Memory backup for Sony XDR-F1HD
by Hillel Hachlili
After a year of pleasant
experience with HD radio in my car (I have installed the Dual XHD6425), I
decided to upgrade my home office to HD radio. I found a good deal at Amazon:
$73 for the Sony XDR-F1HD. It performs very nicely yet I think that the Dual
car radio has more treble.
One problem is the heat
inside the unit. I think that the 3.3 voltage regulator IC901 which is mounted
on a vertical piece of aluminum generates a lot of heat that is transferred
through the PCB to the other 2 modules. The Transformer is also running very
hot. I have raised the tuner on a small stand to improve the intake opening and
put a small fan on the top.
The second problem is lack of
memory backup for the 40 presets. I have had a couple of unused Nokia cell
phone batteries BLD-3 lying around and I put one in through a 220 ohms 0.5 watt
resistor.
The battery backup also keep the clock running when unplugged from the
outlet.
I have measured the standby
current to be
By using a couple of testing
clips, I didn’t have to solder anything on the tuner.
The plus wire (red) is hooked
up to D912 cathode and the minus (black) to JW20.
If you try to follow my
solution, please be very careful to connect the clips to the correct points.
The unit could be damaged if the battery is connected to an incorrect point.
The Lithium Ion battery is a
good choice because it’s fully charged voltage is 4.25 and the voltage at D912
cathode is about 4 volts, so it can never get overcharged.
When the battery is empty
(2.4 V) it will be charged at 7.3 ma through the 220 ohms resistor. This
current will get smaller as the battery voltage goes up. When the battery
reached 4 volt the charging current will be 0. To fully charge a 700 mah
battery at 7 ma it could take 100 hours, but since the
current get smaller it will actually take longer than that. Since the CPU
backup current is about 10 micro amp., One hour of 7ma
charge provide 700 hours of backup.
I have measured the CPU
supply voltage at D914 cathode:
When the tuner
was on 3.25 V, when it was off 3.33 V and when the Tuner was unplugged (with a battery
charged to 4 Vdc) 3.64 V. These readings
are well within the 2.7 – 5.5V CPU specifications.
The BLD-3 battery has an
internal protection circuit that disconnects the battery at above 4.3 V or
below 2.4 V, protecting it from overcharging or over discharging. The circuit also protect the battery from a short or reverse
polarity, and draw about 5 micro amp. The
BLD-3 is also very cheap, as low as $1 at eBay.
This protection circuit will
protect the battery in my backup circuit if it wired in reverse: The battery
will discharge at 36 ma through the 220 ohms (dropping 0.288 watt across the
resistor) until the protection circuit will disconnect it.
Since the CPU supply is rated
as 2.7 – 5.5 vdc, I don’t think any damaged could be caused by connecting the
red (plus) clip on the wrong side of the D912 or D914, but for the correct
backup current and CPU voltage it should be connected to D912 cathode, as shown
in the picture.
For more in depth review,
please read Brian Beezley’s report:
http://www.ham-radio.com/k6sti/xdr-f1hd.htm
and Julian Hardstone’s report:
http://www.rosestone.me.uk/XDR.html
If you have any questions, you
can email me at:
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