Vintage SONY Digital Clock Radio ICF-C12W no audio

[UserXP]

Dear all,

I have this old radio clock by Sony from the early 80s, I guess. The clock display works, but is dim, the function board appears to be OK - but the radio unit shows no signs of life. It doesn't produce a single noise, crack or anything from either FM or AM band. It's like it doesn't even power up.
i opened the radio and it is full of some TRACON gray capacitors. They only have their negative strip printed, voltage and capacitace markings - no series, no temperature marking, nothing else.
My question is, do you know of this brand of capacitors and how bad are they? Also, can a failure of one or several of them cause the radio to not produce even the static noise, to be completely dead, or should I check something specific?

i checked the speaker, it passes the continuity check. Also, the Buzzer function of the alarm works, but the radio doesn't turn on then either (whereas it should). Also, the buzzer sound is faint, and when switched the Bright switch is at Low position, the digits are barely visible, the sound pitches down and then disappears. When the Bright switch is returned to High position, the sound comes back. I have another clock of this model which works well, so I can easily compare the output and notice any differencies in operation.
it is as if something is draining the voltage, depriving the radio/sound unit from power. I have attached the service manual, hopefully you will have some ideas.
Thanks in advance, guys, all the best. 🙂

[stj]

never heard of those caps but they lasted 40years
use rubycon YXF as a replacement if your not sure about specs.

[UserXP]

Thanks, I have the same idea, but YXF doesn't come in some ratings on the Farnell website I have account on. There are values such as 50V0.47uF, and such Rubycons weren't in stock, nor Panasonic, Nichicon...
I will try German Wurth Elektronik caps I ordered, they come in all ratings for this clock, and are 2000 hours at 105°C, so they ought to be better than these old Tracon caps (image included), which are likely some general purpose ones at 85°C caps. But no such data is printed their sleeve, they really look weird.

[stj]

for anything under 4.7uf i try to use polypropylene film caps now.
they are a bit bigger though.

[UserXP]

Here are some images of the boards.
I also removed these Tracon capacitors. They don't have any vent pattern on top, and the largest one (16V1000uF) may have bulged on the bottom and leaked (there is some white residue around its positive lead).

[stj]

are any of the caps bipolar (BP) ?
it's common when you have a VFD display.

[UserXP]

are any of the caps bipolar (BP) ?
it's common when you have a VFD display.

No, I don't think so. All the capacitors I removed have the negative stripe marking, so they ought to be polar electrolytic caps.

[UserXP]

Anyway, it will take a few weeks or so before I receive the order from Farnell, so hopefully the ordered capacitors will do the trick. I just hope the FM amplifier IC is not busted since none of the bands gave any sound, I'd like to believe it was just out of power due to bad caps (which I am going to test now that they have been removed from the two boards).

i am now no loner able to turn the unit on, but when I did, the display and buzzer volume were as if they were using half the supplied voltage. The VFD even flickered for a few seconds when I plugged the AC cord in, as if the power was intermittent, but then stopped. Still, it was very dim.
I also checked the transformer, it outputs 5.9V and 6.1V rails, 12V combined (it is a center tap one).

[UserXP]

Well, I was pleasantly surprised today, as the replacement capacitors arrived. I am recapping the board now. Looking forward to seeing how it will turn out. Fingers crossed.

[UserXP]

OK, people. The mystery deepens. I have replaced all the capacitors with brand new ones (WE, all are the same general purpose series, 2000 hours at 105°C) shown in the pictures. The only difference now is that the radio segment is no longer dead. The AM band has normal speaker loudness when increasing the volume knob, it just can't pick up any AM stations (as there aren't any). However, the FM band sort of works, I can tune a station and the sound is good - but very faint. I need to turn the volume knob to maximum just to be able to hear a station. So the volume knob works properly for AM, but not for FM band.
Also, the display still flickers and is faint.

I noticed with the working unit, when I unplug it from the wall, the display stays on for a second more before it fades and turns off. Also, if the radio was playing, the sound starts to fade and then disappears - all normal as the caps inside discharge.
On this problematic unit, the moment I unplug it from the wall, everything turns off immediatrely, as if there is a short or insufficient power. The caps are new, so they shouldn't cause this.

Any ideas on what to try next?
Thanks so much, as always.

[stj]

power is interesting,
start by checking the 4 diodes and parallel ceramic caps on the clock board

[UserXP]

I tried to measure the voltages first, as labeled in the service manual. The only two AC rails I managed to check are 5.9 and 6.0 volts from the center tap power transformer.
When I tried to do the same on other contacts on the board, putting the negative lead on the ground and probing with the positive lead, I get O.L. reading on the multimeter in both AC and DC mode.

[stj]

check R110 56ohm fuseable resistor to the display heaters,
and check D7,8 & 9 for reverse leakage.
i want to know why the caps are being instantly discharged.

[UserXP]

D7 shows 0.590 in normal flow and over 1 in reverse.
D8 shows 0.390 in normal flow and over 2 in reverse.
I have been unable to locate D9, a little help?

Also, there is no R110 on the function board, the one labeled 56 ohms is R108 and that is the last R1xx there. It reads -12V on its outer pad, but on the inner pad I don't get any reading. It gets warm while powered on.

[UserXP]

One other thing, when the radio clock is plugged in and no buttons are pressed, the display shows a blinking time, so that it should be set. If the brightness switch is then changed to L, the display goes very dim and the blinking pauses (it stays constantly on, but very dim). If reverted back to H, the blinking resumes. I guess the blinking is managed by the OKI chip, it must be getting insufficient power for normal operation. Just a guess.

On the working unit, the Low position of the brightness switch illuminates its display to the level at which the faulty one does on its High position (visually). The working unit display very bright symbols on High, they illuminate the surrounding edged of the tube. I can't say that the faulty unit's VFD wore out because of the other sympotms which make the radio behave is if it has insufficient power for certain functions.

[CapLeaker]

OK, people. The mystery deepens. I have replaced all the capacitors with brand new ones (WE, all are the same general purpose series, 2000 hours at 105°C) shown in the pictures. The only difference now is that the radio segment is no longer dead. The AM band has normal speaker loudness when increasing the volume knob, it just can't pick up any AM stations (as there aren't any). However, the FM band sort of works, I can tune a station and the sound is good - but very faint. I need to turn the volume knob to maximum just to be able to hear a station. So the volume knob works properly for AM, but not for FM band.
Also, the display still flickers and is faint.

I noticed with the working unit, when I unplug it from the wall, the display stays on for a second more before it fades and turns off. Also, if the radio was playing, the sound starts to fade and then disappears - all normal as the caps inside discharge.
On this problematic unit, the moment I unplug it from the wall, everything turns off immediatrely, as if there is a short or insufficient power. The caps are new, so they shouldn't cause this.

Any ideas on what to try next?
Thanks so much, as always.

With the radio stations weak, you either got the RF amp or one or more of the IF amps dead or the 455 CF is bad.

[UserXP]

With the radio stations weak, you either got the RF amp or one or more of the IF amps dead or the 455 CF is bad.

It still doesn't explain the voltage drop.
On the main board, R32 (near the Brightness switch) receives 7.56V, and it should be around 11V as it comes from the full voltage tap of the transformer, according to the manual. That is the High brightness voltage it sends to the display. When the switch is set to Low, that voltage then passes through R32 and drops to 2.56V, which is quite low for the VFD. Normally, it should be 11-12V on High and likely around 7-7.5V on Low setting.

The 7.56V rail comes from D1. It is clearly getting less than 12V. On the main board, 7.56V is the highest voltage I could measure. Only the function board receives 12V total. It looks like something on the main board is dropping the voltage by up to 4.5V, which could affect the FM function (a wild guess).

[stj]

start by spraying contact cleaner into any slide-switches.
then remove the 0.01uf(10nF) ceramic caps from the diodes and check the for leakage.
i'm looking at the "clock" board on page 7 of the manual

[UserXP]

OK, tried with the contact spray, no difference. I then checked C104 for leaking, it seems OK and no difference while it was out. The power for the VFD comes from contacts E and F on the main board. E is the one receiving voltage through the Brightness switch, and it is either 7.56V for H and 2.56 for L setting, thos voltages are entering the function board as well.

[UserXP]

I opened the working unit. The L voltage for the VFD in it is 4.5V and the H voltage is 14V. On the faulty unit, these voltages are almost half. Since the radio play at the same volume regardless of this H/L brightness position, I guess the FM amplifier needs a fixed voltage value to operate. It is frustrating that I cannot resolve the voltage drop and then see what else to look at. I noticed that the manual mentions various types of diodes, such as VD1220. I looks like a ceramic capacitor, but has a black body with two pins. It is close to the power supply input on the main board.