Samsung LE32R41B foggy picture

[tom66]

Re: Samsung LE32R41B foggy picture

Love the idea of using multiple batteries and SMPS to get the display going.

I don't think that line is going away although perhaps some tab bond fiddling may fix it, if you're brave.

Perhaps the output diode of the boost is bad? Otherwise, I would expect, say, 4.3~4.7V out, instead of 5.1V (exactly equal to input.)

VCOM should also be checked. I think it's supposed to be half AVDD. VCOM is very important: the panel will probably work without it, but it will cause damage to the LCD panel through image retention due to liquid crystal DC bias.

[Th3_uN1Qu3]

Re: Samsung LE32R41B foggy picture

I have already fiddled with all tab bonds yesterday, with no change about that line. I don't want to break this panel further, besides, since the line is horizontal, transparent and dependent on picture content, it doesn't bother me that much.

I'll be keeping this TV, at least for a while. I've got too much work into it already and i won't be able to get a good price on it with that line, so i'll hold onto it. It was about time i got a proper screen to watch. I also like that it has some proper speakers inside - it's got 2 little speakers that output thru the front, and 2 small woofers, complete with bass-reflex enclosures, which fire downwards. This TV was made in 2005 - the "slim" craze wasn't that ridiculous back then.

Btw, i just pulled the shield off the Tcon that currently resides in the TV. It's got the same bridge over the VCC and WP pins of the EEPROM, and it is VERY clean. It seems factory. So it's likely that the original Tcon wasn't tampered with, either. Looks like i got 2 bad Tcons, with likely the same failure.

Oh, and with all my external powering, i think i've blown a fuse, as AVDD is now 0 when not powered externally. Well, i need to fiddle with that circuit anyway, and i've got spares, so that's not a problem.

[Th3_uN1Qu3]

Re: Samsung LE32R41B foggy picture

Okay, i think i've gotten to the bottom of this. I've tested the original Tcon and it's definitely bad, it cycles thru what seems like corrupted test patterns and doesn't even drive the panel properly, there's still ghosting. Its power supply behaves the same, i still had to power the panel externally.

What i thought was a fuse (the part which i've blown on the good Tcon) is actually some sort of shunt. On the bad Tcon, it was dropping quite a bit of voltage under a 10 ohm load even after the boost converter shut down, a rough calculation shows it's ~0.5 ohms. A bit high for a shunt, but ahh well.

Installing a 20 mohm shunt instead didn't stop the power supply from falling flat on its face. When load testing the AVDD supply with the 10 ohm resistor, it held on a bit longer (just enough to register a couple readings on my DMM), and this time it shut down due to undervoltage not overcurrent, as the voltage dropped down to 11v before the boost converter shut down. Previously, it would shut down almost instantly. A 20 ohm load is fine in both cases. The VGH supply is fine with a 100 ohm load. VGL also falls flat on its face with a 10 ohm load, but the panel only draws a couple dozen mA from that, so i suspect that's normal behavior.

Thing is, if either of the 3 voltages encounters a condition, all 3 are shut down. The panel itself is what's causing this, as i noticed something. If i plug in the AVDD supply with the TV turned OFF, the hacked laptop power brick i'm using to power it goes into protection mode, and that thing is capable of 5 amps!!! I see 2.4A pulses as the power brick tries to recover. After i turn on the TV, it goes out of current limiting, and settles down to ~0.2A.

On the other hand, with the TV still turned off, if i power up VGL and VGH first, and then AVDD, it only draws 0.14A and stays at that until i turn the TV on. The highest spike before a picture shows is 0.23A, and the panel draws 0.24A from AVDD on full white, so that isn't a problem, and well within the capabilities of the power supply on the Tcon.

If i plug AVDD in after the TV is turned on and the panel is receiving a signal, there is no problem. If there was, i would have noticed it until now, as before i discovered that the other two were missing as well, i was running the panel with AVDD only.

What i'm going to do tomorrow is identify the protection/shutdown pins of the controllers on the Tcon, and attempt to restart the power supply on the Tcon and see if it stays on after the panel has started receiving a signal. If it does, i think i have a simple solution for this issue. Two, in fact. So yes... it is a bad panel after all, but there's hope.

Oh btw, i'm glad i put limiting resistors in series with the wires i soldered for powering the display externally, as i made a mistake and was fairly sure i blew the panel... but i didn't. I was measuring the current draw on each of the 3 supplies with the TV turned off, and instead of touching the VGH wire with my amp meter probe coming from the two SLA batteries in series, i touched VGL... The resistor briefly smoked and i immediately pulled the probe away.

The panel still lives to tell the tale. Phew, that was close. If that resistor wasn't there, i'm pretty sure i would have fried this screen for good.

[tom66]

Re: Samsung LE32R41B foggy picture

Perhaps some heavy soft-start or large capacitor may help?
Also, many panels have sequencing requirements: does starting the supplies in a different order improve it? (Corrupted EEPROM may affect sequencing?)

[Th3_uN1Qu3]

Re: Samsung LE32R41B foggy picture

Well, before i blew that resistor up on the "good" Tcon, it behaved exactly the same as the "bad" one i just tested in terms of power supply behavior. Also, i don't think the power supplies are sequenced by the Tcon MCU. But as far as sequencing goes, like i said above, what i need to ensure is that AVDD goes up after VGL and VGH do, OR that the panel starts receiving signal before any of the power supplies come up.

Oh, and i just found the auto adjustment function for the VGA input. Took me a while. It was under the "Configurare" (Setup) menu, in the PC submenu, not under "Imagine" (Picture) as expected. Now the picture is no longer slightly offset to the left. I no longer have TV cable in my room anymore (pulled it out 2 years ago), and i don't have a HDMI cable either, so VGA is my only source of input for now.

[Th3_uN1Qu3]

Re: Samsung LE32R41B foggy picture

Haven't kept you updated, have i? That's because i think it's gone for good since last week.

I managed to make the "bad" Tcon power the panel okay, by itself. Then i tried to do the same with the good one, and i had to disable short circuit protection on its power supply otherwise it still shut down.

TV powered on, and... i was greeted by the same picture it had when i first got it. Negative and blurry. Worse, now it's the same when powered externally as well. Crap... I think the panel's still fine and some trace has given up or something, but i've wasted enough time with it.

I shoulda just built my own little power supply for it, and it would've worked.

[Jaco0]

Re: Samsung LE32R41B foggy picture

How did you exactly get rid of the white (GAMMA issue) screen? I'm having the same problem, already replaced the AS15 IC, with no luck. Any ideas?