JBL Subwoofer SUB200/230 - intermittently goes quiet

[synapse]

Hi,
I have been given this Sub to try and fix.
It seems to go quiet after a while, sometimes turning the sub level dial at the rear makes it loud again. (when it's quiet it just sounds like someone has turned the volume down.

I thought this variable resistor might be faulty, but after removing it it seems to test fine, a nice gradual rise and fall in resistance on the multimeter.

Has anyone got ideas of what to check next?

[synapse]

Re: JBL Subwoofer SUB200/230 - intermittently goes quiet

These are top and bottom of the two boards inside

[synapse]

Re: JBL Subwoofer SUB200/230 - intermittently goes quiet

and this is a little add of board near where i removed the Potentiometer

[Khron]

Re: JBL Subwoofer SUB200/230 - intermittently goes quiet

On one hand, i don't suppose you'd be inclined to attempt to trace out at least some of the (input) circuitry, would you?

And on the other hand, on a Jamo Sub 200 that i bought faulty last year, both the low-pass adjust pot and the volume pot had went wonky, so... Even if the volume pot seems to measure ok, a replacement one can't be more than a buck or two It's not like they used Alps Blue Velvet ones as stock, anyway

[Agent24]

Re: JBL Subwoofer SUB200/230 - intermittently goes quiet

Could have been bad solder joints on the potentiometer - the movement caused by turning it may have restored connection momentarily.

Replace the potentiometer and if it still shows the fault, you could trace the signal with another amp or scope and see if you can find out what happens to it when it level drops.

[budm]

Re: JBL Subwoofer SUB200/230 - intermittently goes quiet

This may help.

[synapse]

Re: JBL Subwoofer SUB200/230 - intermittently goes quiet

Thanks guys, If i get a chance over the next few days I'll re solder in a new one then see what happens.
That service manual is gold, thankyou very much.

[synapse]

Re: JBL Subwoofer SUB200/230 - intermittently goes quiet

Just an update: Replaced the potentiometer and it's working like new now.

Thanks for your help.

[budm]

Re: JBL Subwoofer SUB200/230 - intermittently goes quiet

Thanks for the follow-up.

[Agent24]

Re: JBL Subwoofer SUB200/230 - intermittently goes quiet

Awesome! Good to hear.