How I Repaired SONY TV Power Supply Model: T370XW02 Made In Taiwan
This TV was made in Taiwan and I received it in my lab with panel problem but after one or two time on/off, the TV can’t be turned On again.
Shorted wires of lvds cable made this problem for this panel
Burned pixels on screen due to bad lvds cable
The TV already 15 years old and eligible to have many problems like bad caps and cold joints and so forth. Since the TV can’t be turned On so the main suspect was power supply.
The power supply was made by SUNKEN co. in Indonesia and assembled in Sony co. in Taiwan.
The first component after AC terminal input was VDR ( volt dependent resistor ). If the unwanted voltage at the entrance of power supply are going up more than limitation of VDR, the resistance of VDR will gets higher to protect the entire circuit against higher voltage. Usually VDRs are getting short most of the time but in this case, VDR was not shorted. But what if this VDR was open? Actually there was no difference between an open VDR and a good one because our normal multimeter can’t test it. If you want to test for short circuit, you can use analogue mutlimeter set to 10 kOhm range and it should not have any reading. I decided to replace VDR with a new one, but after replacing it there was no progress at all.
On the way down to the bridge rectifier there was two toroid coils that were intact, these toroid coils protect the power supply against unwanted frequencies of AC voltages. The next components were two MKT CAPs that one of them showed very high ESR about 65 ohm but comparing to same kind cap and with same value I convinced that the MKT CAP was also good and the ESR is in the tolerance range. The next component in this direction was a black NTC and this is another protective component in AC entrance line to the TV.
The NTC is based on Negative Temperature Coefficient and this means if the temperature of component goes up the resistance value comes down. This is how I perform the test on the NTC.
I hooked the pins of NTC to the probe of analog multimeter and selector must be on 1 ohm and the multimeter showed 5 ohms. With the help of a hot soldering iron and placing it close to the NTC, a good NTC will react to the heat and the resistance started to decrease. But in my case the NTC did not react to the heat. This means the NTC is open circuited. By replacing the NTC with the same rating, 220 volts are reaching to AC pins of Bridge Rectifier (BR) but very low DC volts on output of BR (about 6 volts) so I can assumed that BR was not good.
So I replaced the BR with a new Bridge rectifier same kind but with different part number. Now I have proper voltage DC out of BR.
By measuring the voltages on the pins of the big filter capacitor, I got about 200 volt DC which was low. It supposed to have about 300VDC. The value of cap was 270 microfarad but ESR meter read this cap just 240 microfarad and ESR of 2 ohm. 2 Ohms ESR means the capacitor is bad. I replaced this capacitor and now have about 300 volt DC across the two pins of the big filter capacitor.
I forgot to explain also that one relay before NTC was tested good. I replaced a resistor with printed value 4.7 ohm ceramic ½ watt that was open and it acted as a fuse in the board .
Now I have 3.3 volts in output terminal of power supply (psu) to feed CPU and start the TV.
Bad TV parts
And yes I have to find a way or make a way to solve the panel problem of this TV as well from now.
This article was prepared for you by Mr Beh from Iran
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Note: You can check his previous article on How 10“ Wired Video Intercom System Doorbell With Camera And Monitor Plus Memory Door Security System TABA Is Repaired model: TVD-1035
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21 Comments
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Waleed Rishmawi
April 29, 2023 at 4:58 pm
I hope you will be able to fix the panel issues because it would be a waste of time working on this power supply. any way, thanks for sharing and have a blessed day
beh
April 29, 2023 at 7:29 pm
Yes Waleed the only way that is left is to replace the panel with a good one
Hollis LuQuette
April 29, 2023 at 11:33 pm
If you can find the clock inputs to the LCD panel , you can delete those inputs and those bad pixels will not show up ... I could leave a link to a video to show how but I don't know if that is allowed in comments , This is only my 2nd time commenting here....
beh
April 30, 2023 at 3:43 pm
Hi Hollis
I want to welcome you to our weblog. Also i want to ask our Dear Admin and instructor Mr Jestine Yong to give you this permission to send us this link since this problem is common for all must be useful.
Beh
May 1, 2023 at 1:38 am
Hollis
Since Mr Yong pubilshed my comment he is agree you send the link to us
Thanks
Beh
Albert van Bemmelen
April 29, 2023 at 5:09 pm
Very nice explanation of testing the various components on the AC in- and DC output of the TV power circuit! I suppose that fixing this defect old display panel is no longer an option. Replacing it with another identical screen if still available will probably be the best way to fix it.
Parasuraman S
April 29, 2023 at 7:05 pm
Excellent explanation! Thanks for sharing!
beh
April 29, 2023 at 10:20 pm
Parasuraman
Thank you so much of your kind words
Behzad
Beh
May 1, 2023 at 1:28 am
Hi Zed
Same as my country the technician just looking to find same boards to repair the Tv mostly from junk Tvs and or broken panel Tv s those board also does not long last many and set return again to the shop
and thanks for your comment
beh
April 29, 2023 at 7:32 pm
Albert i am looking for a good panel for this TV to replace it very soon .
Arun Kumar
April 30, 2023 at 1:49 am
Good job.
Don't give up.
You will do it.
Update once completed.
beh
April 30, 2023 at 8:57 am
Arun
Thanks .I ll do so .soon.
Beh
Zed Pato
April 30, 2023 at 10:07 am
Nice job beh that is patience in technician board level repair some technician always look for same board to replace but you show you us patience gives rewards in repair and knowledge in how to test a component
ariel
April 30, 2023 at 2:47 pm
your effort work well mate.thank for sharing
Beh
May 1, 2023 at 9:41 am
Ariel
Thanks for your comment.
Beh
April 30, 2023 at 7:55 pm
Hi Zed
Same as my country the technician just looking to find same boards to repair the Tv mostly from junk Tvs and or broken panel Tv s those board also does not long last many and set return again to the shop
and thanks for your comment
Humphrey
May 2, 2023 at 2:41 am
Thank you for the article my friend Beh, glad to see you back at on this blog.
Regards Humphrey
Beh
May 2, 2023 at 6:56 pm
Hi Humphery
I never left the weblog if i am in silenec this does not mean i am not presnt here i just study the aritcles of
Other members and learning from you all and thanks for your comment.
Beh
Yogesh Panchal
May 18, 2023 at 12:17 am
Good Fix! Beh.
Beh
May 19, 2023 at 2:28 pm
Yoghesh
Thank you so much
Beh
francis machika
December 21, 2024 at 1:37 pm
good lecturing.