Sony CFS-B11 Radio cassette boom box

[Nevillet]

Hi all,

I am trying to diagnose this small radio/cassette player where the audio cuts out after a few seconds - then comes back, then repeats.

I've checked the voltage and current coming from the PS board and it seems fine.

I've also powered it from a bench PS and the fault remains.

All of the electrolytics on the audio board are normal with no high ESR's or bulging tops.

Any ideas?

I've attached the service manual for the unit.

Many thanks.

[lotas]

Re: Sony CFS-B11 Radio cassette boom box

Check the headphone jack, there is a contact lock for the speakers.

[Nevillet]

Re: Sony CFS-B11 Radio cassette boom box

It doesn't seem to be the headphone jack. I've connected directly to the outputs of the TA8229K (P3+P5) and it still happens

[Nevillet]

Re: Sony CFS-B11 Radio cassette boom box

I've connected to the input pins (P11 + P12) same problem it cuts out.

[lotas]

Re: Sony CFS-B11 Radio cassette boom box

Does the sound disappear on all functions "FM", "AM", "TAPE"?

[Nevillet]

Re: Sony CFS-B11 Radio cassette boom box

yes it does on FM/AM/SW (the tape deck is non functional due to lack of belts).
I've checked the supply voltage to the tuner IC (CXA1238S) (and when working the supply is 4.2V then it disapears to 0.2V when there is no audio o/p

[stj]

Re: Sony CFS-B11 Radio cassette boom box

check the input to the amp i.c. - it could be cutting out from an internal fault.

[lotas]

Re: Sony CFS-B11 Radio cassette boom box

If there is a bolon with liquid for cleaning contacts, then you can puff to the contact groups of the switches and click them back and forth (contact may disappear in them).

[Nevillet]

Re: Sony CFS-B11 Radio cassette boom box

I think it might be the amplifier that is intermittantly shorting which drags the supply down.

[Nevillet]

Re: Sony CFS-B11 Radio cassette boom box

The switches have been disasembled and cleaned with super 10

[R_J]

Re: Sony CFS-B11 Radio cassette boom box

yes it does on FM/AM/SW (the tape deck is non functional due to lack of belts).
I've checked the supply voltage to the tuner IC (CXA1238S) (and when working the supply is 4.2V then it disapears to 0.2V when there is no audio o/p

The supply to IC301 should be 7.6 volts on pin 1, Pin 18 is a 4.8v output that is switched by the ic, This output controls the base of Q303 which supplies 4.1 volts to the tuner board, that's why that voltage is changing.

[R_J]

Re: Sony CFS-B11 Radio cassette boom box

The switches have been disasembled and cleaned with super 10

Did you have this problem before or after you disassembled the switches?