On Aug 20, 11:58*am, "N_Cook" wrote:
Peter Kolbe wrote in message

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Good Day All

I have a Phonic SEM712A Powered speaker that I am in the process of
repairing.
It has 2 Power Amp Boards (Identical, One for LF, and One for HF). The
details on the amp boards are : 94v0 pan ks 14, SEM712A/715A AMP(H),
PCB Rev_1, 290-37D90-200-0.

The LF Board developed a fault, where it was crackling, and later
smoking.
When I opened up the unit, I found that
R312,R317,R318,R319,R320,R326,R327 Are all burned that you cannot
identify the bands. They all are 1/4w 5band resistors, which are on
the emitters and other of the Q304 and Q307 transistors.

When on the bench, the 2SA1943 Power transistor got so hot that it
actually melted its solder. After a short bit the SMPS was shorted and
ticking....

When I removed the 2SA1943 and powered up again (i think that was a
bad idea) The SMPS did start up fine, but then there was big sparking,
flames and crackling from those burned resistors.

The HF board is identical, so I swapped positions on the PSU/Preamp
board, and the LF worked fine. So It is definately only on the 1 amp
board.

I can get the values from the other board, to replace the resistors
and do comparisons, but perhaps somebody can help me out, as Phonic
does not want to give me a schematic.

Thanks
Peter

When powering up again , locate main rails and power good amp from say +/-20
current limited bench power supply and note a few voltages. Then try the
repaired board to see if much the same voltages. Perhaps list the R values
and place here if no info out there.

Maybe the PA part of one of the Phonic power pod mixer-amps schema on
eservice and elektrotanya is similar enough to be a guide. If there is
please report back here.
*Is Phonic rebadged as another name?

Thanks for that.
I do not think it is rebadges, as the Silkscreen on the board says
phonic.
When I can I will do the other suggestions.
BTW here are the pics of the faulty board, and the good board.

http://www.flickr.com/photos/kolbepeter

Thanks
Peter