LG 50PS30 Z-sustain questions

[kingsapper]

Hi All,

I have a LG 50PS30 in near-mint condition given to me by a colleague in it's original packaging (!). On startup it was black screen, but the LED indicator blinked red then went solid blue. I took it apart and consulted the service manual and found the Va and Vs rails were 200mV or so.

After looking around at troubleshooting tips (I'm new to TV's, all my experience is on communications systems and robotics/mechatronics) I disconnected the Z-Sustain board and fired it up. Picture was dim and discolored (a known side-effect of no sustain, I see) but the rest of the system seems to be working fine.

I started troubleshooting the Z-Sustain board (part # EAX55361501) and found that the +Vs rail is short to ground, with a resistance of about .3 ohm. The +5 rail appears to be fine (150k to ground). If the power bus is disconnected, but the control connector is still installed it whines like hell.

There are no bulgy caps, and no damaged components that I can tell.

There are no board diagrams in the service manual for the Z-Sustain, and as TV is not my "first language" I was hoping there were some in the community that could point me to likely culprits on the board.

I've got a full lab to work with.. digital storage scope, analog HF scope, sig gen couple of fluke multimeters and LC meter, hot air rework etc.. so getting down to swap components is not a concern.

Cheers
KS

[tom66]

Re: LG 50PS30 Z-sustain questions

Z-sustain is a common fault of this and its sister the 50PS3000.
There is a repair kit on eBay
http://www.ebay.com/itm/LG-50PS3000-...item3f24baeb63

[kingsapper]

Re: LG 50PS30 Z-sustain questions

Much appreciated for the assistance. I've got a developer's account at a few places so I'll look into the parts and order replacements. I've gotten quotes in the neighborhood of that ebay price for a whole new board!

Thanks again.
KS

[kingsapper]

Re: LG 50PS30 Z-sustain questions

Ok, that being said I just took a closer look at the datasheets on those two MOSFETS.. if this is a well known issue does anyone know why these parts blow up? The manufacturers are reputable, so I'm thinking that there's a design flaw in here. Has anyone published a hack/improvement to prevent it from happening again?

Cheers,
KS

[tw2005]

Re: LG 50PS30 Z-sustain questions

apparently this model 50PS60 also uses the same Zsus.

I have not looked at this, 2 free downloads a day which I've used.

[kingsapper]

Re: LG 50PS30 Z-sustain questions

I have the service manual for the 50PS30 which does not mention the Z-sus at all really.. I was expecting more out of a "service manual" it was actually a bit disappointing. Thanks for the point to the other manual, I may take a look and see if there's any more in that. Thanks for the lead.

Cheers
KS

[tw2005]

Re: LG 50PS30 Z-sustain questions

I have the service manual for the 50PS30 which does not mention the Z-sus at all really.. I was expecting more out of a "service manual" it was actually a bit disappointing. Thanks for the point to the other manual, I may take a look and see if there's any more in that. Thanks for the lead.

Cheers
KS

If it's anything like the one I downloaded for the PJ350, it's more in depth.

[tom66]

Re: LG 50PS30 Z-sustain questions

What is the panel model # for example LG Electronics PDP50E9##### it is printed on the internal metal chassis.

[kingsapper]

Re: LG 50PS30 Z-sustain questions

Panel model is PDP50H30001

Good news about the document being more in depth. Maybe it's just the tech in me, but if something breaks I want to know why it broke and prevent it from happening again. That's the difference between fixed and repaired.. I can whack a couple of FETs in but it's not fixed until the underlying condition that blew the FETs is addressed.

Thanks all
KS

[tw2005]

Re: LG 50PS30 Z-sustain questions

Panel model is PDP50H30001

Good news about the document being more in depth. Maybe it's just the tech in me, but if something breaks I want to know why it broke and prevent it from happening again. That's the difference between fixed and repaired.. I can whack a couple of FETs in but it's not fixed until the underlying condition that blew the FETs is addressed.

Thanks all
KS

Good luck with that thought, it would be nice but i think it's just a fact they fail in service. I don't see any vast improvements going by some posts on the panasonic plasmas. if anything they are tryiing to get the cost down.

pretty sad to read about Sc boards failing under wty with parts supply issues due to high demand. One guy had one replaced 6 months in only to have it fail again 6 months later and now out of wty .

I'd like to know too for my Tv if it was a spec shortfall and maybe beef something up but that's the way it is I guess. So I did the next best thing and learnt how to repair them and now have a little stash for the next failure for mine at least.

[kingsapper]

Re: LG 50PS30 Z-sustain questions

I'm doing failure analysis on the three MOSFETs listed on the repair kit you guys put up over the weekend. That will give me the failure mode, which will send me in the right direction hopefully. It would be nice if it was as easy as a freewheeling diode with a snubber network or something.. I'll post whatever I find.

Cheers,
KS

[kingsapper]

Re: LG 50PS30 Z-sustain questions

Update:
Both of the STF20NF20 NMOSFETs appear to have gone short-circuit. Spare parts have already been ordered, we'll see how things go. Oddly enough the FDP51N25 seems to be fine. I may replace it with a new part just in case it "took a hit". Don't want it to die and take everything else out with it.

[kingsapper]

Re: LG 50PS30 Z-sustain questions

Update:

Three of the GT45F122 IGBT's on the HV side of the board were short as well. So all up, that's 5 devices that shorted. Can anyone suggest a replacement for these? I can't seem to source them from reputable suppliers and am loathe to get them off of ebay. One alternative seems to be the Fairchild FGPF4633, I'm trying to locate some in Australia.

Thanks all, hoping I don't find anything else blown up once I get these repaired.

Cheers,
ks