Chosen Solution
Hi everyone - my ICF-C1 clock radio runs fast, gaining about 1 minute and 20 seconds every month. I cannot locate a schematic for this clock radio, so I am unsure if I can modify an RC/crystal circuit to adjust the timing or whether this uses the 60hz mains frequency as a reference. Has anyone had any luck in locating a schematic diagram or in replacing a resistor or capacitor to have more accurate time? Technician with 30 years experience here, just looking for a diagram or helpful advice. Thanks, Rick
Hi @ricketts223 , Don’t know if this is helpful, but here’s a link to the service manual that whilst in itself is not helpful, there are links at the bottom of the page to the service manuals for other ICF C1xx models. A quick glance through a few of them, shows no mention of a crystal oscillator module in the parts list, so it may be that the mains frequency is used for the time reference. Hopefully yours is the same Note: You can view the manuals online but you need to select the next page at the bottom of the page to move through the manual. To download you have you sign up to the website.
You can’t really fix this - I have the same clock and the problem is that Sony was too cheap to use a proper IC that tracks the time via the AC mains frequency (which power companies go to great pains to ensure averages exactly 50 or 60Hz over time). Here Sony is using a generic 8-bit microcontroller and running the clock off the base time-of-day counter w/out an RTC and w/ the lithium battery as a backup power source. You can find the datasheet for this by searching the sister part number LC87FBG08A (with a different footprint), for example the datasheet is available via Mouser: https://www.mouser.com/ProductDetail/ons… There is an onboard crystal oscillator (part S3X1, X2 on the PCB schematic) supplying the 32.768K oscillations. The best accuracy that can theoretically be achieved is ±20ppm at room temperature (~10.34 minutes gained or lost/year), but with the temperature swings on the board it’s going to be worse than that. An option which I haven’t tried is to replace the XTAL with a DS3232 TCXO. Someone else figured out that you can add the TCXO instead, though your results may vary. Sony’s entire circuit is an exercise in cost savings and I cannot recommend using any Sony ICF-XXX clock to accurately keep time.
