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#1 |
Badcaps Veteran
Join Date: Apr 2013
City & State: cheshire
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![]() 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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#2 |
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Join Date: Aug 2015
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Line Voltage: 230V AC, 50Hz
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![]() 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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#3 |
Badcaps Veteran
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![]() 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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#4 |
Badcaps Veteran
Join Date: Oct 2016
City & State: Bakersfield ca.
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![]() The osg displays? OSD? Are you you using remote or tv buttons? Do you get any mute message on screen?
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#5 |
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![]() 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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#6 |
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![]() Service menu : menu+info+103
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#7 |
Badcaps Veteran
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![]() had a good look in s/menu
sadly nothing in there to do with sound |
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#8 |
Badcaps Veteran
Join Date: Oct 2016
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![]() How did you verify the chip is good?
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#9 |
Badcaps Veteran
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![]() supplies to chip ok slight buzz left and right on both i/p pins
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#10 |
Badcaps Veteran
Join Date: Oct 2016
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![]() So you need 4-5vdc on pin 6 to make active. 0 to 2.5vdc to mute and standby.
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#11 |
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![]() 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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#12 |
Badcaps Veteran
Join Date: Oct 2016
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![]() So what voltage do you have on pin6?
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#13 | |
Badcaps Veteran
Join Date: Aug 2015
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![]() Quote:
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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#14 |
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![]() 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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#15 |
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#16 |
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![]() 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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#17 |
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![]() 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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