samsung y-sus repair assistance please!

[zookeepertoo]

hi, on my y-sus board 3 of the 4 mosfets (748228) have blown. I have removed all 4 and am now looking for other defective parts on the board. Strangely the area surrounding the mosfets when the board is powered up shows predominantly a - (negative) 192v and in a few places -(negative) 67v. This includes the tops of the capacitors around that area of the board. Has anybody any idea which other components to look at to find the faults now please. many thanks for looking Dave.

[rayrod81]

Re: samsung y-sus repair assistance please!

Negative voltages are most likely meant to be there. Plasma y-sustain boards put out a negative voltage to set the bottom of the waveform that is sent to the buffer boards.

[zookeepertoo]

Re: samsung y-sus repair assistance please!

Yes i agree in principal but should i be getting those voltages between earth and
the metal capacitor tops? I have new mosfets ready to install but in my mind i still have a problem to resolve or they will go the way of the originals.
For information the tv and board numbers follow.Your input is very much appreciated.

PS50C96HDX

850HW-YB02

LJ41-05120A
REV 1.3

Thanks Again Dave.

[PlainBill]

Re: samsung y-sus repair assistance please!

Service manual is here, but that doesn't show the Y-Sustain, which is considered part of the plasma panel.

There should be a white label on the plasma panel with the model number of the panel. What is it?

PlainBill

[zookeepertoo]

Re: samsung y-sus repair assistance please!

hi, i thought that 850HW-YB02 was the model number. There is also this
50HD-822841301427(03).

Thanks again Dave.

[zookeepertoo]

Re: samsung y-sus repair assistance please!

This is an image of an identical board and buffers.

[zookeepertoo]

Re: samsung y-sus repair assistance please!

Here is a little more background info.

[zookeepertoo]

Re: samsung y-sus repair assistance please!

Any thoughts Bill.
Cheers Dave.

[PlainBill]

Re: samsung y-sus repair assistance please!

Any thoughts Bill.
Cheers Dave.

Yes. I don't know what is going on here. I've never seen a schematic for a Y-Sustain, and have only a vague idea of what is happening with them.

One of the problems is GIGO. A Google search for the panel model number you gave (850HW-YB02) results in only 8 hits. The actual panel number is probably S50HW-YB02. And I'm not having any luck finding more information on it.

PlainBill

[zookeepertoo]

Re: samsung y-sus repair assistance please!(more info)

Yes i havent found much either Bill. The back panel has ca50c9 marked on it if that means something to you. I`m just going to continue searching online.
Cheers again.
Dave.

[rayrod81]

Re: samsung y-sus repair assistance please!

Ok according to the service manual, which has very little useful information, the -190V is supposed to be there. That is the voltage at which the Vscan alignment is supposed to be. The two surface mount mosfets at the bottom of the y-main create that voltage. As to why you are reading -190V to the top of caps I couldn't tell you. Honestly, it has never occurred to me to measure the top of a capacitor. I can tell you that the three small blue caps on the board should be replaced. There are the 25V 680uf caps at C5300, C5715 and C5709. They are known failure points on these boards and can wreak havoc if they do fail. Also the 2SK2837 and B20NK50Z have been known to fail on these boards also. Usually when I have repaired these I have had to replace all 10 mosfets on the two heatsinks nearest to the buffers and the B20NK50Z. I don't know what to tell you other than that.

[zookeepertoo]

Re: samsung y-sus repair assistance please!

i very much appreciate your helping me out here . i`ll keep you posted.
many thanks Dave.

[zookeepertoo]

Re: samsung y-sus repair assistance please!

The story so far.
All components mounted on the three heatsinks have been removed and tested. Still only the previous three fets show as duff. The exception test wise are the two stth20p03s rectifiers (?). I am unsure how to test those.
I have removed and tested the electrolytic capacitors to infinty and all test good as far as that particular test is concerned alhough i do not have the equipment to properly test them. Any advice as to further tests i can perform please.
many thanks Dave..

[jettboat]

Re: samsung y-sus repair assistance please!

check these locations z diode @ #5502, resistors @ 5508 & 5509, v regulator @ Q 5501 I had these fail on the same y sus, along with fet's mentioned on the two heat sinks common with this board when buffers are toasted

[tiny68]

Re: samsung y-sus repair assistance please!

Ok according to the service manual, which has very little useful information, the -190V is supposed to be there. That is the voltage at which the Vscan alignment is supposed to be. The two surface mount mosfets at the bottom of the y-main create that voltage. As to why you are reading -190V to the top of caps I couldn't tell you. Honestly, it has never occurred to me to measure the top of a capacitor. I can tell you that the three small blue caps on the board should be replaced. There are the 25V 680uf caps at C5300, C5715 and C5709. They are known failure points on these boards and can wreak havoc if they do fail. Also the 2SK2837 and B20NK50Z have been known to fail on these boards also. Usually when I have repaired these I have had to replace all 10 mosfets on the two heatsinks nearest to the buffers and the B20NK50Z. I don't know what to tell you other than that.

Can you confirm what the "small blue capacitors" you are referring to? Are they: C5828, C5018 and C5014 which are all marked "331k 1kV"?

[tiny68]

Re: samsung y-sus repair assistance please!

check these locations z diode @ #5502, resistors @ 5508 & 5509, v regulator @ Q 5501 I had these fail on the same y sus, along with fet's mentioned on the two heat sinks common with this board when buffers are toasted

What should the z-diode D5502 read? I get readings of 0.92V and 0.65V in each direction using the diode setting on the multimeter (tested in circuit).