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Old 10th Jul 2013, 11:01 am   #1
chompy1
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Default Philips portable (X12T 740/94)

Hi All,
The set has no audio. All the transistors in the audio output stage have tested out ok.

Does the TBA240 play any part in driving the audio stages?

Thanks, Paul
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Old 10th Jul 2013, 12:23 pm   #2
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Default Re: Philips portable (X12T 740/94)

If there is headphone socket try this first, it might respond to some cleaning other than that check the voltage supply to the output stage, which I think comes from the line output stage, and try the figure or buzz test on the the wiper of the volume control or on the audio input circuit.
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Old 10th Jul 2013, 12:53 pm   #3
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Default Re: Philips portable (X12T 740/94)

thanks Simon, I'll give that a go this afternoon.

Cheers, Paul
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Old 10th Jul 2013, 1:02 pm   #4
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Default Re: Philips portable (X12T 740/94)

I'm pretty sure the TBA240 is only the sync separator and line/field oscillator. A sync driven mute circuit wasn't used until much later.
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Old 11th Jul 2013, 10:02 am   #5
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Default Re: Philips portable (X12T 740/94)

Hi Paul.

I've had a look at the circuit which is in Radio and Television Servicing 1972-1973. Your set has the Philips T4 chassis fitted.
The 10.7V supply (designated +3) goes to the audio output stage, TS 406 collector. This same supply also goes to the intercarrier ic TAA750 pin 5.
The 10.7V supply originates from power supply regulator. It might be as well to check fusible resistor R657 (3.3 Ohm).
If required, I could scan and send you the circuit details.

Regards
Symon.
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Old 11th Jul 2013, 12:58 pm   #6
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Default Re: Philips portable (X12T 740/94)

Just for information, the /94 will not be PAL I (6Mhz sound) so you won't get sound unless it's been modified at some stage. UK models are /05 or /25. No idea what country /94 was for as I no longer have my Philips notes but high numbers like that tended to be Far Eastern. If it's working on the wrong sound frequency, some sets muted so you also won't get any 'mush'. I don't think this used a ceramic filter in the sound so you may be able to adjust the sound I.F coil. If you can get a Philips circuit, they usually gave the information on different value capacitors for different sound I.F. Sometimes you could get away with just retuning, other time you had to change capacitors as well.


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Old 11th Jul 2013, 9:51 pm   #7
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Default Re: Philips portable (X12T 740/94)

I would be very interested to hear what letters are in front of the serial number. Usually, those sets were built in Monza with the relevant letter combination being PM. If the set was intended for the far east, it might have been made in another factory.
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Old 12th Jul 2013, 12:17 am   #8
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Default Re: Philips portable (X12T 740/94)

Hi Chaps,
I checked R657 as Symon suggested and it was O/C. I fitted a replacement and the audio has now been restored.

The serial number is SV-221451.

Thanks All, Paul
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Old 12th Jul 2013, 7:35 am   #9
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Default Re: Philips portable (X12T 740/94)

Quote:
Originally Posted by chompy1 View Post
Hi Chaps,
I checked R657 as Symon suggested and it was O/C. I fitted a replacement and the audio has now been restored.

The serial number is SV-221451.

Thanks All, Paul
Hello,

Probably made in Philips' Singapore factory. The later versions of the X12T740 that were sold in the UK were. They usually had a label on the case to that effect.

Regards,

Dazzlevision
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Old 12th Jul 2013, 9:43 am   #10
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Default Re: Philips portable (X12T 740/94)

I'll see if I can find out where /94 was originally intended for. Many sets were brought over from abroad during the 70's. Some were modified easily.

Yes agree that 'SV' means that it was made in Singapore.

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Old 12th Jul 2013, 11:04 am   #11
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Default Re: Philips portable (X12T 740/94)

did they have to change any capacitors in the tuner circuitry?

Cheers, Paul
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Old 13th Jul 2013, 8:38 pm   #12
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Default Re: Philips portable (X12T 740/94)

I've been playing around with the set this afternoon, and I don't think it's ever been modified, because it wont tune in to the freeview box properly. Also, it doesn't have the normal snowy background.

Does anyone have the details of how to carry out the modification?

Thanks, Paul
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Old 13th Jul 2013, 10:38 pm   #13
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Default Re: Philips portable (X12T 740/94)

Correction:- the set doesn't have the usual snowy picture when not tuned in at all.

Is the modification purely just for audio or is it for audio and picture?

Cheers, Paul
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Old 13th Jul 2013, 10:54 pm   #14
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Default Re: Philips portable (X12T 740/94)

The only components changed if necessary was a capacitor that tuned the sound quad coil. It was then just a question of carefully tuning the quad coil for max sound, minimum buzz. On some occasions, the tuner would need changing but most continental sets tune VHF/UHF so it wasn't normally necessary.

Theoretically, some vision IF adjustments would have been necessary but in practice, this was never required.


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Old 14th Jul 2013, 12:51 pm   #15
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Default Re: Philips portable (X12T 740/94)

Thanks Rich.
It's looking like I may have to shelve this one until I can get a diagram for it.

Cheers, Paul
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