Yamaha HS -80m Powered Speaker

[jackstratblues]

Hi,

I'm new hear so sorry if I've not supplied things correctly.....

I have a Yamaha HS 80M powered speaker that is mis behaving. I replaced 2 x 4700uf 50v caps in the power supply and all was ok for 24 hours. I've not done it yet but I think if I replace the caps again the same thing will happen so something else must be wrong. Now I'm back to the same problem - no audio from speaker - when you power off speaker the main speaker cone pops.

Any pointers?

Thanks in advance

 

[davenn]

hi there
welcome to the forums

umm first off ...

I would be very suspicious of the bridge rectifier (may be 4 separate rectifier diodes)
if they have popped then the capacitors are going to be getting some pretty harsh AC
and that could well be killing them

check what voltage the PSU is producing ... is its voltage printed on the circuit board ?

Dave

 

[KrisBlueNZ]

Google Yamaha HS80M service manual. You can download the service manual with a full schematic diagram. It looks like it's biamped with two LM3886 amplifiers, one for each driver, running from unregulated supplies of about +/- 30V (the actual voltage isn't indicated anywhere!) with regulated +/- 15V for the input circuitry.

Do either of the drivers work?

The data sheet for the LM3886 is readily available through Digikey etc. It describes the various safety features of the device and shows the pinout, so you can measure the supply voltages and other voltages on it. A reasonable place to start would be the woofer amp - measure the terminal voltages on the LM3886 and post them here. Don't measure on the actual IC pin wires; your probe might slip and short things out! Best to measure on the underside of the PCB with downward pressure.

 

[CDRIVE]

Were you sure to observe polarity when you replaced the caps?

Chris