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 micro amp. With the 700 mah battery, the backup could last about 5.3 years !!!.
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:
and Julian Hardstone’s report:
If you have any questions, you can email me at: