Hi everyone, I'm new to this community and recently found this thread on fixing the Bar 48.
I'm a speaker repair hobbyist and recently a customer brought to me his Bar 48, complaining of no power.
As SixerFixer has already written, the problem is related to the 5V output of the smps. Basically the smps could not sustain 5V when the sound processor chip is drawing current to power up the system, resulting in the voltage dipping to 2.7V. Thereafter the chip may sort of hangs itself and releases the drawing current, thereafter the voltage will rise back towards 5V.
I've pin point the failure to be caused by C05 and C06, both being 220uF 16V electrolytic capacitors. There may not be any visible damage.
For my case, 1 capacitor measured 169uF with ESR 0.4ohm, the other 30uF with ESR 4.5ohm. The latter part is closest to D02 (rectifying diode for this circuit).
My initial fix was to replace the 2 capacitors with similar size and specifications type. The speaker did work properly however both capacitors were running very hot and it's only a matter of time before they will fail again. Without going much into technical discussion, basically the board requires very low ESR type capacitors to sustain a longer life span.
My final fix is to replace C05 with 2x 100uF 50V (United Chemi-con KY series) capacitors soldered in parallel. This capacitor measures with ESR of about 0.17ohm. By connecting them in parallel, I effectively half the ESR but double the capacitance to 200uF (short of 20uF but still good enough). You may try purchasing a low ESR type capacitor of the same 220uF 16V, but I find it nearly impossible to have the right size that fits.
I've also taken the opportunity to remove some of the silicon rubber glue surrounding D02 in order to give better cooling to that area.
The extra capacitor is inserted onto C44A. The leads needed to be bent slightly to fit in the space. I've also deliberately mounted it in 'reverse polarity' with the aim of using the copper traces beneath for bridging.
Below shows how the soldering was done. The yellow 'L' is kapton tape, to ensure no accidental bridging between those traces.
The end result is that all the capacitors running cool to touch. I'll presume with cooler temperatures, this smps should last much longer than intended.
Hope this info is useful for anyone out there.
Cheers!