IC-7300 dead clock battery issue fixed

So the clock battery in my IC-7300 failed. Yes, the rig has been switched off for longer periods of time. Well bad luck. I compared the RT clock circuits of the IC-7300, IC-9700, IC-7610 and IC-705 using the service manuals that can be found on-line. Interestingly, the circuits in all rigs except the IC-705 are identical. Actually the clock circuit in the IC-705 is just a little different.

“I have a clock in my shack, don’t need one in my rig..” Well true, I also don’t need a logbook program, I like to write. I don’t need the dx cluster, I like to listen to all bands at the same time all the time. Don’t need PSK reporter, I ….

The recording feature in the IC-7300 is a wonderful thing and very well implemented. Perfect for recording that pileup, special event station, or to document a special QSO. But when all recordings are labelled with first of January and take place between 00:00 and 01:00 o’clock, this feature becomes useless. So the clock has to come back to life again.

I found two no-solder solutions: 1. leave the PSU on all the time and 2. set time/date with script from PC after turning on the rig. With solution 1. I’m burning up energy. My Alinco DM-340MW linear power supply consumes 25W when idle. This is (25*24*365/1000)  219 kWh a year, which cost me about 60 Euros in Germany. With solution 2. I’m depending on my PC again. If I wanted that, I would have bought a Flex.

Why use that large PSU for powering a switched-off IC-7300 that requires only 45mA? Why not use a small SMPS to power the IC-7300 in off-mode to keep the clock running. Don’t need an Arduino for that, an automotive relay is sufficient. You can buy a 12V/40A type for a few Euros. Connect the coil to your large PSU and switch the 13,8V input of your IC-7300 between normal PSU and stand-by PSU. I repurposed the SMPS of my old WRT54 modem (the little grey box) as stand-by power supply. That small box consumes about 0,5W when “powering” a switched off IC-7300 and I’m reducing yearly cost from 60 to 1,5 Euros. Such a SMPS is build to be powered-on all the time.

What about relay contact resistance? You’ll be amazed how much info can be found on-line regarding automotive relays. I measured an additional 0,16 V drop with 18 A due to relay contacts, FASTON terminals (crimped, not soldered) and 10 cm extra wiring. This translates to less then 10 mOhm contact resistance, which corresponds to relay specifications. Nothing to be worried about. And there is more…

Not only the clock circuit is powered when the IC-7300 is switched off, but also the USB hub, serial port UART and Audio Codec. Result: no more changed audio device issues on Windows! No more changing serial device names on Mac!

Beware of old-style transformer based wall-warts. Their output voltage is very often not or not properly regulated. I measured 16 V (without load) out of such a device that was labelled 12 V…