2007-09-04
Limited Label DVDS500 DVD player This is a cheap DVD player which
is capable of playing DIVX avi files. It also has 2 microphone
inputs for karaoke function. Even if it is very cheap, it has
good features and above all a very good picture quality.
As
the image shows it is a very clean design with one power supply
pcb, the drive unit, three small boards for the front panel and
a motherboard based on the ES8380 video processor with
circuits for driving the motors, handling the display, front
panel keys and IR remote. The three boards in the front panel
are for the display and IR receiver, three front panel buttons
and the microphone inputs.
Layed
out on the table it doesn't look like much. OK, this is without
the powersupply and microphone inputs PCBs, but anyway.
The
unit was stone dead so I first suspected the power supply.
Thanks to the printing on the PCB that showed the voltage levels
this could quickly be ruled out since all voltages seemed to be
fine.
Next thing to check was the mother board. After some searching
on the internet it was clear that there wasn't any public
material available for the main circuits that was used. This
complicated things a lot. One area on the board had some through
hole components - a resistor, diodes and transistors, which was
rated for a little higher power. I suspected that this was for
driving the motors on the drive unit. After some more
investigations and circuit board tracing it turned out that the
higher power circuits wasn't for motor drive but was instead
used as an output stage for two linear power supplies. One for
3.3V and one for 1.5V, both powering the main IC. The 1.5V
output stage got very hot and had a very low output voltage. I
tried to apply an external voltage, at that time I didn't know
the exact voltage level, and at around 1.5V everything started
to work. I replaced the power resistor, since it measured a
value slightly different than its marking stated, and the drive
transistor. Naturally I didn't have that exact type but I at
least found a datasheet for it. I replaced it with one that had
higher power rating and about the same hfe. It still got very
hot but now the DVD player at least seemed to work as it should.
I didn't like the heat dissipation, which was probably what
killed the original transistor, so I fastened it to the bottom
metallic chassis that then acted as a heat sink. The tab wasn't
ground so it had to be insulated from the chassis.
This
seems to have worked. Time will tell if this is a permanent
solution. It could also be that there is something else that is
broken on the board or in an IC which caused the higher current
consumption, which in turn caused more heat in the drive
transistor and finally killed it.
2007-09-04
Limited Label DVDS500 DVD player
Layed
out on the table it doesn't look like much. OK, this is without
the powersupply and microphone inputs PCBs, but anyway.