Car radio failure? (very strange)

[Chupo]

Hi everyone,

since a few days ago I cannot listen to any of the FM stations. Here is
what I could notice:

-MW & LW are OK

- FM sometimes works, but not for a long time (10 sec - few minutes)

- just before loosing an FM station, there is a time period of about 10
sec during which 'input level indicator' slowly arises towards the
maximum and in the same time the station fades out - afterwards, there
is only a silence

- after the station fades out: if I use a preset FM station, there is a
'full signal' indicator on the LCD, but if I try 'search', searching
starts and it searches for the infinite time (going all around through
all FM scale)

- if I am listening to a MW or a LW for a certain time period: then FM
is OK, but only for a certain time period

- longer the time period of listening to a MW or a LW station is,
longer I can use FM mode (no joke ) before it fades out as
described before

I have checked the antenna and other junctions. Does anyone know where
could the problem be? Could it be a capacitor (the fading pattern makes
me think something is slowly charging, something like an RC node). Or
maybe a PLL module? Just guessing.

ps
Sorry about my English

Thank you,

 

[Dave]

Hi everyone,

since a few days ago I cannot listen to any of the FM stations. Here is
what I could notice:

-MW & LW are OK

- FM sometimes works, but not for a long time (10 sec - few minutes)

- just before loosing an FM station, there is a time period of about 10
sec during which 'input level indicator' slowly arises towards the
maximum and in the same time the station fades out - afterwards, there
is only a silence

- after the station fades out: if I use a preset FM station, there is a
'full signal' indicator on the LCD, but if I try 'search', searching
starts and it searches for the infinite time (going all around through
all FM scale)

- if I am listening to a MW or a LW for a certain time period: then FM
is OK, but only for a certain time period

- longer the time period of listening to a MW or a LW station is,
longer I can use FM mode (no joke ) before it fades out as
described before

I have checked the antenna and other junctions. Does anyone know where
could the problem be? Could it be a capacitor (the fading pattern makes
me think something is slowly charging, something like an RC node). Or
maybe a PLL module? Just guessing.

ps
Sorry about my English

Thank you,

The signal indicator is most likely derrived from an AGC line. The fact
that it indicates full signal might mean the AGC is going to minimum
gain, when it does not need to be. There is likely to be different AGC
stages for the FM section to the AM section, as different IF gains would
be used.

 

[Dave]

There is likely to be different AGC
stages for the FM section to the AM section, as different IF gains would
be used.

Sorry, I mean different IF stages on different frequencies. The gains
might be different, but the main point is the IF and AGC will most
likely not be common.

 

[Chupo]

Sorry, I mean different IF stages on different frequencies. The gains
might be different, but the main point is the IF and AGC will most
likely not be common.

Do you think it could be repairable?

Thanks for answering me,

Best regards,

 

[Walter Harley]

Hi everyone,

since a few days ago I cannot listen to any of the FM stations. [...]

Try posting to sci.electronics.repair.

 

[Chupo]

Hi everyone,

since a few days ago I cannot listen to any of the FM stations. [...]

Try posting to sci.electronics.repair.

Yes, I have already done that and I've got some useful information
also.

Thank you,