Vintage SONY Digital Clock Radio ICF-C12W no audio

[Agent24]

Thanks, Stj and CapLeaker. So, you don't think it's Q2. But, if I am to remove it and it turns out to be bad, I'd have to have a replacement part as there is no point in swapping them as I'd be still left with a faulty one in the circuit... Removing Q2 is something I don't how I'll manage to do. It is immersed in some kind of hardened paste. Can I buy a few 2SC930 transistors and just put the leads of the new one onto the pads where the existing Q2 is soldered? If the old one was bad, would the new one in parallel "take over"? This would save me the trouble of actually removing Q2 if it wouldn't be necessary - but, I am willing to try here whatever you guys suggest.
However, Q1 wouldn't be too difficult to remove.

If you do buy a new transistor you may find BF495 easier to get as a substitute. But be aware the pinout may be different.

[Agent24]

need a 455KHz source,
i wonder how cheap one can be made!

https://electronbunker.ca/eb/SignalGen455.html ?

[UserXP]

Thank you, all. Yes, I found a list of substitutes/equivalents of certain phased out components. While we were troubleshooting the low voltage issue, I found replacements for Q5-Q7, having the idea of changing them back then to see what would happen. There is a local electronics shop where I live and their website actually offers an available substitute part for the item searched. So finding a replacement locally isn't impossible.
I can buy some and try with Q1 first as it is easy to remove. I really hope it won't be in vain like with other unsoldered original components that turned out fine - which would leave us with no solution yet. I still hope for that "Aha!" moment. 🙂

[stj]

you could "borrow" parts from a working radio to see what actually is needed

[UserXP]

you could "borrow" parts from a working radio to see what actually is needed

Nnno... I wouldn't want to disassemble it that far. I fear I might end up with two inoperative units. 😃
it is safer for me to buy a few of those transistors and see if they would change anything in the faulty unit. 🙂

[UserXP]

I checked the soldered Q1 and Q2, they are 2SC1675 IF signal amplifier.
I found these equivalents: BF241, BF255 and BF495 as Agent24 has already suggested. I also found 2SC930 new old stock.

[UserXP]

OK, this is the C930 that I was able to find. Will it match for Q1, should I go with the replacement?
Also, how to check which pin is E and which is C? I know I can determine the base, it should have positive to negative probe voltage drop of ~0.7V to both C and E. There should be no flow between C and E. But how will I know which one is which?
This transistor is flat on both sides.

[Agent24]

OK, this is the C930 that I was able to find. Will it match for Q1, should I go with the replacement?
Also, how to check which pin is E and which is C? I know I can determine the base, it should have positive to negative probe voltage drop of ~0.7V to both C and E. There should be no flow between C and E. But how will I know which one is which?
This transistor is flat on both sides.

If it's the same model as the old one, it should be the same pinout.
The text marking should be on the same side.
So just put it in the same way around as the original one, with the text facing the same way.

Otherwise, you can check with the datasheet, which will tell you the pinout.
In the datasheet stj posted, you can see the pinout.

Yes the case is flat on both sides but there is a bevel edge on one side, that is how you can reference the pinout.

[UserXP]

This radio is driving me crazy. I found 2SC930 transistors. But the ones soldered at Q1 and Q2 are 2SC1675. Thinking that they are interchangeable, since the manual offers one, I went for it. And - the radio doesn't sound any different even with C930 soldered.

I also tested the removed one, 2SC1675, it seems OK. Voltage drop is about 756mV from B to C and 761mV from B to E. This appears normal, right?

I wouldn't be surprised if yet another original component turned out to be fine. What a bunch of dead ends this radio is throwing at us! 🙁

[UserXP]

Is it possible to test the signal frequency with the Hz setting on the multimeter? Can we test the CF that way?

[CapLeaker]

In one word: nope.

[Agent24]

This radio is driving me crazy. I found 2SC930 transistors. But the ones soldered at Q1 and Q2 are 2SC1675. Thinking that they are interchangeable, since the manual offers one, I went for it. And - the radio doesn't sound any different even with C930 soldered.

I also tested the removed one, 2SC1675, it seems OK. Voltage drop is about 756mV from B to C and 761mV from B to E. This appears normal, right?

Normal for the basic diode-junction test, yes, but that will only show you if the part is short or open circuit.

It won't tell you if the transistor is degraded, if the junctions are leaky, or anything else.
For that you would ideally want a curve tracer.

Some multimeters do have a basic DC gain/HFE measurement function, but that won't tell you if the gain is degraded at high frequencies, which is important in an FM circuit.

But anyway, if you replaced it with a brand new one, and got no change, then probably the original was okay, and the fault lies elsewhere.

Is it possible to test the signal frequency with the Hz setting on the multimeter? Can we test the CF that way?

Not unless your multimeter can measure over 10Mhz frequencies, which I highly doubt it.

In any case, you could just buy a new filter from AliExpress or such, they are cheap there, if the filter has drifted in frequency or is outputting low amplitude maybe it would cause this problem? (again, I don't know enough about radio circuits to say for sure), although other parts are probably more likely to fail - I think it was the lower-frequency ceramic filters that sometimes go bad - but yours is crystal so less likely. Still not impossible though.

An oscilloscope would be great at this point, but if you don't have one, I think the only real option is to start swapping parts until you get lucky.