Hello,

Where can I find the schematic diagram or service manual for the JBL LSR 308?
I can't seem to find it.

The speaker suddenly started crackling out of nowhere, even without any connected input.
Please see the video at the bottom for a sample of the sound.

I took it to an electronics repair technician yesterday, and he mentioned that the power amplifier is functioning properly, but the preamplifier section is not working well.

However, he's unable to find the schematic diagram or the service manual for the JBL LSR 308.

He mentioned that he needs these resources to diagnose the issue.

Any assistance in finding the schematic diagram or service manual would be greatly appreciated.

Video of the speaker issue:

Thanks for your anwser,
VMP

 

Welcome the group without any circuit information.
And an on-line search will provide 1000 hits for ebay wanting to sell you the same half dozen items. That has been my experience in doing a general search.

Without a circuit the diagnostic routine would be to disconnect the signal inputs to rule out an external problem. Then vary the volume control to see if that affects the loudness of the noise. Then thump on the case, because a loose connection or a dirty switch can cause the creackling sound. So far no tools except hands and ears required. If the noise does appear to come from a control , then an application of control cleaner can fix it for a while.
But if none of those have any effect then the problem may be electrical.

 

Thank you for you reply.
- No input is connected.
- When the volume is set higher the noise get louder, it's not the potentiometer.

 

Thank you for you reply.
- No input is connected.
- When the volume is set higher the noise get louder, it's not the potentiometer.

Since the volume control changes the noise level, we know that the noise source is in a stage before the control. So it is not the output transistors or the driver transistors.
To continue the mechanical checking now, gently tapping the individual components in the section before the volume control may reveal the noisy part. This will need to be done with speakers conected, the amplifier on, and the volume control turned up. It may not reveal the part, but the probability that it will is great enough to make it worth the effort.