Samsung LN46A650 with suspected video processor issues

[hardwareguy]

Im at a friends place messing with his busted LN46A650.

The TV will turn on just fine. When an HDMI signal is given, the TV will have massive video corruption and a give a buzz through the speakers. When composite is used, sound and video are noisy and the TV will lock up (you cant eve power it down!) within 10 minutes.

The caps are GOOD....I suspected the Samwha caps and he ordered some UCC and Nichicon replacements but when I pulled the SamWhas and threw them on the BESR meter, they were in excellent condition.... 0.05 ohms or less.

In any case, the PSU has been fitted with higher ripple rated, equal ESR Nichicon and UCC caps.

PSU voltage outputs seem to be in spec.

The PSU makes a faintly audible buzz/hiss. I suspect this is the CCFL inverter.

So should we change the video input/processor board now or should I check other things?

[hardwareguy]

Re: Samsung LN46A650 with suspected video processor issues

OK this is freaking weird..... I have MASSIVE ripple on the +13V rail when thigns go freaky.

When the TV works, the 13V rail is clean!

Now what could be causing this? The solder joints look OK.

[Wizard]

Re: Samsung LN46A650 with suspected video processor issues

13V measured the ripple WHERE?

Cheers, Wizard

[hardwareguy]

Re: Samsung LN46A650 with suspected video processor issues

Oops its the +5V line that's doing this weird crap.

[kc8adu]

Re: Samsung LN46A650 with suspected video processor issues

measured on the psu?
had a bad rectifier on a sanyo that was intermittant.+5 was going noisy but +12 went high.the plastic seperated from the tab when i pulled it.

[Wizard]

Re: Samsung LN46A650 with suspected video processor issues

Resolder the whole 5V circuit on that SMPS and probably better replace the diode (this is two diode in one TO-220 package if this one uses this. Otherwise a diode.

Cheers, Wizard

[hardwareguy]

Re: Samsung LN46A650 with suspected video processor issues

This was measured on the video board very near the PSU input connector on a trace directly connected to the power connector.

The pulses Im seeing when it goes bonkers are pretty big....+/- 1V or so and they dont look like random noise, they look like regular spikes on the scope with the time slice set to 0.1ms/div.

Zooming way into the uS/div range and the pulses look like some messed up sine waves that are out of phase.

When the TV is operating fine, none of this exists.... it's practically textbook DC on the scope.

The entire LV section minus the SMT parts has gone through a solder sucker and had new solder applied. It had some of the nastiest looking ROHS joints I've seen in a long time. Dull gray everywhere! Under a really strong light some looked like they would go soon but none looked like they had failed outright.

[hardwareguy]

Re: Samsung LN46A650 with suspected video processor issues

Oh and bear with me as this is only the 3rd TV I've seriously attempted to fix....PCs and stereos are my specialty.

[hardwareguy]

Re: Samsung LN46A650 with suspected video processor issues

The TV ran all night long with no issues.

Tests will continue until this evening.

[PlainBill]

Re: Samsung LN46A650 with suspected video processor issues

The TV ran all night long with no issues.

Tests will continue until this evening.

They wait to fail until you've put the back on and the guy has his wallet out to pay you.

PlainBill

[hardwareguy]

Re: Samsung LN46A650 with suspected video processor issues

The TV ran for over 30 hours and has still performed flawlessly. I hope it holds up.

[hardwareguy]

Re: Samsung LN46A650 with suspected video processor issues

AHHHHHH! CURSES!

It's broke again...... Set exhibits one or two thick white lines down the screen that sometimes flicker, the picture may freeze and the set may power cycle on its own.

The defect log contains the following entries:
0 IIC ERROR!! 0x9C MST3560 Write
1 IIC ERROR!! 0x9C MST3560 Write
2 IIC ERROR!! 0x9C MST3560 Write

What pisses me off is that when we take the back off it doesn't do it nearly as much. Im not a drinking man but if this keeps up I'm gonna need a beer!

Im leaving the scope with my friend so he can monitor it when it goes bonkers. Ripple is very low right now (unmeasurable with my scope) but then again, the set works right now.

[Wizard]

Re: Samsung LN46A650 with suspected video processor issues

I really want you to fix the SMPS first. by change the diode for that 5V and resolder the coils that is in between two capacitors. New capacitors on both sides of that coil for that 5V?

Noisy SMPS makes mianboard to go crazy. MST3560 is a ADC (analog to digital converter) IC for component and VGA inputs, fix the SMPS.

Cheers, Wizard

[hardwareguy]

Re: Samsung LN46A650 with suspected video processor issues

OK I'll let him know. I saved a link to a Vishay datasheet for a suitable rectifier which he can order from Mouser.

I seem to recall that it had caps on just one side of the output inductors..... its not a "nice" SMPS by any means.

The bad thing is when it died tonight I didnt have a scope on the PSU..... and it was doing different things this time. However...I think its related, the errors in the defect log are identical.

[hardwareguy]

Re: Samsung LN46A650 with suspected video processor issues

Rectifiers are in....he'll probably be putting them in tonight.

Ive already given him instructions on how to put them in...and warned him of what will happen if he screws it up. A solder bridge here and....BOOM!

[hardwareguy]

Re: Samsung LN46A650 with suspected video processor issues

Rectifiers changed....still tons of ripple (1V p-p or so)

All solder joints redone.....

What now?

[hardwareguy]

Re: Samsung LN46A650 with suspected video processor issues

His granddad, the owner of the TV is on a warpath for a new TV....were trying to save it.

Hopefully it goes to my "recycling center"....aka I fix it and my friend gets the TV.

[Wizard]

Re: Samsung LN46A650 with suspected video processor issues

Which 5V making noise? There are 2 5V circuits, one for standby power only and other one run 5V shared with big transformer for other 12V/13V? The standby power SMPS is very small transformer with 8 pin IC.

So I ask which 5V?

Cheers, Wizard

[hardwareguy]

Re: Samsung LN46A650 with suspected video processor issues

Ill have to have him double check but I think its the main 5V rail.....ill have him trace it.

[hardwareguy]

Re: Samsung LN46A650 with suspected video processor issues

Hold on....Im almost dead certain its the main 5V! I remember my scope trace being flat when the set was off!

It sucks being 200 miles way from a TV you are trying to fix.....