Hi all, I have SONY Dream Machine ICF-C414, it runs about 1 minute fast per month. I opened it up and found 2 variable resistors. Can anyone explain how they need to be adjusted to compensate the drift? Here are 2 pictures of the resistors:

 

Your photo shows two variable inductors (not variable resistors) for aligning the radio.

A clock radio usually has a counter circuit driven from 50Hz or 60Hz of your electricity. In Europe and North America it is usually very accurate but other places are not accurate which might be your problem.

If your clock radio has a battery then it is used to keep the clock running when the electricity power fails. It might have a variable resistor to adjust it but usually a very accurate crystal in an oscillator circuit is used.

 

Your photo shows two variable inductors (not variable resistors) for aligning the radio.

A clock radio usually has a counter circuit driven from 50Hz or 60Hz of your electricity. In Europe and North America it is usually very accurate but other places are not accurate which might be your problem.

If your clock radio has a battery then it is used to keep the clock running when the electricity power fails. It might have a variable resistor to adjust it but usually a very accurate crystal in an oscillator circuit is used.

Ah thanks for the info. I am in North America. There are no power interruptions. I looked around the board more and see this clock crystal, dont see anything to adjust it... can I maybe replace this crystal with a better one?

Its right next to the radio speaker, would magnets from the speaker create interference with the crystal?

 

Sorry looks like I cant edit above post, so I have another question. If I do replace it with another crystal from Digikey or something, does it have to match frequency? Yes right? How do I find out frequency of this crystal? It has no other markings other than the KOSOL seen in picture.

 

The speaker magnet does not affect the clock. Most clocks use the 60Hz to accurately run the clock, the crystal is used during a power failure. I think your 60Hz has a very small error.

 

The speaker magnet does not affect the clock. Most clocks use the 60Hz to accurately run the clock, the crystal is used during a power failure. I think your 60Hz has a very small error.

oh, you are saying its getting 60Hz from the grid? Is there anything I can add to the circuit inside the clock to "filter" it to make it more accurate? The thing is. I have another Sony clock, also Dream machine, but different model (a few years older) and that one runs perfectly wihtout ever drifting in the same house (so same grid).

 

Maybe your clock is picking up some interference from the grid due to a poor clock design. It would be difficult to find and fix the device causing the interference. You might not find the schematic and parts list to fix the clock with a circuit that does not have the problem.

 

1 minute per month is 23 ppm, which is about the tolerance of that kind of crystal. So, I suspect the clock is running off the crystal always. Perhaps it is designed that way, or else the circuit to determine that the crystal should be used is failing.

There should be two small capacitors near the crystal that could be trimmed to improve the accuracy, but I don’t see them in the picture.

 

I agree with BobTPH, if two identical clocks run off the same AC power and one drifts and the other does not, then it seems that the circuit feeding the 60Hz pulse to the clock circuit has failed, somehow. Or, the processor reading the 60Hz pulse has a failed input pin (difficult to fix).
Comparing the signals at the clock "cpu" with a scope would show any differences when looking for a 60Hz signal.
Also, look for cold solder joints. Those types of PCBs tend to get them with aging of poor solder joints.

 

Gaining time suggests a noisy power line, though I agree this looks like the crystal is not well trimmed. If you can identify ground for that circuit, you can probably slow the clock down by putting a very small capacitor (5 to 10pf) from one end of the crystal to ground. Which end? I can't tell, but either will probably slow down the clock. After adding the capacitor the clock might stop, but I doubt it will, then wait a month and see how much correction is still needed.

Edit: Replacing the crystal is a dice throw - it might make the situation better or make it worse. Most likely the crystal in there now has not been trimmed to reduce the error.

 

thanks all for replies. It seems like it gains about 1 second every 24 hours. I set it to time.is yesterday, then 24 hours later did the check and it ticked over when time.is was at 59 seconds. The other Dream Machine (its not exact same clock, both are SONY dream machine but different models), the other one is still spot on 24 hours later. They are in different rooms of the house in case line frequency can differ between rooms, its probably different circuit.

I can test if crystal is used when wall powered (as opposed to keep time when no power) by disordering it. Should I try and put a different crystal in its place? If so, which one?

It seems like since its off 1 second approximately every 24 hours its easy to test (dont have to wait a month).

You guys are mentioning trim on the crystal. How can I trim it? or is that programmed into the SOC and cant be messed with?

Im not trying to achieve atomic clock levels here Im just trying to get it to not be off by a minute after a month

 

also, I am assuming that if thats an 8Hz crystal, and I put in a 16Hz crystal then it will run at double speed (30 minutes in an hour?). So I need to match the crystal frequency of existing one? Im also wondering if perhaps the SOC uses this same crystal for it's own clock? meaning faster crystal would overclock it?

Unfortunately I do not have a scope, so will have to do this blind/guessing. Unless someone can identify that crystal?

 

The crystal is a 32768 Hz watch crystal. As I stated before, the clock is running with the accuracy expected from the crystal. So replacing it would not likely help.

@DickCappels told you how to trim it in post #10. Add a small 5 or 10 pF cap from one lead of the crystal to ground. This is purely guesswork. Or, the better way to fix it would be find out why it is not being run by the line frequency., but that would not be easy without a schematic.

It will never stay in synch with the other clock unless they are both run off the line frequency. Line frequency is adjusted up and down by the utility to make clocks stay synchronized to the actual time. A crystal cannot do that.

 

If you are in USA and the clock is not keeping time then something is wrong.
60Hz line frequency is adjusted daily to get the correct number of AC cycles each day.

Presumably the 60Hz time-base circuit is not working and it is running off the 32768Hz xtal oscillator.
One thing to try is to disable the xtal oscillator by putting a 0.1μF capacitor across the xtal. If the clock stops advancing then you know where the problem lies.

 

If you are in USA and the clock is not keeping time then something is wrong.
60Hz line frequency is adjusted daily to get the correct number of AC cycles each day.

Presumably the 60Hz time-base circuit is not working and it is running off the 32768Hz xtal oscillator.
One thing to try is to disable the xtal oscillator by putting a 0.1μF capacitor across the xtal. If the clock stops advancing then you know where the problem lies.

The reason I thought maybe replacing oscillator would work if maybe there is variance in manufacturing? Presumably manufacturer used the cheapest one possible that may have higher tollerances?

If I determine that its running off the crystal, what are my options in fixing that? What are the chances it was designed to run off of the oscillator and not line frequency?

This is the clock "service manual" but it doesnt provide any info on anything - https://servicemanuals.us/sony/audio/icf-c414.html

 

Maybe that "Dream Machine" was made for a country that does not regulate the 50Hz or 60Hz frequency of their electricity, then the crystal oscillator is used all the time..
How does the Dream Machine know if the electricity is 50Hz or 60Hz? It measures it?

 

The reason I thought maybe replacing oscillator would work if maybe there is variance in manufacturing? Presumably manufacturer used the cheapest one possible that may have higher tollerances?

If I determine that its running off the crystal, what are my options in fixing that? What are the chances it was designed to run off of the oscillator and not line frequency?

This is the clock "service manual" but it doesnt provide any info on anything - https://servicemanuals.us/sony/audio/icf-c414.html

Go back and read my post #13, where I answered these questions. If you don’t understand the aswers, tell us what is confusing you instead if simply asking the same questions over and over again.

 

Maybe that "Dream Machine" was made for a country that does not regulate the 50Hz or 60Hz frequency of their electricity, then the crystal oscillator is used all the time..
How does the Dream Machine know if the electricity is 50Hz or 60Hz? It measures it?

In the manual it says to use on power specified on the back, not clear if its saying 60Hz or 110V. Or both.

Go back and read my post #13, where I answered these questions. If you don’t understand the aswers, tell us what is confusing you instead if simply asking the same questions over and over again.

Well, I understand the use of cap to slow down the crystal. My question was regarding fixing it so that it uses the grid 60Hz instead of crystal.

 

Some more PCB pictures

 

I circled the legs of the crystal (K252)