Sony ICF-C12W Radio Clock schematics (power)

[UserXP]

Re: Sony ICF-C12W Radio Clock schematics (power)

yes,
remember, in 110v country's the voltage can vary by atleast +-10v so 100-120v
and in 220v country's the allowed variance is worse - 220-250v

the transformer output will vary with it's input so the clock has to be designed to operate over a reasonable range

OK, that sounds great. I didn't observe any overheating or bad voltages. I checked the line that powers the OKI chip, the voltage is about the same or slightly lower than it was with the original power transformer which was run on a 220 to 110 volts power converter. The clock is operational, it shows quite an aqurate time, the radio sounds clear, no crackling, buzzing, humming or any other unwanted noise, the reception is great, so it seems it will work OK.
I also measured some of the filtering capacitors in there. The biggest filtering cap is Elna 16V1000uF, others seem to be Lelon or something like that, the letters are too tiny for me to see. But they all measure within their ratings, even after 40 years of age.
I wish I could see a modern device today lasting up to 40 years with no required service. In the past, things were built to last. Now they seem to have a planned obsolescence with a built in expiry date.

Thank you, guys, for helping me fix another piece of great equipment, this old-timer digital clock radio from Sony. Cheers!

[stj]

Re: Sony ICF-C12W Radio Clock schematics (power)

yes,
remember, in 110v country's the voltage can vary by atleast +-10v so 100-120v
and in 220v country's the allowed variance is worse - 220-250v

the transformer output will vary with it's input so the clock has to be designed to operate over a reasonable range

[UserXP]

Re: Sony ICF-C12W Radio Clock schematics (power)

After a couple of hours of testing, I think this may turn out to be a good conversion. For reference, here are the previous readings with the original PT.

A for black (center tap)
C for one red wire
D for the other red wire.

The voltage between A and C is 5.7V.
The voltage between A and D is 5.9V.
The voltage between C and D is 11.7V

New readings with the replaced PT are:

A for black (center tap)
C for one yellow wire
D for the other yellow wire.

The voltage between A and C is 5.73V.
The voltage between A and D is 5.74V.
The voltage between C and D is 11.4V.

Do you think these voltages will be OK on the long run?

[UserXP]

Re: Sony ICF-C12W Radio Clock schematics (power)

Here are the results. The replaced transformer provides ~0.2 lower voltage now that it is loaded than the original one did.

I used a replacement cable clip as the original one was broken.

I connected the input power to the PT with a joint. It is neatly fixed with an M3 screw which conveniently is placed in the hole next to the 220-240V marking - excellent as an input voltage indicator on the back.

I reattached all the wires. The little grey flat cable was especially challenging to solder without melting it, but it turned out great.

The tunner mechanism was too complicated for me to dismantle so I simply taped the string to its rollers so it doesn't unwind and then freed all the guides and rollers. It was worth it, plus it retained original indicator position.

It has been playing radio for the past two hours, works great. More testing and images coming soon.

[UserXP]

Re: Sony ICF-C12W Radio Clock schematics (power)

Update:
I found a 230VAC transformer that outputs dual 5.5V, it arrived today. It is also shielded, so it could have come from some audio equipment, which is a plus (it's used, but in good shape). Upon measuring its terminals without load applied, it actually outputs 5.7V on center tap and 11.4V total. So it seems to be within the measurements taken from the radio clock unit. Hopefully, it will help converting the unit to work with 220V mains.

[stj]

Re: Sony ICF-C12W Radio Clock schematics (power)

5-0-5 then.

[eccerr0r]

Re: Sony ICF-C12W Radio Clock schematics (power)

Well you got your answer now, go get something that matches when you feed it your desired input voltage and fits in the allotted space!

[UserXP]

Re: Sony ICF-C12W Radio Clock schematics (power)

This is measured exactly at the point the three output wires are soldered onto the PCB. The rotary switch was set to OFF, only the display switched on.

[UserXP]

Re: Sony ICF-C12W Radio Clock schematics (power)

I measured it.

On the diagram, these wires are labelled:
A for black
C for one red wire
D for the other red wire.

The voltage between A and C is 5.7V.
The voltage between A and D is 5.9V.
The voltage between C and D is 11.7V.

This is with load applied as the device turns the display on immediatelly after powering on.

I suppose we need to achieve the 5.7 and 11.7 values (although, according to schematics, they should be slightly lower). But then again, it is powered through a step down converter, maybe it's not producing 110-120V precisely.

Do these measurements help? Attached is the size of the transformer.

[eccerr0r]

Re: Sony ICF-C12W Radio Clock schematics (power)

Again you have a multimeter, measure the voltage, go from there. Don't want to hook up your filament and have it burn out, might well throw out the whole clock if this happens...

[UserXP]

Re: Sony ICF-C12W Radio Clock schematics (power)

The original transformer is likely closer to a 10v CT, 5-0-5, this will give you around 13VDC. The AC voltage listed for the transformer is not the same as the DC voltage after it is rectified and filtered.

Thanks. If that's the case, then teplacing it wil be "go to eBay and search", which would bring Chinese sellers whose pictures of the products are usually generic/stock, plus the 50 day long shipping.
The lowest dual output PTs I can find in a local electronics shop is 6-0-6. :/

[R_J]

Re: Sony ICF-C12W Radio Clock schematics (power)

The original transformer is likely closer to a 10v CT, 5-0-5, this will give you around 13VDC. The AC voltage listed for the transformer is not the same as the DC voltage after it is rectified and filtered.

[UserXP]

Re: Sony ICF-C12W Radio Clock schematics (power)

Chances are if it's 12V center tapped, the center tap would be 6V and way too high for the heater.

Could the marking T6-13CH on the original mean something like Transformer, center tap 6V, total voltage 13V, CHina? Maybe it's a 6-0-7, but Sony marked the two output voltages on it. In that case, a 6-0-6 12V transformer would provide the correct voltage for the 6V center tap, but slightly lower overall voltage (12V instead of 13V)?

The schematics also show the pin setup for the 24 hour mode. Pins 41 and 42 indeed need to go to different pins of the display, plus Pin18 to 11V connected. It looks tempting, but I would need to tear or break the leads and rewire the pins. It's just an idea, but the power transformer mod would be the priority, I don't mind the AM/PM symbols that much.

What are your thoughts on this PT label?

[UserXP]

Re: Sony ICF-C12W Radio Clock schematics (power)

I will check with my multimeter. I followed the traces, black wire is A, red wires are C (half voltage) and D (full voltage). I see that black goes through a resistor to the first pin of the display marked as F. Is that the filament (heater) contact you were referring to?

[eccerr0r]

Re: Sony ICF-C12W Radio Clock schematics (power)

Since you have the step down working, what is the voltage of the winding and tap?

[UserXP]

Re: Sony ICF-C12W Radio Clock schematics (power)

It is small. Maybe 2.5x2.5x4cm roughly. The longest dimension is the base with holes for being fixed to the casing with two screws. Based on its small size, it is probably a 5W, 2x0.125A or so. I'm just guessing.

[stj]

Re: Sony ICF-C12W Radio Clock schematics (power)

how big is the original one?

[UserXP]

Re: Sony ICF-C12W Radio Clock schematics (power)

try looking for a "bell transformer", 4.5v - 0 - 4.5v
aka 9v centertapped.

Bell transformers are what I looked for and found. The original PT is also of that type. It's the proper rating that needs to be selected.

[stj]

Re: Sony ICF-C12W Radio Clock schematics (power)

try looking for a "bell transformer", 4.5v - 0 - 4.5v
aka 9v centertapped.

[UserXP]

Re: Sony ICF-C12W Radio Clock schematics (power)

I didn't know there is a heating element inside. A heater?
So, could a resistor be inserted between the center tap 6V output to drop the voltage to the required 5.2V?
I guess the output voltage of the PT would also drop a bit after load is applied.

I found several PTs at a local shop which are dual 6-0-6 volts, a total of 12V of various VA, power and current. They are all 220VAC 50Hz input.
I tried leaving the clock radio running for almost six hours to test the clock. It works flawlessly after the Pin12 mod, but the rated 100W power converter I used became hot, even though it had just 5W of load applied. I wouldn't leave it running 24/7.

Any thoughts on this power modification? Schematics suggest output should be 11V and 5.2V center tap. That would seem to be a 5.2-0-5.8 transformer, right?