BY ROBERT ARMSTRONG
■ FIGURE1. MP3 BOARD 13 and 38 are both connected to
VCC and these two pins are
adjacent. Don’t panic when they show up as shorted! Likewise, pins
14, 39, and 15 are adjacent and are all grounded. There should be no
other instances of adjacent pins that are connected together.
Once you get this far, take a break. The hard part is done, and the rest
is an easy job of soldering a bunch of thru hole parts. Use care when
installing the headers for J3 and J5 (the VFD and LCD connectors) —
pin 1 of each connector is on opposite ends; this was done to improve
the PCB layout.
Note that JP1 is just a single pin; it’s installed next to JP2 and
shares one of its pins. Be sure to solder the top of the CPU crystal
to its ground plane for mechanical stability and so it’s electrically
bonded to ground.
Finally, remember that the VR2 will require a heatsink if it’s used
to power an external vacuum fluorescent display.
Testing & Programming
■ FIGURE 2. JUMPERS SET
locked into place.
The pads on the CF socket are 25 mils
(0.025 inches) wide and have 25 mils
between them. These pads are very thin
and will separate easily from the PC board
if too much heat is used. To solder the pins, you’ll need a temperature-controlled soldering iron with an ultra fine 0.015-inch diameter tip,
some 0.010-inch silver solder, and some extra fine solder wick to fix
the inevitable solder bridge.
With a little practice, it’s not that difficult — just touch the tip of
the iron to the pad on the PC board. Count to three while it heats up,
and then touch the solder to the end of the CF socket pin. Try to avoid
touching the iron tip with the solder if you can. If you do it right, the
solder will only melt on the one pad/pin that’s hot, and it’ll wick up
between the pin and the pad.
If you use too much solder and short to an adjacent pin (and you
will at least once before you’re done with all 50 pins — take my word
for it!), use your extra-fine solder wick to remove the excess.
After you’ve gone to all the trouble of soldering on the CompactFlash socket, you really should invest 15 or 20 minutes in testing it
before you proceed. The CompactFlash socket is extremely difficult to
work on after the other parts have been mounted, and if there are any
shorts or opens, you want to find out now, not later.
To check for opens, use a small sharp tool, such as a dental pick,
to gently push on each and every pin. If the pin moves, then you
need to fix it; a pin that’s firmly soldered in place won’t budge when
you poke it.
Checking for shorts requires that you use an ohmmeter or
continuity tester to check every pair of
adjacent pins for a short. Notice that pins
You’ll need to make up a power cable to connect to J1 (remember that
the center pin is positive) and a standard audio mini-plug cable for J2.
There is no amplifier in the MP3 player, so you’ll need to connect J2 to
a set of powered speakers or an external amplifier.
You’ll need a 14 conductor cable with 0.1-inch IDC headers to
connect J3 to your LCD display, or a 16-pin cable to connect J5 to your
vacuum fluorescent display. Remember that the VFD display pinouts
aren’t always standard; be sure to double-check yours against the MP3
player schematic. If your VFD does have a different pinout, just make
up a custom cable for it.
You’ll need a six conductor cable to connect the rotary encoder,
which is usually mounted on the front panel along with the display.
And lastly, make up a cable to connect J7 to the serial port on your PC
(either a DB9 or a DB25 connector). The serial port connection uses
only three wires — RxD, TxD, and ground — be sure to remember to
connect J7 pin 4 to pin 1 (ground) to enable programming mode.
Install the remaining two ICs (the DS275 and the P89C664) in their
sockets, and set the jumpers for programming as shown in Figure 2.
Connect a voltmeter to the output
(C15 side) of VR1
and, if you’ve got
a spare meter, connect a milliammeter in series with
the power supply.
Do not install
card, connect an
LCD or VF display,
or connect the
■ FIGURE 3. FLASH MAGIC SCREEN
November 2005 NUTS & VOLTS 39