Vintage SONY Digital Clock Radio ICF-C12W no audio

[R_J]

R_J, I put the wires like you suggested, but I haven't attached the ribbon cable. I plugged the AC in and I, be prepared, still have only 7.64V.
The two anodes of D1 and D2 are connected by a trace on the board. I followed your advice with the C36 cap, but I get 6.1VAC on both anodes.
In DC mode, the C36 area reads 7.64V on the black probe.
This is without the function board attached.
Does this sound normal?

The way I drew it in post 91 is NOT THE WAY to have it connected, That is the WRONG way and that is why you are getting the WRONG voltages
How many times do I need to ask for the pictures?
You have it connected WRONG again and are now supplying 12vac to the filament instead of 6vac

[R_J]

Can you help me with how to wire the PT?
It has three orange wires coming out.
The first wire comes from where 0 is printed.
The second wire comes from the tap where 6 is printed.
The third wire comes from the tap where 12 is printed.
There is a sticker on the coils housing and this where the numbers are printed, right above each of the taps. The TP says it is 230VAC, 50Hz, 6VA.

0 is the center tap
6 supplies 6vac (referenced to center tap)
12 supplies 12vac (referenced to center tap)
So the 0 wire connects to Capacitor's negative , the 12vac connects to the diodes anode, the 6vac connects to the resistor that feeds the display filament

[UserXP]

0 is the center tap
6 supplies 6vac (referenced to center tap)
12 supplies 12vac (referenced to center tap)
So the 0 wire connects to Capacitor's negative , the 12vac connects to the diodes anode, the 6vac connects to the resistor that feeds the display filament

I really appriciate your help and I do apologize, but I'm doing the best I can. 😥 It is very difficult to take photos of components-side-up with everything connected because the wires from the PT are tight in length, the PT is mounted to the case and two speaker wires are also tight in length and the speaker is glued to the case. All this makes it very difficult to turn the board components side up because the cables restrict movement.

All wires from the PT are like 3-wire orange ribbon cable, all identical. I now see that the cable must have twisted around its axis and ended on the board in the opposite way while moving it over, so I must have overseen it when I threaded the wires through holes, my fault. It is very tight and almost impossible to maneuver the wires through the three holes and not have them pulled out while turning the board again to solder.
i hope the display is fine as it was on for maybe half a minute while I was measuring the voltages when I noticed the three bright heaters inside and immediately unplugged the AC cable. It is quite late here now so I will recconect the wires tomorrow the way you illustrated. 😊

[R_J]

I really appriciate your help and I do apologize, but I'm doing the best I can. 😥 It is very difficult to take photos of components-side-up with everything connected because the wires from the PT are tight in length, the PT is mounted to the case and two speaker wires are also tight in length and the speaker is glued to the case. All this makes it very difficult to turn the board components side up because the cables restrict movement.

All wires from the PT are like 3-wire orange ribbon cable, all identical. I now see that the cable must have twisted around its axis and ended on the board in the opposite way while moving it over, so I must have overseen it when I threaded the wires through holes, my fault. It is very tight and almost impossible to maneuver the wires through the three holes and not have them pulled out while turning the board again to solder.
i hope the display is fine as it was on for maybe half a minute while I was measuring the voltages when I noticed the three bright heaters inside and immediately unplugged the AC cable. It is quite late here now so I will recconect the wires tomorrow the way you illustrated. 😊

The heater should be ok, as there is a current limiting resistor in series which helps, You can leave that connection off for now if you like and just connect the 12v ac to the ground and diode so you can confirm the proper 11 vDC across the C36 cap.

[UserXP]

The heater should be ok, as there is a current limiting resistor in series which helps, You can leave that connection off for now if you like and just connect the 12v ac to the ground and diode so you can confirm the proper 11 vDC across the C36 cap.

R_J, I soldered it properly this time. 6VAC to the heater, Tap0 to capacitor negative and 12VAC to diode anode.
You did it, you solved the puzzle!!! 😊 The voltages on D1 and D2 cathode ends are now 14.9-15V DC in Radio mode on. In radio Off it is the same.
The bright switch now also works as intended, L illumination setting is now well visible and H setting is in very nicely lit cyan colour, just like on the working unit.
This is all good news!

Now, the volume problem with FM did not resolve, it is still very gradually increased and when on maximum, you can listen to it nicely only if you're sitting quite close to the radio. But it is generally a bit louder with the volume issue now fixed. The AM mode is fully loud after the voltage fix, just like it is on the working unit. On the working unit, FM volume changes in the same loudness increments as AM. If you were to set it to maximum, the whole radio case would start to resonate and roar. But on the "faulty" unit, only AM volume changes like that, FM is much quiter.
Any ideas what could cause this and what to check next?

Man, what a relief so far. I have dismantled this board so many times and removed various parts and we had some crazy results.
Now, the display displays the symbols normally, the power supply voltages are constant. If we could only resolve the volume also, it would be awesome.

[R_J]

Going by the service manual you provided, there should be a wire used as the FM antenna, it is a grey wire going from L1 to the CASE of the transformer, the transformer case is used as an fm antenna. If you can locate this grey wire, try touching it and see if the fm level increses.

[UserXP]

Going by the service manual you provided, there should be a wire used as the FM antenna, it is a grey wire going from L1 to the CASE of the transformer, the transformer case is used as an fm antenna. If you can locate this grey wire, try touching it and see if the fm level increses.

Yes, there was a white wire antenna. It was soldered onto the bottom right corner of the board, where the white "ANT" symbol is printed next to the solder pad.
i tried touching it with my finger or touching it with a screwdriver in upright position. The volume doesn't change. The sound is very clear, there is no hiss, crackling or other noise, you just can't increase the volume properly.

[CapLeaker]

check the FM IF amp circuit. Can't be the audio amp if AM works full bore.

[stj]

there are atleast 3 cracked solder joints in that picture.
almost there though

[UserXP]

check the FM IF amp circuit. Can't be the audio amp if AM works full bore.

You mean to check the voltages on each pin of IC01 amplifier?
But, for some pins, values are in brackets. What do they mean, do they read as such in certain modes?

[UserXP]

I turned the radio on at FM and checked the voltage coming from the FM setting on the switch. I will check the voltages on pins and post back.

[R_J]

You mean to check the voltages on each pin of IC01 amplifier?
But, for some pins, values are in brackets. What do they mean, do they read as such in certain modes?

At the lower left of the schematic page it lists what the voltages in brackets (xxv) AM (Function "ON")

[UserXP]

At the lower left of the schematic page it lists what the voltages in brackets (xxv) AM (Function "ON")

Oh, great, thanks for pointing that out. I am viewing the manual on my phone and when the manual's zoomed in to see the pages, I have missed that part.
Soo... what does it mean "detuned"? Am I to turn the tuning drum until there is no reception of any kind in FM mode (not even static) and then measure only the values without brackets (FM Function "ON")?

[stj]

fix the bad solder joints first

[CapLeaker]

You mean to check the voltages on each pin of IC01 amplifier?
But, for some pins, values are in brackets. What do they mean, do they read as such in certain modes?

Yes, IC1. Just check the FM IF , the CF, another IF amp through the fm detect ending on the volume knob.Gotta be somewhere in there if FM audio is way lower than AM. You can compare voltage readings with the working one.

[Agent24]

there are atleast 3 cracked solder joints in that picture.
almost there though

I agree, some of those joints do look a bit suspicious.

UserXP: The bad ones have a kind of ring around the lead, and aren't smooth all the way across
There are some just up from where Q1 is marked on the underside that look like that.

[UserXP]

I agree, some of those joints do look a bit suspicious.

UserXP: The bad ones have a kind of ring around the lead, and aren't smooth all the way across
There are some just up from where Q1 is marked on the underside that look like that.

I know, but some pads are not fully occupied with solder. I mean, the radius of the pad is bigger that the solder, making them look like there is a ring around the solder. When you suggested to check for the existence of cold solder joints, I tried pushing and wiggling each pad point with a cotton swab, it would surely have moved the desoldered pin enought to touch and make contact. None influenced the volume.
BUT, to rule this cause out or confirm it, I will reflux and reflow each of the solder pads and see what happens.
I will measure the voltages also and post back the results.

[UserXP]

OK, guys, I started measuring the voltages so far.
On IC01, I only measured the pins where the values in the manual were presented without marks (no brackets) as it is for FM, just like R_J pointed out. Pins 1-8 seem to be mostly for FM, pins 9-16 are for AM, so I didn't measure those.
Pin1 = 0.00V
In the manual, it looks like 13.6V, but it seems it was supposed to be (3.6V). It seems they didn't print the other bracket so the first one looks like "1", making the value appear as 13.6V. It is 3.6V for AM when I switched to AM mode.
Pin2 = 0.71V
Pin4 = 3.14V
Pin5 = 3.44V
Pin6 = 4.57V
Pin7 = 4.57V
Pin8 = 3.42V

Voltages on CF are like on pins 4 and 5, as they are interconnected.

Other than some minor variations in the voltages, the IC01 appears to be OK?

T1 FM IF T voltages (positioned in reference to the pins on the board layout:
0.00 2.43
0.00 2.41

Please don't mind me using the board layout image as orintation as it is easier for me to identify the pins that way. 🙂

[stj]

these

[UserXP]

these

OK, I added some solder on those and several other pads that had a thin layer of old solder around the leads.
Then, I desoldered the volume knob pot and took it apart. It was full of dirt. I cleaned the slider contacts and the surface of the pot with contact cleaner spray. I put it back together and now I don't have those "gaps" of sound in random positions like it was before. So at least that is fixed.
But after all this, the FM volume is still much lower than AM.
I also noticed that, if I attach a wire or put a screwdriver on the antenna pad, the FM sound increases a bit, but it is still much quiter that it should be.