Skoda car radio - No output sound.

[AlenZGB]

Hello

im trying to fix skoda octavia 2 car radio, i dont have sound on output pins.
Firstly there was some problem with antena signal. but output sound was ok.
now it try with CD and it wont play sounds, time for song is turning but no output sound.
is there and way to check the output voltages or something like that ?

Im also suspecting on something but not sure for 100%
This item should be fixed on that aluminum plate behind it i think for cooling,
maybe that die due overheating, even if i dont smell anything burned but still.

Any suggestion ?

Regards,
Alen

 

[Gryd3]

Can you please verify the current problem is only with CDs?

Firstly there was some problem with antena signal. but output sound was ok.

 

[AlenZGB]

I think the problem with no output sound dont have anything to do with input media(radio FM or CD)
i just use CD couse i know i will have to get some output sound, couse im not sure if i will have any signal from antena.

I hope ill look into it tomorrow and take few pictures, but i want to measure something if i can.

 

[shrtrnd]

My initial thought is that you said you thought you had a problem with the reception signal.
That may not have been a reception problem, it may have been an amplifier output semiconductor going bad.
If you want something to check, (with the power disconnected), measure the resistance across the amplifier output transistors,
and see if you have any shorts or opens within them.

 

[AlenZGB]

when following antena lead i can see some weird small coil 3x4 mm size, aprox. that look not so good.
but ill took pictures tomorrow. But theory with amplifier transistor could also be true.
do i need to desolder that transistor or that can be measured on board ?

 

[shrtrnd]

We don't know where to start yet. Your small coil is probably intended to cut-down on RF interference on the antenna input line.
It's highly unlikely that that is the problem (unless you can see physical damage of some type).
Just reading across the coil for a (very) small resistance will tell you if it's open-circuit or not.
I'd just measure the transistor in-place right now. It's connected into the circuit and would read the resistance of other components in the circuit
but you sounded like you were anxious to take a reading or two to look for obvious failures, so I thought a quick in-circuit check would be a good
place to start. Unusual resistances across the transistors would make them subject to closer scrutiny. What you're looking for in this check is a
direct shorted transistor (no resistance between the pins.)
Your symptoms indicate a failed component or two inside the chassis, not an antenna problem.
Other high-failure possibilities would be the large electrolytic capacitors, like the one in your picture.
They're made of a wet-electrolyte that dries (faster in high-heat exposure), and fail.
My guess is that if it's not the caps, your power semiconductors are the place to look.

 

[AlenZGB]

i try that big cap seems ok.
try that 3 pin transistor on the side shows no short circuit on it but also no ohm at all whatever i connect probes.
here few more pictures maybe you can suggest me something else to check