Red and snowy Picture on 50PS3000

[candy-men]

Hey Folks,
I´m still into a fight with the LG 50PS3000.
After replacing all Capacitors on Control Board and all Fets on ZSUS Board, the Picture is still snowy and reddish.
The Voltages are okey so far:
Va= 65,02V (should be 65V)
Vs = 194,96V (should be 195V)
ZBias = 96,7V (should be 97V)
Voltage about the 2,2R Resistor is 0,015V
The Output Voltage to ZSustain is 84V if Screen is bright and 89V if Screen is dark

Can anyone tell me whats going on there? All Fets are new, and all Voltages are present.

Thx so far for your help!

[ReeceyBurger123]

Re: Red and snowy Picture on 50PS3000

Hmm, have you tried turning Vs and Vsc up a little ? Also checked the Vs input fuse on the Zsus ?

[candy-men]

Re: Red and snowy Picture on 50PS3000

Vs is okey , and the fuse is also fine. The output Voltage wouldnt be there if the fuse would be blown.

[ReeceyBurger123]

Re: Red and snowy Picture on 50PS3000

Right, ok the fets you replaced are they on the smaller heatsink ? If so did you check the resistors next to them they sometimes fail O/C ?

[candy-men]

Re: Red and snowy Picture on 50PS3000

The FETs on the smaller heatsink are also new. The heatsink is bigger than the original one. The Resistors are also new. So every Part is new. But the ZSUS Board seems not to work. is there a way to test it?

[Alastair E]

Re: Red and snowy Picture on 50PS3000

I have exactly same set--Had exactly same fault. The VZ-Bias Regulator- 20N25, was S/C Gate Source.

Replaced it--But picked up wrong part. (20N60) Set worked fine for 5 mins till that part went short Source-Drain, also killing the 10 ohm wirewound from Vs.

It also shorted the 20NF20 S-D but Not Gate, by the side of the V-Zbias regulator 20N25. Replaced all three by correct parts. set works with good picture and 97V V-ZBias. but these parts overheat severely, getting to finger-burning temp within 1 minute, (which Cant be right).

Drivers to the 20NF20 replaced--No change. Zener and 1 ohm resistor in reg circuit also OK, as is the tiny 6 legged ant driving the 20NF20 and the Opto, '34H' involved in that circuit.

These three transistors, the Zener, the 10 ohm wirewound, the 1 ohm SMD and all the caps are a known issue--But haven't a clue whats wrong with my set, making these parts overheat like they do!

There should be 98V on the 2W 0.22 ohm resistor pair at the bottom outer edge of the board--this is the V-ZBias voltage. No V-ZBias, You got red mal-discharge.

[candy-men]

Re: Red and snowy Picture on 50PS3000

Try to change all eight 100uF/16V Capacitors on the control Board. This should solve your heating Problem with the Fets. But make sure you take the real Low ESR Capacitors!!!

[Alastair E]

Re: Red and snowy Picture on 50PS3000

Try to change all eight 100uF/16V Capacitors on the control Board. This should solve your heating Problem with the Fets. But make sure you take the real Low ESR Capacitors!!!

OK ok--I'll drag the thing onto bench Yet Again and change the caps--But doubt its those causing the overheating of the V-ZBias reg and or the other two on same heatsink....

Rubycon ZLH 25V 100uF it will get, prob the best in that size I have, and a million times better than the cruddy SMD's in there from LG....

[Alastair E]

Re: Red and snowy Picture on 50PS3000

Changed all the 100uF caps (eight of 'em) and also the 330uF cap on the Control-Board....

That's cured the overheating of the three transistors, and set is working correctly...

Cheers candy-men.

[llonen]

Re: Red and snowy Picture on 50PS3000

I have one of these boards in, do you happen to recall the value of the zener ZD201, and tiny 6 legged ant driving the 20NF20 just in case,

regards

Mark