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Old 11-11-2021, 07:17 AM   #1
jimbofz
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Default THOMSON 32lb120s4 no sound

Hi can anyone help please with cct diagram ,ive looked for hours
this tv has no sound but the o/p stage is fine ,so suspect main board ,poss corrupt f/w?
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Old 11-14-2021, 11:05 AM   #2
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Default Re: THOMSON 32lb120s4 no sound

The THOMSON Chassis LCD12B 20LB120S4 may give you some insight into the audio section
https://www.electronica-pt.com/esque...ileinfo/11059/
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Old 11-15-2021, 01:54 PM   #3
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Default Re: THOMSON 32lb120s4 no sound

thanks for taking time to help .sadly this version you posted is different to mine the version i have has a TDA7490L for its sound o/p stage ,pin 6 of which is mute/on off .
now when you press mute the osg shows on screen.
the transistor q1 is used to switch mute on off
there are 2 supplies -16v and +16v both present
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Old 11-16-2021, 02:47 PM   #4
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Default Re: THOMSON 32lb120s4 no sound

The osg displays? OSD? Are you you using remote or tv buttons? Do you get any mute message on screen?
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Old 11-18-2021, 04:11 AM   #5
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Default Re: THOMSON 32lb120s4 no sound

yes mute osg as normal
vol graphic as normal but not a peep of sound ,
headphone socket also eliminated ,
no sound with headphones
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Old 11-18-2021, 04:23 AM   #6
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Default Re: THOMSON 32lb120s4 no sound

Service menu : menu+info+103
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Old 11-18-2021, 12:56 PM   #7
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Default Re: THOMSON 32lb120s4 no sound

had a good look in s/menu
sadly nothing in there to do with sound
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Old 11-18-2021, 05:53 PM   #8
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Default Re: THOMSON 32lb120s4 no sound

How did you verify the chip is good?
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Old 11-19-2021, 02:14 PM   #9
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Default Re: THOMSON 32lb120s4 no sound

supplies to chip ok slight buzz left and right on both i/p pins
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Old 11-19-2021, 11:05 PM   #10
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Default Re: THOMSON 32lb120s4 no sound

So you need 4-5vdc on pin 6 to make active. 0 to 2.5vdc to mute and standby.
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Old 11-20-2021, 06:27 AM   #11
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Default Re: THOMSON 32lb120s4 no sound

finally found cct .page 17 is audio o/p ,
strange theres no 5v supply shown on cct
it seems that the chip works without ?
please have a look
the cct is same even though the model number is 125 not 120
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Old 11-20-2021, 11:40 AM   #12
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Default Re: THOMSON 32lb120s4 no sound

So what voltage do you have on pin6?
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Old 11-20-2021, 05:17 PM   #13
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Default Re: THOMSON 32lb120s4 no sound

Quote:
Originally Posted by jimbofz View Post
finally found cct .page 17 is audio o/p ,
strange theres no 5v supply shown on cct
it seems that the chip works without ?
please have a look
the cct is same even though the model number is 125 not 120
The +5V and -5V are internally generated by the TDA7490L and available on pin 12 (+5V) and pin 16 (-5V).
The +5V (+VA5) then goes off to supply Q1 which controls the ON/OFF and Mute function.



https://www.st.com/resource/en/datasheet/cd00002355.pdf

Last edited by dick_barton; 11-20-2021 at 05:23 PM..
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Old 11-21-2021, 05:35 AM   #14
jimbofz
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Default Re: THOMSON 32lb120s4 no sound

so that explaines where the 5v comes from .
its not clear from the cct .
i now understand its from within the ic
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Old 11-21-2021, 05:37 AM   #15
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Default Re: THOMSON 32lb120s4 no sound

Quote:
Originally Posted by dskall View Post
So you need 4-5vdc on pin 6 to make active. 0 to 2.5vdc to mute and standby.
the voltage is .05v ,so ill try to get replacement ic thanks
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Old 11-21-2021, 05:52 AM   #16
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Default Re: THOMSON 32lb120s4 no sound

You may have a faulty Q1 or the +5V from the TDA7490L may be missing or either the ON/OFF or MUTE signal may be stuck at +5V.

Last edited by dick_barton; 11-21-2021 at 05:55 AM..
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Old 11-21-2021, 08:28 AM   #17
jimbofz
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Default Re: THOMSON 32lb120s4 no sound

i will check as soon as i get my hands on the tv .the owner has taken it back and for the time being is using external audio out phonos from his sat box to his stereo system ,as he only uses scart on his tv ,uses the sound vol control on sat box. i will post update asap
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