Gareth Magennis wrote in message
...
"David Farber" wrote in message
...
This Bose CD-3000 tabletop player was brought to my attention because
intermittently there were popping/static noise was coming out of the
speakers. It was quite loud. When I powered it up via the 12 volts
input,
the problem didn't seem so noticeable. I took it to the shop, opened it
up, and noticed there were two car stereo-type speaker amplifier chips
powering the speakers. Using these two datasheets,
http://www.datasheetcatalog.org/data...onics/1512.pdf and
http://pdf1.alldatasheet.com/datashe...LECTRONICS/TDA
7375.html I
was able to figure out that the TDA7375 powers the left and right
speaker
and the TDA7396 powers the subwoofer. I checked the prices of replacing
these parts and each one was less than $10. Since the pc board where
they
resided was difficult to access and make tests while powered on, I
decided
to replace the stereo amp chip. It didn't help. I figured then it had to
be the other chip. I replaced the other chip with no improvement. Then I
figured out a way to remove all the pc boards and cables and power it up
outside the unit where I could make some meaningful tests. First of all,
there was some small dc offset going to the subwoofer. I soldered a 330
ohm 0.5 watt resistor across the subwoofer output terminal so it would
have some load. It was about 340mv. Not great but certainly passable.
Then
after about 15 seconds, the dc shot up to 12 volts and my bench meter
showed a spike in current. This voltage swing delay occurs every time I
power it on. If I just disconnect the subwoofer, the left and right
speaker outputs are fine. A schematic would be of immense help here or
perhaps someone has had some experience with this unit. Any and all
suggestions are welcome.
Thanks for your reply.
--
David Farber
Los Osos, CA
Could this be yet another "conductive glue" problem?
(See the "TDA7295" thread here, first post 18/3/13, last post confirming
this problem 29/03/13)
Gareth.
Either that or a failing minor supply to an op-amp farther back, eg a small
cap on one rail, is my guess. Either way requires tracing back from the
input/s to the output device