Samsung LE40S73

[Khron]

Long story short:

Got it for free a couple months ago. Initial symptoms: it would turn on, display "dynamic snow" in the background, and one or two (nested) windows/boxes of "static snow", for a few seconds, then the backlight cuts out, then it comes on again (same snow) for a few seconds, and so on.

PSU was full of Capxons, so a recap was the first step. Result: no change.

Got a new signal board today. Stuck it in, turned it on, got the "booting chime", and vertical rows of garbled colours. LVDS cable is fine. Now i'm starting to suspect the TCON board

With the new mobo, it DOES respond to remote key presses (menu, source, arrows), but you can't make anything out on the screen. It's like only one row of pixels is taken into account, and copied onto all the rows...

Any ideas? I can provide pics, if needed.

Later edit: I also tried starting the tv without the CI-board, and a red error window (i suspect, since i can only see vertical lines) showed up, with something white glowing/flashing.

[tom66]

Re: Samsung LE40S73

This sounds most likely to be a T-con fault. The clue is that the OSD is affected too. The T-con is often the cheapest board to replace and would be a good guess as to your problem. But good call on re-capping the power supply as these Samsung TVs have many problems with their caps going pop after a few years. Often that causes the TV to have trouble turning on, but sometimes (in rare cases) it can cause strange picture artefacts.

I fixed a Samsung TV with a T-con fault. I found a failed component on it (a voltage regulator) which caused a loss of picture apart from a few faint lines down the screen. I didn't even need to replace the whole T-con. If you post some pictures of the T-con, that would help in diagnosing your problem.

[Khron]

Re: Samsung LE40S73

You can see a picture of it HERE. The small IC on the top of the board is ok on mine (the one in this pic seems over-fluxed or melted or something)

I did probe the tabs of the three voltage regs on the right, all three were putting out around 2.5v.

There's nothing visually wrong on it, but i can take more voltage measurements if/where needed.

[tom66]

Re: Samsung LE40S73

That picture looks like the same T-con I repaired. If all regulators are putting out 2.5V, then the problem is most likely with the T-con main IC, which is not easily replaced. In other words, the T-con needs replacement.

A quick check. If you unplug the T-con and plug it back in (while the TV is running), do you get an okay image?

See if tapping the T-con with a plastic object fixes the problem (even momentarily) - could be a bad solder joint on the board.

Was the main board you used an exact replacement?

[Khron]

Re: Samsung LE40S73

Just tried it, and nope, the same vertical-line-only deal as before.

New Tcon board, then?

[tom66]

Re: Samsung LE40S73

Just tried it, and nope, the same vertical-line-only deal as before.

New Tcon board, then?

Sorry, I edited my post several times, you probably caught an earlier version... what check did you perform?

[Khron]

Re: Samsung LE40S73

First one was the connector removal/reseating - no go. Now i tried the tapping as well, and also no result.

Main chip's quite warm, so's the second-largest, and that ferrite inductor. Not 100% sure how normal the last one is though.

And the mobo replacement supposedly came out of the 32" version of this tv. I noticed there's one "extra" DPAK on it, compared to the original, rest of the layout is identical. Original board silkscreen says "Europe iDTV MP 1.2", while the replacement says "Europe iDTV CPT MP 1.0". The dates silkscreened right underneith this are about a month apart, FWIW.

[tom66]

Re: Samsung LE40S73

First one was the connector removal/reseating - no go. Now i tried the tapping as well, and also no result.

Main chip's quite warm, so's the second-largest, and that ferrite inductor. Not 100% sure how normal the last one is though.

And the mobo replacement supposedly came out of the 32" version of this tv. I noticed there's one "extra" DPAK on it, compared to the original, rest of the layout is identical. Original board silkscreen says "Europe iDTV MP 1.2", while the replacement says "Europe iDTV CPT MP 1.0". The dates silkscreened right underneith this are about a month apart, FWIW.

Most likely, that's your problem. Samsung boards need to match to the part # exactly - they probably used a different T-con on the 32" model and it's sending out the wrong signal. Try using the original board again. You can resell the new board you got - most likely it's of no real use to you. Sorry!

If you got a "somewhat" picture with the old main board, that's better than just one line repeated across the screen. Can you post a picture of what it looks like when it's faulty?

[Khron]

Re: Samsung LE40S73

I can snap a couple photos tomorrow, but i can try to describe the original board behaviour.

- turn on the tv
- backlight comes on, black-and-white "snow" is visible on the screen, all dynamic (like old tv's between tv stations)
- a "window" about 50-60% of the screen size contains "static snow" (doesn't move), and is slightly off-center, to the top-left
- within this window, there's a smaller window with a different pattern of "static snow"
- backlight cuts out after anything between 3-7 seconds or so
- backlight comes back on after 2-5 seconds, with the same image as before

I've probed the signals on the two PSU-to-mainboard connectors (one power, one inverter control) on the original one; it seems that, for some reason, the mainboard turns the backlight on and off. That particular signal goes straight into the "Sub-micom" IC (a Samsung microcontroller).

By the way, what signals is the Tcon supposed to send back to the mainboard, if any? I've got the service manual with the mainboard schematics (no psu/inverter or Tcon schematics, though).

[tom66]

Re: Samsung LE40S73

I can snap a couple photos tomorrow, but i can try to describe the original board behaviour.

- turn on the tv
- backlight comes on, black-and-white "snow" is visible on the screen, all dynamic (like old tv's between tv stations)
- a "window" about 50-60% of the screen size contains "static snow" (doesn't move), and is slightly off-center, to the top-right
- within this window, there's a smaller window with a different pattern of "static snow"
- backlight cuts out after anything between 3-7 seconds or so
- backlight comes back on after 2-5 seconds, with the same image as before

I've probed the signals on the two PSU-to-mainboard connectors (one power, one inverter control) on the original one; it seems that, for some reason, the mainboard turns the backlight on and off. That particular signal goes straight into the "Sub-micom" IC (a Samsung microcontroller).

By the way, what signals is the Tcon supposed to send back to the mainboard, if any? I've got the service manual with the mainboard schematics (no psu/inverter or Tcon schematics, though).

The T-con doesn't send any signal back to the main board - but sometimes there's a "backlight synchronisation" cable running from the PSU to T-con. I'm not entirely sure what this does, but some TVs have it and some don't. It's possible the T-con is malfunctioning and turning the backlight off.

Edit: Another possibility - the main board could be switching between modes. i.e. the first screen might be a boot logo or a channel initially with no signal and the second time the channel signal may have been detected.

[Khron]

Re: Samsung LE40S73

You can download the schematic chapter of the service manual here: link

The LVDS connector is on page 4, lower right. There does indeed seem to be a line "ending up" at a "SW_INVERTER" signal (pin 28 of the LVDS connector).

This tv has "half" of its inverter on the same pcb as the PSU: picture. That huge transformer on the lower left provides the high voltage, and there's a 5-pin connector on the top right of the PSU board, whose pin 1 is that same SW_INVERTER signal.

[tom66]

Re: Samsung LE40S73

It's possible then the faulty T-con is turning off the inverter (whether or not that is by design, I'm not sure.)

[Khron]

Re: Samsung LE40S73

So i *should* get a replacement Tcon after all...

Cheapest one i've found is this one. Really hope it'll bring this baby back to life

[tom66]

Re: Samsung LE40S73

So i *should* get a replacement Tcon after all...

Cheapest one i've found is this one. Really hope it'll bring this baby back to life

That's a pretty good price - and it should fix your problem.

[Khron]

Re: Samsung LE40S73

M'kay, ordered and paid. "Should" be here on monday (if Royal Mail moves as swiftly as usual), so expect some updates (early) next week.

Thanks for the assistance, by the way Cheers...