What did I probably fry? Samsung HP-S4253

[johnboy1313]

I put a new sub power supply in this set a few weeks ago. I thought I had it working so I buttoned it up and brought it up from the basement. I hooked it to the DVD player and had some sparklies. Here's where my stupidity stepped in.

Because I'm lazy, the cover is a pain to get on and off, and I had just brought it upstairs, I decided to try to play with the Vs (small circle in pic) through a hole in the back cover. Everything was going fine until I apparently touched the heatsink in the large circle in the pic (or something connected to the heatsink) with the screwdriver. There was an arc and a loud pop and the set powered off. Now the standby light blinks and a relay in the back clicks about once every second. I'm hoping I just blew a fuse but I suspect more damage than that. I'm kinda upset with myself for being so foolish and the cover really is a pain to get off so I haven't opened it up to check.

So, how bad do you suppose it'll be when I get in there, if you were to guess?

[tom66]

Re: What did I probably fry? Samsung HP-S4253

You probably shorted the heatsink, which is live, to the case, which is earth.
If you are lucky, you just blew a fuse. Fingers crossed.

[johnboy1313]

Re: What did I probably fry? Samsung HP-S4253

The perimeter screws of the cover all go into plastic but your comment reminded me that there are two screws through the cover into the main. I'm so upset with myself right now. Fortunately, I only have about $62 bucks into this thing.

[tom66]

Re: What did I probably fry? Samsung HP-S4253

Meh, I've done stupid shit before. Liked cracked a 50" plasma screen by stepping on it, accidentally.

[johnboy1313]

Re: What did I probably fry? Samsung HP-S4253

I got the cover off and started looking around. All of the heatsinks on that side of the board show to be connected to ground so it makes me wonder if I touched a leg on the orange cap directly beneath the Vs adjusting screw. With everything but the sub-PSU and the main disconnected from the PSU, Va is fluctating between 60V and 73V, Vs starts at 30V when plugged in and slowly drops as the relay steadily clicks to 15V when the relay stops clicking for a couple seconds and it jumps back to 30V and the cycle starts again. Ve, Vset, and Vscan are all 0V. I suspect the PSU is now fried. Is there a way to force this PSU on like with an LCD PSU?

[johnboy1313]

Re: What did I probably fry? Samsung HP-S4253

I didn't see the burnt spot on the PSU until I posted that pic. It looks like I did touch that cap.

[tom66]

Re: What did I probably fry? Samsung HP-S4253

Careful about Va, possiblilty of 73V damaging plasma panel COF drivers... unrepairable.

[johnboy1313]

Re: What did I probably fry? Samsung HP-S4253

I have the panel disconnected

[tom66]

Re: What did I probably fry? Samsung HP-S4253

You need to trace what goes to that capacitor lead and check what has been damaged.
You can force VSON and PSON high for test purposes.

[johnboy1313]

Re: What did I probably fry? Samsung HP-S4253

On that heatsink directly to the left of the adjusting screw, there are three diodes. On the middle and bottom diodes, the cathodes are connected to ground. Is this common?

[tom66]

Re: What did I probably fry? Samsung HP-S4253

Yes; although you'll find only one is grounded, and the other goes to the transformer, which at DC ohms, looks like a ground (but it's an inductor - part of a transformer.) I'd look around the adjustment area: you may have damaged e.g. the TL431 reference IC.

[johnboy1313]

Re: What did I probably fry? Samsung HP-S4253

Pulled the PSU today and found this. There's a big flash burn on the back of the panel too. Hope I didn't kill it. The area circled in the picture of the front of the PSU is the area burnt on the back.

[tom66]

Re: What did I probably fry? Samsung HP-S4253

Panels are pretty tough, the metal back plate is actually separate from the glass.
All fuses good?
Tested the output diodes?
Check the Vs pot.

[johnboy1313]

Re: What did I probably fry? Samsung HP-S4253

All fuses good. Haven't tested anything else. I'm heading out of town for the weekend this afternoon so I may not get back to this until Monday.

To test the diodes, I need to pull one end out, right?

[tom66]

Re: What did I probably fry? Samsung HP-S4253

Yes, best test with one lead out of circuit for two lead devices or two leads out of circuit for three lead devices.

[johnboy1313]

Re: What did I probably fry? Samsung HP-S4253

It was just a burnt trace. I soldered a jumper in and I'm getting steady voltages at all test points. I haven't connected the panel or adjusted any of the voltages yet but they are all there and the psu responds to the power button now.

[johnboy1313]

Re: What did I probably fry? Samsung HP-S4253

Well I've got it working now. There's some pretty gnarly image persistance that I hope I can adjust out. But that will have to wait until Monday.

[tom66]

Re: What did I probably fry? Samsung HP-S4253

Image persistance has been Yrr and Vset for me usually, on Samsung. I have always been able to adjust it out on these chassis.

[johnboy1313]

Re: What did I probably fry? Samsung HP-S4253

The problem is that the persistent image is the one that was on the screen when I shorted the PSU. We'll see if I can get it to completely vanish. Also, there is no Yrr. Just Va, Ve, Vs, Vscan, and Vset.

[tom66]

Re: What did I probably fry? Samsung HP-S4253

Yrr/Yfr are on the Y-main.

I doubt you burnt in the panel but you can sometimes get IR if the image was on there for a long time. The IR fades away once the panel has done about 15~30 minutes erase (which is done during normal running.) My dad's 50" NEC has poor IR problems, if you leave it on news channel for some time you can easily see the ticker there, it fades away within about 30 minutes though.