Samsung LE40A676 dark picture

[budm]

Re: Samsung LE40A676 dark picture

Does this TV has DEMO mode (it shows pre-loaded pictures like screen))? That is how I found out the backlikghts are OK because the pictures look perfect in DEMO mode. I did not try to download the user manual for you model to find out if it has that mode or not due to 26MB download.

[PowerAmpFreak]

Re: Samsung LE40A676 dark picture

Measured the PWM_DIM which I assume is the backlight brightness control signal.
It changes when backlight is adjusted in user menu. From 0.1V to 0.35V maximum.
So I guess the mainboard is bad.
Will check what happens if pull this pin to +5V through 1k

[tom66]

Re: Samsung LE40A676 dark picture

Yeah, maybe bad opamp or output on main board, or IP b/d loading it down too much.

[PowerAmpFreak]

Re: Samsung LE40A676 dark picture

When pulling up the PWM_DIM to +5V through 1k, the potential rises to +3,36V and screen perfectly bright.
What is strange - in service menu, I cannot select "Advanced" submenu. It does not react.

[PowerAmpFreak]

Re: Samsung LE40A676 dark picture

The owner of this TV just want it to work, so if everything seems to work, could the 1k resistor be permanent mounted?
(without the risk of over driving the backlight)

[tom66]

Re: Samsung LE40A676 dark picture

Yeah, it should be fine. You won't be able to adjust the backlight, and the display may flicker when changing channels or sources. The backlight adjust is only used in user menu, and in the godawful dynamic mode. Dynamic mode seems to adjust the backlight about 100ms after the picture dims on these models, making it uncomfortable to look at. Not sure why it is so out of sync, but I've never liked it.

[vinceroger69]

Re: Samsung LE40A676 dark picture

When pulling up the PWM_DIM to +5V through 1k, the potential rises to +3,36V and screen perfectly bright.
What is strange - in service menu, I cannot select "Advanced" submenu. It does not react.

off another site try at your own risk !!!!
When the TV is off, hit INFO MENU MUTE POWER keys in this order. The TV turns on and you see a large menu structure. If you do not see the menu, try the same procedure with MUTE, 1, 8, 2, POWER instead. Usage: Up&Down arrows make selections while Right&Left arrows makes changes. You needed to backup previous value before changing any option. Some options cannot be reverted once changed. The service menu has a protected 'advanced' submenu. Press the 0 button four times on advanced to enter the hidden menu. Before touching any setting, please note the original value

[PowerAmpFreak]

Re: Samsung LE40A676 dark picture

Great info. Now I can open the advanced tab!
BUT - I notice that the TV won't tune any analogue channels ...
Found the factory reset and made it, no help for channel tuning

[tom66]

Re: Samsung LE40A676 dark picture

Umm, didn't they switch off analogue broadcasting in most of Europe after 2012? Try digital.

[PowerAmpFreak]

Re: Samsung LE40A676 dark picture

I've learned from experience, when a Samsung mainboard is "weird", sometimes the tuner doesn't work properly. Therefore I have an RF modulator set to CH45 and confirms it can recieve this signal.
This one doesn't and can't even show (don't know what's called in english, the noise when no channel is tuned)
Of course it's set to analogue aswell.

[tom66]

Re: Samsung LE40A676 dark picture

Does the digital tuner work or not?
In service menu make sure tuner type is set correctly for example if it has SAMSUNG tuner set to SAMSUNG.

[budm]

Re: Samsung LE40A676 dark picture

So, are you able to do FACTORY reset from the service mode? Does the screen show bright pictures now? The analog signals are gone long time ago.

[PowerAmpFreak]

Re: Samsung LE40A676 dark picture

I'm using an RF modulator tuned to CH45 to verify tuner is OK.
This doesn't even show snow. HDMI's and everything else seems to work properly.
Please see the attached pictures from service menu.

There is a feature "EEPROM RESET" , what does it do ?
Please check if the TUNER submenu looks correct (pic4)

[tom66]

Re: Samsung LE40A676 dark picture

Check DEMOD TYPE matches what is written on the metal tuner case.
Check PLL TYPE (chipset) can be found on the circuit board, should be near the tuner box.
Also, check +33V for tuner. Can be found on one of the tuner pins.
And, again, does digital work or not?

[PowerAmpFreak]

Re: Samsung LE40A676 dark picture

Haven't had the chance of checking the digital tuner yet. Back tomorrow. Thanks!

[Clydeuk]

Re: Samsung LE40A676 dark picture

We used to use a service remote to enter the advanced options. I'm looking into emulating one or doctoring an old remote if possible. There may be a combination of keys you can use on a universal remote to get this extra function, depending on what universal you can try. I believe the panel type etc is set in the advanced options, you may find it's set incorrectly or something else in there is. I don't have time during the week to look further.

[PowerAmpFreak]

Re: Samsung LE40A676 dark picture

With help of vince above (pressing a few zeros) I was able to open advanced tab.

[Clydeuk]

Re: Samsung LE40A676 dark picture

Excellent info. I need this procedure myself, thanks

[budm]

Re: Samsung LE40A676 dark picture

The question is that, do you get good brightness now after activating the FACTORY reset?

[PowerAmpFreak]

Re: Samsung LE40A676 dark picture

Factory reset did not change the dark screen unfortunately.
It does not tune in either analogue or digital channels.
Owner will keep this TV only for HDMI use and with a small modification to increase the screen brightness (1k4 resistor between +5V and PWM_DIM)

So, finally. This set has a faulty mainboard and hardly worth replacing.
My experience is that Samsung's has really sensitive mainboards.