LG plasma MZ-42PZ44 YSUS short

[PowerAmpFreak]

Hello. A main fuse on the YSUS board was blown. Dead short after fuse to secondary ground. See attached pictures.
What's hiding under the big heatsink? A hybrid IC?
Anyone know of "usual" stuff that blow on the YSUS module?
Saw a small electrolyte like 100uF/50V going round top (bad), don't think this cause fuse blow though...
Any input is warmly appreciated.

[cadiman]

Re: LG plasma MZ-42PZ44 YSUS short

If you search old posts for plainbill and myself you will find alot of info on l/g boards. This chip is hard to replace. I have done these and have gotten pretty good at it. I could talk you through it. This ic is 40.00 on ebay. The blown fuse means you need to check the y buffer board for shorts. There is a white sticker on the y sus board with the part number. type the part number in ebay and that board will come up.
The part number for the chip is on the heat sink (type into ebay) should cross to an stk 720 ? This will come up on ebay too. Need to replace caps for 15-18 volt supply to ic Wizard would know the best way to check the buffer board.
Cadiman

[PlainBill]

Re: LG plasma MZ-42PZ44 YSUS short

Hello. A main fuse on the YSUS board was blown. Dead short after fuse to secondary ground. See attached pictures.
What's hiding under the big heatsink? A hybrid IC?
Anyone know of "usual" stuff that blow on the YSUS module?
Saw a small electrolyte like 100uF/50V going round top (bad), don't think this cause fuse blow though...
Any input is warmly appreciated.

You should be able to determine if there is a hybrid under the heat sink by looking at the back of the board. Two rows of pins about 2.5" apart are a good clue.

Someone on eBay is selling the hybrids for $40, but they don't list that as a module they fit. Someone is selling the complete Y-sus on eBay for about $72.

PlainBill

[PowerAmpFreak]

Re: LG plasma MZ-42PZ44 YSUS short

I suspect replacing the entire Y-SUS board will be needed.
Of course some questions arise:
What may cause the Y-SUS board go short?
Should a new Y-SUS board bring the tv back into operation?
I don't want to end up placing a new board and just hear it boom again...
Could the panel itself be bad and short out the Y-SUS board which then fails?
Could a powersupply problem end up in a shorted Y-SUS board? The output voltages from the powersupply is measured and seems ok.

[PlainBill]

Re: LG plasma MZ-42PZ44 YSUS short

I suspect replacing the entire Y-SUS board will be needed.
Of course some questions arise:
What may cause the Y-SUS board go short?
Should a new Y-SUS board bring the tv back into operation?
I don't want to end up placing a new board and just hear it boom again...
Could the panel itself be bad and short out the Y-SUS board which then fails?
Could a powersupply problem end up in a shorted Y-SUS board? The output voltages from the powersupply is measured and seems ok.

Y-sus boards can blow by themselves; they ARE handling high voltage and current. They also interact strongly with the buffers. The Y-sus board plugs into the buffers. Check each of the chips on the buffer boards carefully for damage - in particular a pinhead sized crater blown in the top of one. If you don't find any sign of damage you have a decision - replace the buffers anyway, or risk blowing the replacement Y-sus.

PlainBill

[NxB]

Re: LG plasma MZ-42PZ44 YSUS short

Smell the hybrid IC. If its not burned, you can fix most of the other stuff on the board. Its better than replacing.

[PowerAmpFreak]

Re: LG plasma MZ-42PZ44 YSUS short

No smell. The board is *dead* short zero ohms...
I would need a schematic, this board seems to be in use in many different models and brand names, maybe anyone has a schematic for it?
There are a lot of circuits working directly of the VS supply, so there may be hope for a good hybrid after all.

[cadiman]

Re: LG plasma MZ-42PZ44 YSUS short

number one failure is y sus no picture (chip failure) check 15-18v power( marked on baord ) check caps This chip needs larger heat sink, cooling fan
number two failure is z sus... dark picture
third common failure is the control board.. patterns in picture/no picture

Every tv I have replaced ( 4 ) bad z board already had a y sus board replaced
The y sus board is the hardest working board in the tv. Thus the most common failure.

Do you want to learn something or just fix the tv?

If you want to learn, replace chip and see what happens

If you just want to fix the tv replace the y sus board and the buffer board.

If you have never seen this tv working you may find it working with a screen that has some burn in.


Plainbill and Wizard always have the best advice.

Cadiman

[PlainBill]

Re: LG plasma MZ-42PZ44 YSUS short

number one failure is y sus no picture (chip failure) check 15-18v power( marked on baord ) check caps This chip needs larger heat sink, cooling fan
number two failure is z sus... dark picture
third common failure is the control board.. patterns in picture/no picture

Every tv I have replaced ( 4 ) bad z board already had a y sus board replaced
The y sus board is the hardest working board in the tv. Thus the most common failure.

Do you want to learn something or just fix the tv?

If you want to learn, replace chip and see what happens

If you just want to fix the tv replace the y sus board and the buffer board.

If you have never seen this tv working you may find it working with a screen that has some burn in.


Plainbill and Wizard always have the best advice.

Cadiman

Correction!!! Wizard has the best advice. PlainBill sometimes gets it right, also.

PlainBill

[cadiman]

Re: LG plasma MZ-42PZ44 YSUS short

I just picked up one of these with a bad panel. I am gonna check out the boards. let me know if you need anything.

Cadiman

[PowerAmpFreak]

Re: LG plasma MZ-42PZ44 YSUS short

Thanks, I found a cheap YSUS board on ebay. In a few days I know if I need more stuff.

[PlainBill]

Re: LG plasma MZ-42PZ44 YSUS short

Thanks, I found a cheap YSUS board on ebay. In a few days I know if I need more stuff.

Per Wizard, check the y buffers very carefully for any sign of a blown chip (pinhole or crater) before inserting the Y-sus card.

PlainBill

[PowerAmpFreak]

Re: LG plasma MZ-42PZ44 YSUS short

Carefully checked the buffer ic's, no sign of damage. Is it common that buffers go when ysus shorts?
Generally, would someone explain how the bits holds together? I mean all output power that ysus board provides, how is this handled by the buffers?
I can't figure out how on earth the buffer ic's without any heatsinking would have a chance to do high power work..
Plasma is pretty new for me, but been doing ordinary CRT tv service and powersupply service for about 15 years.

[PlainBill]

Re: LG plasma MZ-42PZ44 YSUS short

Carefully checked the buffer ic's, no sign of damage. Is it common that buffers go when ysus shorts?
Generally, would someone explain how the bits holds together? I mean all output power that ysus board provides, how is this handled by the buffers?
I can't figure out how on earth the buffer ic's without any heatsinking would have a chance to do high power work..
Plasma is pretty new for me, but been doing ordinary CRT tv service and powersupply service for about 15 years.

It's amazing to me too. But remember that power handled is not an issue; it's power dissipated.

PlainBill

[cadiman]

Re: LG plasma MZ-42PZ44 YSUS short

I have an insignia (l/g) and it has heat sinks on the buffer chips. It also has a cage blower fan that pulls air through the panel. Very few of these dissipate heat properly as you will see.

[PowerAmpFreak]

Re: LG plasma MZ-42PZ44 YSUS short

Wizard, I wonder how big chance there are that Y buffers are blown as a result of YSUS board failure? I've examined the buffer chips carefully, there are no sign of blown chip. Is it common that the buffer chips are the cause for YSUS board failure?
I just want to get an idea if I dare to put another YSUS board in without changing Y buffers.

[NxB]

Re: LG plasma MZ-42PZ44 YSUS short

Mine looked undamaged and they were fine.

[Wizard]

Re: LG plasma MZ-42PZ44 YSUS short

Ohm the power planes (all of them vs ground), if not too low in resistance, probably ok. Get good YSUS board.

Cheers, Wizard

[PowerAmpFreak]

Re: LG plasma MZ-42PZ44 YSUS short

New YSUS board arrived and replaced. But there are some strange behaviour of the screen. May it be necessary to trim the voltages on the new board?
Here is what happens:
Set comes on, a decent picture shows up, but colours are fading in and out slightly, white OSD text fades from white to red, to blue and back to white...
Is the set all toast?

[Wizard]

Re: LG plasma MZ-42PZ44 YSUS short

Preset the YSUS two pots to exact position as old.

Cheers, Wizard