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07-08/2013 —
TELE-audiovision International —
全球发行量最大的数字电视杂志
1. The Nokia DLR-2L cable features a TTL
to RS232 converter and can be used to
connect the COM-Port of a PC with a TTL
interface. If your computer does not have
a COM-port anymore, you can just use a
RS232 to USB converter. Bear in mind that
neither the Nokia-cable, nor the RS232 to
USB converter cross the TX and RX lines:
you will need to cross them yourself. Pay
special attention to just use TX, RX and
GND. The second pin on the AZBox PCB
is not to be used. Doing so can quickly
fry the circuit on the AZBox and then
you are definitely locked out of any TTL
restoration.
2. See the white dot on the PCB, close to
the 4 TTL pins? It marks the pin #1. On the
different AZBox receivers the pins have
always the same function:
Pin 1 – TX
Pin 2 – VCC
(Warning: do not use this pin!)
Pin 3 – GND
Pin 4 – RX
3. When everything else fails, JTAG is your
last resort before having to flash the chip
externally. But before being able to do so
it is convenient to solder some pins on the
JTAG port, because the manufacturer left
those out.
4. In order to prevent accidental writing
to the flash chip a jumper exists. If not
closed, the JTAG cannot write to the flash
chip. This means that a jumper needs to
be soldered. Because the two pins are
really small, I just soldered a small wire.
Later on, instead of de-soldering it, I cut
the wires open, obtaining two small and
fragile pins, which can be closed without
further soldering.
5. This is the most difficult part of the
JTAG retrofitting, as you do need proper
equipment. I used a hot air soldering
station to obtain two 103 resistors from
an old motherboard. Using the same hot
air station, I soldered these two miniscule
resistors to the AZBox PCB, close to the
JTAG port.
6. The parallel JTAG adapter used in this
process consists of soldering a total of
four 100 Ohm resistors to a male DB25
connector. These are soldered each to
pin 2, pin 3, pin 4 and pin 13. Finally,
pins 20 to 25 have to be shunted. From
each resistor and from the shunted pins,
connect wires, as short as possible, to the
pins of the JTAG port on the AZBox PCB.
Connect the wires like in diagram right.
7. Connect the wires according to this
drawing
8. If TTL recovery seemed like open heart
surgery, JTAG flashing is equivalent
to brain surgery. Extra care has to be
taken to avoid that any wire touches the
receiver on the wrong spot. To prevent that
the casing of the open DB25 connector
touches the receiver, I used a bit of paper.
Put something heavy on the parallel
port cable, to prevent the cable from
accidentally moving, which could make
the thin wires go off. The receiver has to
be turned on during the JTAG process,
so beware that there is live current on the
open receiver. However, AZBox receivers
normally use an external power supply,
so you should not get hurt, even if you
touch the receiver. This is not the case on
receivers with build-in power supply. In
these cases you have to be extra careful
and advise other people in the house to
not get near the receiver.
