and scrap the second.

:whazzat: Scrap or Mod? :whazzat:




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#5
asiadiy said:
I looked around for the schematic, but no luck so far. I messaged JBL Pro support, but not expecting them to give up their IP to just anybody.
Click to expand...

Unfortunately that is becoming more common with each passing day. The right to repair is almost gone because of it and piles of easily serviceable stuff are beginning to accumulate all over the world.

Last summer a friend and I went to a local dump and with the manager's permission we pulled a pickup truck full of old PCs and Laptops out of the piles. In the end, half of them worked when we plugged them in. Another large group simply needed OS reinstalls and only a small minority needed actual repair work. From that batch I think we only scrapped about 6 of over 100. Oddly, I think most of it was because of Windows 10 ... people were (stupidly) buying new computers to get the OS.

Anyway, back to your problem...
I don't know how good your trouble shooting skills might be, so forgive me if I'm either talking down or above you...

You have one working speaker, ya?

With a voltmeter and an oscilloscope you could most likely compare the two amplifiers to find out what is wrong with the dead one.

Start with obvious things like fuses, switches, power supplies etc. If all that is well, check for a DC offset on the speaker, this usually indicates a blown output stage. If all is still well, continue tracing the audio from the input and find out where it stops. From there direct comparisons between the two boards might reveal your problem.

If it's a "chip" amp (and being medium power class D it almost certainly is) get a copy of the chip's data sheet and make sure the operating conditions are right. Then, once again, if all is well... it probably is a matter of replacing the chip.


Can they be turned into passive speakers... Sure they can. It's just a matter of a small hand full of parts and some computer software, should you decide to go that way.

I hope that helps ... and good luck with this.
 
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#7
Thanks for the tips. Yes the world is moving towards trash and replace, sadly.



Unfortunately I do not have a high enough skillset with component level troubleshooting to do much more than basic probing around.



Good idea, I will power them up side by side and see if I can locate where things drop out. Everything appears fine, no bulging caps, fuse tests ok, nothing smoked, no cold solder joins.



The amp chip is STA350BW.



Another guy has been deep inside the speaker and posted some info.
JBL LSR305 no power, loud bang, defective repair. - Gearslutz
 
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