bose ps48 bass module psu defect

Hi,
i have this bose psu,
and i finnaly got i repaired when replacing several diodes , mosfets and ic.
U101 = L6598D
R101 = 10 ohm
R102 = 33 ohm
Q101 = STP9NB50F
Q102 = STP9NB50F
D101 = K6 (MMBD914L1)
D102 = K6 (MMBD914L1)
and optocouplers.

Amp works but only renerates about 12 volts.
when music goes over halv volume, the voltage drops alittle. and bass start distorting.

I read that the psu should varitats via a lowpass filter and have a voltage between 12 and up to 24 volts.

but obviously this is the problem .

Any one have any experience with this module ?

best regards
NIklas.

Any time you work on a PSU, check the capacitors, especially the ones in the power circuit - the input and output smoothing caps.
They often loose capacitance with time and/or go high resistance.

I will check, but psu works at normal level 12volt.

trean27 said:

I will check, but psu works at normal level 12volt.

Click to expand...

Do you have an ESR meter?, the almost universal failure mode of electrolytics is high ESR, it's pretty rare for them to be low capacitance.

High ESR capacitors would also explain why the PSU died in the first place, and as Bose is usually cheaply made in China it's likely to have sub-standard capacitors.

I presume you don't have a schematic?.