Vintage SONY Digital Clock Radio ICF-C12W no audio

[UserXP]

In the meantime, I converted the display to 24h mode. Pins 41 and 42 power the AM and PM symbols on the display. So, I cut the traces near the solder pads where VFD pins for the two are, and used small jumper wires to connect pin 41 to the VFD pin for the lower segment of digit 1, and pin 42 for the rest of the segments which together with pin 40 form digit 2.
i also connected the "H" joint for the chip, this should enable it to count the hours beyond 12 and up to 23 now. Hopefully, it will work.
What do you think about this feat, does it look OK to you? 🙂

Now, since the display board and its two quite rigid and tight cables are out of the way, is there a way to temporarily "jumstart" the radio without the function board? Do you think it's possible to feed Q7 a required voltage from the main board so it activates the radio? That way, if you suggest replacing or removing a component from the main board, its maneuvering should be a bit easier.

Also, I've been thinking, I really hope the previous owner who had done work to the radio didn't change any of those Tx coils. If they are offset, could that cause low FM volume (just a layman thinking)?

[UserXP]

If it's not possible to switch on the radio without the function board, I will then attach it. I was thinking, would it help if I could attach a video (a temprary YT link or so) so you could see and hear the FM reception and volume compared to AM? Would that help?

[R_J]

Likely the easiest way to run the main board would to just short across Q7 Emitter to collector, that just completes the ground circuit so the radio should be on all the time when power is applied.
the other way would be to connect a 4.7KΩ or even a higher value would work from C36 (12VDC) to Q7 Base, that would also turn on Q7 to conduct
I doubt anyone has played with the coil etc. adjustments, if they did AM would likely not work as well and FM would not just be low volume but out of tune completely. Make sure you have a good length of wire for the FM antenna, the circuit is fairly simple so there is not much to check without having a scope to check signal amplitude

[stj]

maybe Q1 is bad,
the antenna cable makes it vulnerable to static/emp

[CapLeaker]

Got an oscilloscope? Measure the audio input at the volume knob or slider. Compare it to a working one. Problem can’t be C30 or C44, as it would affect AM as well. So you got anything in from the IF, the FM detector ending at R18.
How this works is that dial frequency is converted to a single intermediate frequency (IF) which is fixed and sitting on 455khz.

[UserXP]

Got an oscilloscope? Measure the audio input at the volume knob or slider. Compare it to a working one. Problem can’t be C30 or C44, as it would affect AM as well. So you got anything in from the IF, the FM detector ending at R18.
How this works is that dial frequency is converted to a single intermediate frequency (IF) which is fixed and sitting on 455khz.

I have no idea what you've just said, me being a layman in electronics. 😃🥴 But, I don't have an osciloscope, just a simple multimeter and an ESR meter. So, we'll have to try some other way. 🤔

R_J, you are a guru in this! Yes, bridging Q7 E and C pads does turn the radio on. So now it will be a bit easier without the function board dangling and constricting movement with its cables.
Now, I also believe you are right about the trimmers. I found and older photo of the working unit main board's top wiew. The "-" grove on top of each Tx part is oriented almost exactly the same as on the unit we are repairing. Plus, like you said, the AM volume isn't affected, so they ought to be good.
So now we just need to find that final culprit. So far, we have:
1) replaced the capacitors and woke up the radio unit, which had been completely dead.
2) removed, checked and confirmed that rectifying components and some other parts are good and operational.
3) fixed the low voltage problem (big thanks for this one)!
4) converted the display to 24h mode (successfully, I hope, but I followed the pins' function in the manual, so we'll see). 🙂

Stj, how can I test Q1, there is little data on its voltages? I guess I could test it in diode mode to see if it is OK. What do you suggest should be expected readings on Q1?

The antenna is not soldered, I removed it because it's a ~12 inch long piece of wire and it would be in the way. But, I remember when I completely disassembled the working unit a few years ago, it was perfectly cabable of capturing the FM signal at the same loudness and clarity as with the antenna attached, it was just more under the influence of moving objects, position and so on (it would have faded or fluctuating signal, but it played a staton perfectly).

Pending to fix is the low FM volume. Thank you all for wanting to help and for being patient with me, I really appreciate your willingness to help me repair this great piece of history.

[UserXP]

OK, guys, I checked Q1 and Q2 in diode mode, they appear to be NPN, positive (red) probe is on the base. They are bith 2SC930. Radio is switched off.

On Q1 (FM mix) it looks OK:
B to C =0.74V
B to E = 0.74V

Now, on Q2 (FM OSC), the readings in diode mode are:
B to C = 0.00V (but passes the continuity check)
B to E = 0.70V

Is B to C influenced by other components and is giving 0V because of that, or is it open? I really hope it is OK, because removing Q2 would be a pain in the neck.

[CapLeaker]

If the FM oscillator and the FM mixer wouldn’t be working, the FM band would be dead and hear nothing.

[UserXP]

If the FM oscillator and the FM mixer wouldn’t be working, the FM band would be dead and hear nothing.

OK, that means we can rule out bad Q1 and Q2, as well as misaligned Tx coils, then. 🙂

[stj]

are we using the c11 manual or the c12?

[UserXP]

are we using the c11 manual or the c12?

The only manual I have is for ICF-C12L. It is the same model by look, but inside the manual, the AEP version matches my radio the most when it comes to PCB layout. My radio is model ICF-C12W.
The image attached is for ICF-C12L AEP model, it has FM and LW setting, but the board layout is exactly like the one in my radio.

[CapLeaker]

OK, that means we can rule out bad Q1 and Q2, as well as misaligned Tx coils, then. 🙂

Misaligned FM Rx coils could be, but I doubt they are that far out, unless someone stuck a metal screwdriver in it and made adjustments which is a big nono.
The alignment procedure is a delicate thing, unless you know exactly what your doing.

[UserXP]

Misaligned FM Rx coils could be, but I doubt they are that far out, unless someone stuck a metal screwdriver in it and made adjustments which is a big nono.
The alignment procedure is a delicate thing, unless you know exactly what your doing.

Yup, I saw the procedure in the manual and it is a multistep process of measuring voltages repeatedly in different tunning. That would be very complicated for me, so I really hope nobody touched those. Their tops look untouched and in similar positions like in the working unit's old photo, so I truly hope they are OK, especially since AM volume works fine.

Is the output sound coming out through IC01? Because, after that, it looks like it passes carrying sound from FM and AM equally through other components, through the volume knob, tranzistors and out through a capacitor. What can we try next?

[Agent24]

Not exactly, I believe the audio comes out of the FM detector circuit of T3, T4, D5, D6 etc.

Since you already checked voltage at IC1 Pin 7 and it looks probably okay, I don't know what else to say.

You could compare it with Pin 7 on the working unit, I suppose.
The schematic says 4.2v but you got 4.57v
I don't know if that's different enough to indicate a problem.

Unless there is some faulty part in the FM detector circuit, bad diode or capacitor maybe.


Measuring the diode drop on Q1 and Q2 won't tell you if it's degraded by ESD damage, generally.

The 0v reading (which would indicate a short circuit) across Base-Collector of Q2 is probably fine since you have R3 and L3 between those pins.
R3 is very low value of 3.3 Ohms, and the L3 will look like a short to DC as well.

[UserXP]

Not exactly, I believe the audio comes out of the FM detector circuit of T3, T4, D5, D6 etc.

You could compare it with Pin 7 on the working unit, I suppose.
The schematic says 4.2v but you got 4.57v
I don't know if that's different enough to indicate a problem.

Unless there is some faulty part in the FM detector circuit, bad diode or capacitor maybe.

OK, I will atempt that. I put the working unit back togrther and returned it to the house kitchen (my mom likes it there because of the radio and convenient clock). Disassemblying this radio is not difficult, but reassemblying is quite fiddling as you need to wiggle the function board to lock between all the grooves for it, all while the cables and buttons are obstructing what you are doing. 😃

OK, I will first measure the voltages on IC01 in AM mode and see if there are any offsets like in FM. If there are, but AM volume is normal in AM, the differencies of 0.X volts apparently wouldn't affect the folume.
I will also take apart the working unit, again. For this step, please write everything you would like me to compare between the working and almost working units, so I wouldn't have to take it apart often. 😉

[Agent24]

I don't know for sure, I don't know enough about troubleshooting radio stuff in general. I think wait for someone else to chime in on whether that voltage being 0.37v different matters. I am going to assume it isn't. But then you can't always tell with just a voltmeter. It could be a sign of something weird going on but I have no idea for sure.

An oscilloscope and function generator would be very helpful here.

Another option of course is to swap parts with the working set and see what changes, which is a hassle, but maybe your only option at this point without better test equipment.

First though you could check out the components in the FM detector,
Assuming the input signal to the FM detector is normal (which we don't know for sure) then low audio signal could be caused by a fault with any of the following,
T3, T4, D5, D6, R12, R13, R15, R18, C23, C24.

For example, if R18 was high resistance you could get issues, if C24 was open circuit, if C23 was bad (though I think this is one you already replaced - but did you solder it okay?)
If either of the diodes was bad you could have problems, etc. I would check all the resistors and diodes and replace C24 just in case.

I also recall reading where the capacitors inside the coil cans can fail with age, although I don't think this radio is old enough that it's likely to be a problem, I think that's more with older valve era stuff, but it's still possible I guess.

IC1 of course could be bad, or perhaps the CF (ceramic filter). I've heard of those going bad before, in receivers.

[CapLeaker]

The FM DET makes the audio in FM mode. Before that everything is RF. Problem is we don’t know if the IF level is o.k. You need an RF probe, oscilloscope and an RF generator. Start looking at R18 and go backwards.