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Equipment Repairs => LCD TV forum => Topic started by: t1412 on January 08, 2019,14:04:29

Title: tx-42A400b
Post by: t1412 on January 08, 2019,14:04:29

hi fella's anyone got service manual for this tv panasonic tx-42A400B, you turn the tv on screen flashes up for second the red standby light flashes slowly backlight working  tester with backlight tester at the connections on the psu, psu voltages 5.1v no 3.3 thanks for your time

shaun

Title: Re: tx-42A400b
Post by: jordan on January 08, 2019,15:23:43

https://www.electronica-pt.com/esquema/tv/panasonic-esquemas-tv/panasonic-tx-42a400b-chassis-km25e-32804/

Title: Re: tx-42A400b
Post by: downunder on January 09, 2019,03:23:17

Hi Shaun,

I take it the red LED is flashing code 1 which is a backlight fault. The LED driver board is usually bullet-proof, unless it's had external interference like fluid spilt on it.

While I'm thankful for the LED tester, it doesn't always reveal a faulty LED string because it a low current device and doesn't duplicate the operating condition of the LEDs (which are usually wound up to maximum brightness). Do you mean the 3.3V is missing?

Some punctuation marks would be helpful.           Bruce

Title: Re: tx-42A400b
Post by: Turnip on January 09, 2019,12:58:21

Hi Shaun,

Agree with Bruce, had a similar set where code 1 was the biz, though the edge lights tested OK, in and out of the set.
New led strip from China sorted the code issue, though still can't sort any duff Leds on the old strip - Chris.

Title: Re: tx-42A400b
Post by: t1412 on January 09, 2019,13:04:03

hi bruse thanks for the info, if the backlight as gone i should be able to see an image, which i don't, so a bit confused,   

Title: Re: tx-42A400b
Post by: downunder on January 10, 2019,00:52:49

Well no, Shaun. Once an error has been detected and the CPU generates an error code, Panasonic TVs are locked down thereafter. 1 second to black after switch on is usually a backlight fault in most LED TVs.

So, you have standby-5V present at all times. What about Power-On and BL-On voltages ? You may in fact have a faulty A-board (Main).

Title: Re: tx-42A400b
Post by: t1412 on January 12, 2019,01:35:37

change the mainboard still the same i'll test the led thanks

Title: Re: tx-42A400b
Post by: Turnip on January 12, 2019,10:44:37

Hi Shaun,

Leds don't always show as faulty. Had one with the 'one flash' where all four strings on the long side strip checked OK, even out of the set with 300 m/a up them (Strip got rather hot though, off the heatsink)

Answer was a new strip £40+ locally or £18 freepost from China if you don't mind the fortnight wait - Chris.

Title: Re: tx-42A400b
Post by: sinclairtv on January 13, 2019,11:31:14

So has this set got sidelight or back lights.