On Fri, 15 Aug 2014, Mike Rivers wrote:
On 8/15/2014 11:29 AM, Jay Ts wrote:
A sharp, hi-res photo can show a lot.
At least a few of us here on RAP would find a photo of the PCB
interesting and informative.
It's gone now, so I can't take a photo for you, but for future
reference, what would you like to see?
In terms of the circuit and performance, if you can get the printing on
the main chips, such as the codec, it can help identify the exact part.
From there, it's possible to look up the corresponding datasheet and
learn a lot about the quality of the product.
It's nice to see the brands of electrolytic caps in the power supply
section, too. There are many brands of very cheap and unreliable Chinese
caps on the market, and a few that are well known to be top quality. It's
a very common point of failure, so it matters. (And it's also easy to
repair if those caps are through-hole.) You don't need to get that in the
photo; if the caps are Nichicon, United Chemi-con or Panasonic, just tell
people.
In general for SMD chips, there are footprints that are so tiny that
virtually no human can solder them, but there are also older, larger
footprints (such TSSOP) that are just half of the 0.1" through-hole
packages from the 1970s that we all love.
It requires learning a few
new tricks, but they are actually very easy to work with. I repaired my M-
Audio DMP3 with a TSSOP chip, and it was the first time I ever worked
with an SMD chip!
Incidentally, I tried to get a good picture of the different color
states of the meters and it just wouldn't work, even with a fully
adjustable digital camera in the hands of a decent technical
photographer friend. If the top red section was on, half the meter
photographed red, and that's not what it really looks like. My friend
speculated that a film camera might work better for this application,
but we didn't bother.
I have much better than decent technical skills in photograpy.
From what I'm seeing in the photos in the article, the first thing you
need to to is use brighter lighting so the light level on the case more
closely matches the brightness of the LED display. The LEDs are simply
overexposed, which will mess up the colors.
After that, you may need to adjust the color of your lighting to match
the color balance of the LEDs to the other things in the image.
To get your camera's color balance set right, use a standard photographic
gray card that has a flat spectral response and about 18% reflectance.
(E.g., Kodak R-27) Then use the camera's custom setting for color balance
(or "white balance") with that as the reference.
I think that much should do it for you, but I can't be sure. If not,
there are further refinements possible.
Maybe one out of a few hundred
users will have the tools and skill to repair it, that is, assuming you
could get a schematic and board layout drawings from the manufacturer.
It's not always necessary to have an exact schematic or understand the
circuit completely. Often, designs are based on reference designs they
got from the manufacturer. I repaired my DMP3 just from looking at the
circuit board and discerning how the circuit generally worked, looking at
the INA163 datasheet, probing some pins to see that something was wrong,
and making a logical guess. It was easy.
That doesn't happen all the time, but sometimes it can be like that, or
even simpler.
But in the real world, if anything on the circuit board goes, perhaps
with the exception of a power supply component, it's not going to be
repairable by anyone but the factory.
It really depends, and that is why it's nice to see a pic of the circuit
board. If there are no custom proprietary chips, and you can identify all
of the chips, and look them up on Mouser or Digi-Key and order in
quantity of one, that's a big plus!
I've replaced a couple of SMD 2-terminal parts if there's some working
room, but this was so cramped that I didn't have tools small enough to
work with. But then, I'm still in the analog and discrete world when it
comes to service.
Look up "soldering smd" on YouTube. There are some really good lessons.
(Try Dave Jones's EEVblog.com site - Episodes - #180, #183, #186,
#434.) I got over my fear of SMD that way, and now I think, "If they can
do it, I can."