Samsung HP-R4252 42 in plasma. No picture

[Videojoe]

Picked up this gem on Craigslist for $40 because I've been able to fix 3 out of my first 4 tv's thanks largely to this forum. This one powers up ok with the Samsung chime that I've grown to love but the screen is totally dark. Vs and va are fine. I replaced about 10 caps on the power supply just for fun because it didnt do much for me. Took some additional voltages and found that there are no voltages coming out of the power supply to the main board. All of the other voltages are ok. I'm wondering if there is a history of this problem or if anyone else has encountered this or would it just be easier to replace the power board. By the time I trace out a handful of diodes and other bad parts and order them from digi key and pay shipping and then pray I didn't miss anything, I have to weigh it out as far as time and expense. The board number is BN96-02213A which I see on ebay for $50. There is also a 02213B on eBay but I'm not sure what the difference is. Any help would be appreciated.

[freakaftr8]

Re: Samsung HP-R4252 42 in plasma. No picture

well first of all if you got power and you heard the Samsung chime then the main board is getting power I would try disconnecting the upper buffer bored and then power up and if you still get no picture plug in the upper board disconnect the lower

[Videojoe]

Re: Samsung HP-R4252 42 in plasma. No picture

Ok that makes sense. Not sure why I wasn't measuring any voltage at the main board. Ill try the buffer board when I get home

[Glitcher]

Re: Samsung HP-R4252 42 in plasma. No picture

Can you post some photos of the boards in the tv? Specifically the PSU, Y-main, and Y-buffers.

[Videojoe]

Re: Samsung HP-R4252 42 in plasma. No picture

Yes sir, workin til late tonight but I will post first thing in the morning. And thanks for the help.

[Videojoe]

Re: Samsung HP-R4252 42 in plasma. No picture

I have attached some pictures of the HP-R4252. I'm working on a couple of TV's at the same time and I left out some important info here. I already did replace the upper Y buffer board because 2 of the IC's on the original board got very hot and they ohm'd out to only a couple of ohms. However, the Y main and the lower buffer are Rev A1 and the new upper buffer board is a Rev A4. Hopefully someone can make sense of all this. I've been an electronics tech for 30 years in the RF industry but just recently got the brainstorm of fixing TV's.

[Videojoe]

Re: Samsung HP-R4252 42 in plasma. No picture

I removed the upper buffer and powered up the unit. No change. Got the chime but screen is completely dark. Put the upper board back in and removed the lower buffer. Same result. I'm starting to smell a bad Y Main? Yes? No?

[Glitcher]

Re: Samsung HP-R4252 42 in plasma. No picture

Looking at the boards, that Y-main board has a common fault with the SMD mosfets under the heatsink nearest the buffer board (the bigger heatsink). Some diodes may also be bad. Measure the fuses on the Y-sus and see if any of them are open.

The y-buffer boards usually have a blown IC. See if you can spot any burn marks on them, if not then you would have to test them for shorts.

[Videojoe]

Re: Samsung HP-R4252 42 in plasma. No picture

Glitcher you're pretty sharp. Both of the mosfets looked suspicious to me earlier but they ohm'd out ok gate to drain, and gate to source. After reading your reply I checked them again and drain to source is measuring .5 ohms with the probes in both directions for both fets. I don't have a schematic so I'm not sure what's in parallel with them but I wouldn't think it would be that low. They are both 61FC4's (D5027 and D5028). I'll have to see where I can find those and how much they are. I'll double check the other active devices again to see if anything else went. All the fuses are good, its never that easy for me. I'm fairly sure both buffers are good, they read hi z from the Vcc to Gnd. Can't see the tops of the ICs because they have little heat sinks and goop on them but they weren't running hot anymore. I'll check digi key for those fets and post an update after I install them, unless you think otherwise. Thanks for the assist.

[Videojoe]

Re: Samsung HP-R4252 42 in plasma. No picture

Actually now I'm wondering if those transformers are across those fets. Its hard to tell without a drawing.

[Glitcher]

Re: Samsung HP-R4252 42 in plasma. No picture

Those fets are in parallel, so it'll seem like they are all shorted in you measure one in circuit

Edit: I'm actually talking about under the heatsink, you'll have to desolder two pins to remove the heatsink and get to the 8 or 9 (forgot how many) fets under it.

[Videojoe]

Re: Samsung HP-R4252 42 in plasma. No picture

Ok I see them now. The ones that I can't get to with my Walmart soldering iron. Gonna have to get some more heat here for those posts. Well I hope only one of those feta are blown, they are $14/ea.

[freakaftr8]

Re: Samsung HP-R4252 42 in plasma. No picture

Pull one leg off each mosfet. One will be shorted. Others should be fine.

[freakaftr8]

Re: Samsung HP-R4252 42 in plasma. No picture

Heres a service note I made a while back I have on the this board. Had alot if experience with this particular ysus.



When samsung lj41-02761 buffers short *check d5018 d5009 resistors r5090 and r5028 on lj92-01200a ysus board along with mosfets under heat sync.*
Also sometimes if sustain pulses check D5022 near small transformer.*

[Videojoe]

Re: Samsung HP-R4252 42 in plasma. No picture

Yes freakaftr8 all that is true here. I'm afraid I'm gonna miss one little component. For now I'm going to order these parts and ill repost when I install them. Thanks to all you guys.

[Videojoe]

Re: Samsung HP-R4252 42 in plasma. No picture

Aw geeeeez. As I was adding up the cost of all the parts, I saw a Y main on eBay for $45 + $10 shipping so I bought. It arrived today and I plugged it in and put the rest of the TV back together including the sub chasis that holds the main board. Double checked all my cables and fired it up and BANG! A flash and snap crackle pop from the lower right hand side, behind the sub chasis. I took the sub chassis back off and I'm not seeing anything burnt or anything. What do you think fellas?

[Glitcher]

Re: Samsung HP-R4252 42 in plasma. No picture

Did you also replace or repair the y buffers before putting in the new y main?

[Videojoe]

Re: Samsung HP-R4252 42 in plasma. No picture

No, I had replaced the upper last week, and they both ohm'd out good before I put the y main in.

[Glitcher]

Re: Samsung HP-R4252 42 in plasma. No picture

Hmm, you its possible that you might of gotten a bad Y-main. I would recheck the buffer boards again after that pop.

[freakaftr8]

Re: Samsung HP-R4252 42 in plasma. No picture

Yes as a lower buffer could have now damaged y main again along with upper y buffer as well.