Samsung PN59D550C1FXZA, X-sustain, shorted fets from bad panel?

[drussell]

Re: Samsung PN59D550C1FXZA, X-sustain, shorted fets from bad panel?

So my question at the time is, does anyone find the 723ohms across those little blue caps suspect, or maybe I'm I getting that reading from other items nearby in-circuit?

To answer this specific question... It depends.

The capacitors themselves should show open circuit but you also need to consider what else they are connected to on the board to possibly account for the 723 ohms. (As an example, a capacitor placed directly across a coil to form a parallel resonant circuit will measure virtually 0 ohms resistance like a direct short because the coil is across it, even if the capacitor is perfectly fine.) If you suspect any of the capacitors themselves and you cannot isolate the rest of the circuit, you would need to test them out of circuit by lifting at least one leg of each one to test across.

You need to investigate where the flash came from and really closely trace out what is connected there because something is seriously wrong if there has been a visible flash. Something has failed catastrophically if there is arcing like that. Something is very fried and there will likely be failures in associated components in the circuit, especially "upstream" towards low energy logic control and driver circuits when you're looking at faults in more energetic "power" circuits.

This is the puzzle part that makes repair "fun".

[DXseekerMO]

Re: Samsung PN59D550C1FXZA, X-sustain, shorted fets from bad panel?

Not sure what you are using to test the IGBT's but to test these effectively it may be necessary use a component analyser capable of driving them as a DVM in diode mode wont always catch a failing device. You might need to construct a test jig for this purpose and that not withstanding you may also need to review the source of the replacement semi conductors you are using.

Right now I'm using a DMM. I get a good diode reading from emitter to collector and I can get the switching function to turn on and off. I just did backlights in a TV that only showed failure when driven by the PSU and this drove home the "need appropriate power" to check these IGBT's. I just don't have a power supply to do that right.

To answer this specific question... It depends.

The capacitors themselves should show open circuit but you also need to consider what else they are connected to on the board to possibly account for the 723 ohms. (As an example, a capacitor placed directly across a coil to form a parallel resonant circuit will measure virtually 0 ohms resistance like a direct short because the coil is across it, even if the capacitor is perfectly fine.) If you suspect any of the capacitors themselves and you cannot isolate the rest of the circuit, you would need to test them out of circuit by lifting at least one leg of each one to test across.

You need to investigate where the flash came from and really closely trace out what is connected there because something is seriously wrong if there has been a visible flash. Something has failed catastrophically if there is arcing like that. Something is very fried and there will likely be failures in associated components in the circuit, especially "upstream" towards low energy logic control and driver circuits when you're looking at faults in more energetic "power" circuits.

This is the puzzle part that makes repair "fun".

Lol...fun! The problem here, really is I didn't do the diagnostic by the numbers. I saw VS voltage come up then drop, saw P-ON? change state like the logic board was shutting the set down and started checking for shorts on VS, VA etc on the Y and X main. Nothing on the Y main was shorted to ground, but VS was shorted on the X main and I said BINGO! I assumed fixing the X-Main would return the set to service. I never considered the Y main because I found no shorts but also never thought about the X-main getting it's power from the Y....until the Y went BANG and I had no happy.

I now wonder if the replacement X main has been damaged by the suspect Y main.

I didn't do it by the numbers. This is why I am where I am. Let this be a lesson to all....do your diagnostic work step by step and by the book. For me to do that I will have to re-solder IGBT's and heat sinks back down to the board that were removed for testing. Time vs. money vs. lack of equipment means I probably should have replaced the Y-main by now.

On the other hand I know all the buffer chips on both scan drives have no shorts and all the components appear to test OK, or similarly to one another when the circuits are in similar configuration. I also re-did all the ground pads on them given the crap grounds I've found throughout this whole TV.

[DXseekerMO]

Fixed!

After replacing both the X and Y sustain boards the TV is working great! It still has a gorgeous picture and after clean-up it looks like new! My only regret was not being able to troubleshoot the original boards through to a finished repair.

A couple questions:

I see what looks like a Wi-Fi module behind the stand, clipped to the stand bracket. Is that what that is, and if so where and how do I access the network features if so equipped?

I also finally realized that THIS IS A 3D TV!!!!! I can't believe it! Does it take the standard Samsung 3D glasses?

Thank you to everyone who participated in this thread and for all of your help.

[Unspun01]

Re: Samsung PN59D550C1FXZA, X-sustain, shorted fets from bad panel?

Definitely a 3D TV. I don't think it's a "smart" TV, but has something called "AllShare" which lets you play media files from network connected devices like PCs and phones, etc.

The manual says wireless is available with an optional Samsung wireless LAN adapter that plugs into USB port... So I'm not sure what wireless device you could have behind the stand.

Even if it was a "smart" TV, and being a Samsung, even if you can access the menu from the TV or basic Samsung remote control, you probably still need a remote from a Samsung Smart TV, with the specific "Smart hub" or "smart menu" button to access any apps