I just might do that, it's an excellent piece of advice, never crossed my mind! 🙂
I will post back the outcome....

Thanks, it obviously made a difference. Also, the radio is now able to tune to a station without the antenna wire attached and stay at the same volume. This is how my working unit behaves, too. Before, the volume level depended on the presence of antenna.

I have little to no choice when it comes finding someone else to tune this properly, there simply aren't any repair workshops in my town that deal with electronics this old that I know of. I can partially understand that, as some specific parts are impossible to find anymore. But still... 😔

I couldn' find exact data...

I managed to assemble the T4 and solder it in. It does influence the volume, I can tune it to a very narrow specific position when the FM volume is the highest. It is not as high as it is supposed to be - but seeing that turnig T4 influences the volume tells me all its pins are now in contact. Still, I am doing this while the radio is tuned to a station. The service guy obvously tried to set all the trimmers as they were all in different positions compared to the image I took before bringing the radio to him. So I am setting them randomly, stopping when volume/reception is best but likely not...

Thanks, I hope it will make a difference.
I talked to him today, he said he pulled it out that way. To be honest, I think this T4 part may have been removed and opened before, at the previous owner's. One coil wire was torn, while the other one was unsoldered, but was actually an extension wire going to the cap. The capacitor obviously had elongated wire endings on each side, which the factory wound all the way to the respective pin. On one side this is the case, but on the side where the missing pin is, there was a solder blob on the capacitor's end with an extension wire soldered on. Plus,...

I have managed to mend the missing pin by using the same thickness lead of a resistor. I then used a string of copper wire for bridging the missing piece. I made very tigh latching hooks on the end of each wire and hooked them together tightly, then soldered. I then soldered the extended wire around the new pin and back up to the capacitor's end. It took me almost two hours to thread this and solder it, the think wires were a pain to deal with.
Now it reads continuity between all the pins, so that's a good sign for now.

I have no idea what the "cap" part inside is,...

I desoldered and opened the can. Two wires are detached and the pin itself is completely missing, as if it wasn't in there to begin with as there are no flux, solder nor heat traces around its hole.

So, only one wire goes to the coil, the other one is just a bridge to the capacitor. I cut a fresh lead and it inserted into the hole firmly, which means the hole isn't cracked or something. I now just need to figure out how to extend the otherwise very thin and short wire to the pin and then to the capacitor end....

OK, guys, here is the thing. As suggested by Agent24, I checked the center tap on T4, and here are the results:

* - *
* * *

The "lower" coil, which has a center tap, reads continuity between the center tap and the right one. But, between the center tap and the left pin, I get no continuity, only resistance. It dances between 17 and 50KΩ for a second or two and then settles at ~27KΩ. But when measured across the left and right pin, it settles at 24-25kΩ. It seems that something between the left pin and the center tap is bad, plus it now rules out the...

Thanks, Agent24, that sounds assuring. OK, I will check those two parts of the coil separately. After reading your comment, I realized the center tap is actually marked with a black dot (I didn't know that 🥴). I will take another measurement and recheck the rest of the coils which also have a center tap and report back. I really hope we're on to something here. 🙂...

I checked the coil connection pads on T1, T3 and T4. All pass continuity check, but on T4, one coil passes, and the coil which is in parallel with the small internal cap doesn't show continuity, but I get a 25kohm reading berween its contacts (see the red line in the picture). I did this in-circuit, unpowered, but can this indicate anything substantial? Should I desolder T4 and attempt to open its can to inspect it inside? Do you think a fault in this area could weaken the signal strength/volume?...

Yes, that thought has crossed my mind, too. While they are unsolldered from the board, I will check the continuity between the pins where wavy coil line is drawn in the manual and hope I will find a broken continuity, to have something to start with. If one emerges, I will then attempt to lift the can and inspect inside. If nothing else, maybe I wiill pinpoint the exact transformer that has gone bad, and hope not all three are be faulty (or perfectly fine, in which case It will become quite unnerving)....

I think I got the markings correctly and cross-referenced them with the codes in the service manual. Take a look and let me know if I got it right. Here are the full labels in the manual, the bold parts are numbers printed on the body of each respective transformer:
T1: 1-405-685-00
T3: 1-404-144-00
T4: 1-403-953-00

This still doesn't tell me their values and stuff, but maybe you will recognize the type of transformers and know an equivalent alternative....

I took the radio back today and the guy replaced 5 electrolytic capacitors, two disc-like one, the IC01 circuit and a transistor. The capacitors he replaced had current problems. He explained to me that he attempted to tune the IF several times, but got different an incisistant readings and low volume, which finally narrowefmd down to these IF transformers. Also, he suggested that all three FM-involved Ts be replaced as there may have been corrosion inside or other process that may have damaged the tiny coil(s) inside or the ferrite core. Now, since I don't know the previous history of the radio,...

Yeah... I've watched a video on that. But that sounds like a shot in the dark for me. I wouldn't know how to disassemble one, let alone repair it. And, the service manual only shows symbols for what's inside those small transformers (coil and capacitor symbols), but they are all marked only as "internal components" with no value whatsoever.
So, my option is to buy the most similar ones and try with them.

So, let's see, T1 is a 455Khz FM trap?
T3 and T4 are likely 10.7Mhz IF, as they follow the ceramic filter at 10.7Mhz?...

We shall try and find equivalents. I guess it would be wise to have these in spare as one can never tell if, or when, any in the other unit may fail. I remember we had a few old FM radios which, if only we had know better, ended up being collected for recycling. They may have had these parts inside, but now it's all gone. I also wouldn't use a perfectly working unit as a donor device just so its part might fix this glitchy Sony radio.

The AliExpress link Agent24 sent seems to have various value transformers, and I shall have som assistance with which are the exact equivalents to the...

Yes, those three. The fault seems to be at T3 and T4. I saw the video he showed me, wiggling or pressing their pots/leads impacts the volume to increase as a certain angle is hit while wiggling or pressing. Maybe something got detached inside them, I don't know what the device had suffered at previous owner's.

T1 is the darkish red looking one, close to Q1
T3 is the yellow one
T4 is the blue one (these two are next to each other and close to IC01).

Hi, all.
Sorry for the long delay, but there were some things that needed to be done. In the meantime, the service guy has found the fault with the radio, but claims he cannot find spares due to age (which I believe is so), nor does he have a donor device with the same parts to take from, again, due to the age of the electronics at hand.
However, he removed these three suspected components and sent me the images. These are, I believe, the FM transformers and something you had also suspected to be at fault.

Could you take a look at the images and help me find equivalent...

Hello, people.
i am not sure if this question belongs to this forum section exactly, but since there already are some queries here about power transformer, let's give it a try.

So, I have this old but very well preserved Casio SA-20 ToneBank keyboard. It is powered either by five 1.5V AA bateries, or via a power adapter, so its operating voltage is 7.5V. The power adapter input jack also states 7.5V DC In. Now, since this keyboard was never supplied with a PT, but actually came with test bateries included, I decided to try to buy an adapter for it. I know I could have just gone...