THOMSON 32lb120s4 no sound

**jimbofz** · 11-11-2021, 07:17 AM

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?

**dick_barton** · 11-14-2021, 11:05 AM

The THOMSON Chassis LCD12B 20LB120S4 may give you some insight into the audio section
https://www.electronica-pt.com/esque...ileinfo/11059/

**jimbofz** · 11-15-2021, 01:54 PM

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

**dskall** · 11-16-2021, 02:47 PM

The osg displays? OSD? Are you you using remote or tv buttons? Do you get any mute message on screen?

**jimbofz** · 11-18-2021, 04:11 AM

yes mute osg as normal
vol graphic as normal but not a peep of sound ,
headphone socket also eliminated ,
no sound with headphones

**lotas** · 11-18-2021, 04:23 AM

Service menu : menu+info+103

**jimbofz** · 11-18-2021, 12:56 PM

had a good look in s/menu
sadly nothing in there to do with sound

**dskall** · 11-18-2021, 05:53 PM

How did you verify the chip is good?

**jimbofz** · 11-19-2021, 02:14 PM

supplies to chip ok slight buzz left and right on both i/p pins

**dskall** · 11-19-2021, 11:05 PM

So you need 4-5vdc on pin 6 to make active. 0 to 2.5vdc to mute and standby.

**jimbofz** · 11-20-2021, 06:27 AM

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

**dskall** · 11-20-2021, 11:40 AM

So what voltage do you have on pin6?

**dick_barton** · 11-20-2021, 05:17 PM

Quote:

Originally Posted by jimbofz

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

**jimbofz** · 11-21-2021, 05:35 AM

so that explaines where the 5v comes from .
its not clear from the cct .
i now understand its from within the ic

**jimbofz** · 11-21-2021, 05:37 AM

Quote:

Originally Posted by dskall

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

**dick_barton** · 11-21-2021, 05:52 AM

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.

**jimbofz** · 11-21-2021, 08:28 AM

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

11-14-2021, 11:05 AM	#2
dick_barton Badcaps Veteran Join Date: Aug 2015 City & State: Cardiff My Country: Wales Line Voltage: 230V AC, 50Hz I'm a: Hobbyist Tech Posts: 6,544	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/ __________________ Willing to help but I'm no expert.

11-15-2021, 01:54 PM	#3
jimbofz Badcaps Veteran Join Date: Apr 2013 City & State: cheshire My Country: uk I'm a: Knowledge Seeker Posts: 390	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

11-16-2021, 02:47 PM	#4
dskall Badcaps Veteran Join Date: Oct 2016 City & State: Bakersfield ca. My Country: usa Line Voltage: 120VAC 60Hz I'm a: Knowledge Seeker Posts: 2,802	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? __________________ I assume no responsibility for any stupid suggestions I might post.

11-18-2021, 04:11 AM	#5
jimbofz Badcaps Veteran Join Date: Apr 2013 City & State: cheshire My Country: uk I'm a: Knowledge Seeker Posts: 390	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

11-18-2021, 04:23 AM	#6
lotas Badcaps Veteran Join Date: Jan 2016 City & State: Sochi My Country: russia I'm a: Knowledge Seeker Posts: 852	Re: THOMSON 32lb120s4 no sound Service menu : menu+info+103

11-18-2021, 12:56 PM	#7
jimbofz Badcaps Veteran Join Date: Apr 2013 City & State: cheshire My Country: uk I'm a: Knowledge Seeker Posts: 390	Re: THOMSON 32lb120s4 no sound had a good look in s/menu sadly nothing in there to do with sound

11-18-2021, 05:53 PM	#8
dskall Badcaps Veteran Join Date: Oct 2016 City & State: Bakersfield ca. My Country: usa Line Voltage: 120VAC 60Hz I'm a: Knowledge Seeker Posts: 2,802	Re: THOMSON 32lb120s4 no sound How did you verify the chip is good?

11-19-2021, 02:14 PM	#9
jimbofz Badcaps Veteran Join Date: Apr 2013 City & State: cheshire My Country: uk I'm a: Knowledge Seeker Posts: 390	Re: THOMSON 32lb120s4 no sound supplies to chip ok slight buzz left and right on both i/p pins

11-19-2021, 11:05 PM	#10
dskall Badcaps Veteran Join Date: Oct 2016 City & State: Bakersfield ca. My Country: usa Line Voltage: 120VAC 60Hz I'm a: Knowledge Seeker Posts: 2,802	Re: THOMSON 32lb120s4 no sound So you need 4-5vdc on pin 6 to make active. 0 to 2.5vdc to mute and standby.

11-20-2021, 11:40 AM	#12
dskall Badcaps Veteran Join Date: Oct 2016 City & State: Bakersfield ca. My Country: usa Line Voltage: 120VAC 60Hz I'm a: Knowledge Seeker Posts: 2,802	Re: THOMSON 32lb120s4 no sound So what voltage do you have on pin6?

11-21-2021, 05:35 AM	#14
jimbofz Badcaps Veteran Join Date: Apr 2013 City & State: cheshire My Country: uk I'm a: Knowledge Seeker Posts: 390	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

11-21-2021, 05:52 AM	#16
dick_barton Badcaps Veteran Join Date: Aug 2015 City & State: Cardiff My Country: Wales Line Voltage: 230V AC, 50Hz I'm a: Hobbyist Tech Posts: 6,544	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..

11-21-2021, 08:28 AM	#17
jimbofz Badcaps Veteran Join Date: Apr 2013 City & State: cheshire My Country: uk I'm a: Knowledge Seeker Posts: 390	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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