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Nightmare Samsung PTV

This Samsung HCN4767W projection set is really making a nuisance of itself. It had a blown convergence IC when I acquired it, so I replaced them both. It ran for a few days in the shop (about 6-8 hours a day), then blew one of the same IC's again. I replaced them again, and also replaced the convergence processor board. Again, it seemed to work fine for a few days, but now the bloody IC's have blown again. The supply voltage to the IC's is a solid 25V (pos. and neg.), well within the 50V max. supply voltage the IC's are rated for. Both IC's are properly heatsinked, though they seem to run quite hot - I assumed this was just normal. I've also gone through the convergence board and power supply looking for caps up in ESR, but found none. The replacement IC's were supposed to be OEM, but I have to wonder just how compatible they really are. It's the only explanation I can think of. I'm tired of wasting time and money on this piece of junk. Unless I can be certain any further replacement parts will work, I'm going to scrap it and take my losses, which would be close to $300 as of right now. I will also vow to never gamble on a Samsung again - they're nothing but trouble. Any advice would be appreciated

Reply to
Chris F.
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Usually these problems are due to the static centering rings on one or more of the CRTs being misadjusted and the convergence IC has to put out a steady DC component to correct it. If you scope the outputs from the convergence IC and see both positive and negative current swings into the convergence magnets, everything is OK. If not, you need to adjust the centering magnet(s) on the appropriate tube(s) and then re-converge the set.

David

Reply to
David

Certain Samsung models were pretty popular for this. I take it by your knowledge that you've worked on a few.

--
Live Fast, Die Young and Leave a Pretty Corpse
Reply to
Meat Plow

Yes, but those were not the only sets with this problem. There were quite a few Sony sets as well. If the convergence ICs are running hot, the scope comes out and 9 times out of 10, fixing the static centering and re-convergence clears the overheating.

David

Reply to
David

Makes sense. I'd have to assume these were factory defects that resulted in the sets affected to work for a couple years. Or do the static adjustments somehow move on their own due to heat/cool cycles? I know on my Panasonic 51" PTV the screws holding the convergence ICs were laughably loose when I replaced them in 2006. The set worked fine from

1999. And has worked fine since the repair. I used a little compound on the screw thread and a dab of glue on the heads after I torqued them down so they wouldn't walk back loose which is what I theorized happened. No way would the amps have lasted 6+ years as loosely set to the heat sink as they were. 
--
Live Fast, Die Young and Leave a Pretty Corpse
Reply to
Meat Plow

Hate to sound like Joe Obvious, but where did you get the 50V max from and is that max for each input voltage or a potential across them?

The one thing that jumps out with the above is, +25 and -25 gives a working voltage of 50V, if you see what I mean.

Just saying, even if each leg was only a volt high (instead of +24/-24), given the amount of current those things draw, probably adds up to a few watts of less heat it has to get rid of.

Just throwing a thought out.

-bruce snipped-for-privacy@ripco.com

Reply to
Bruce Esquibel

Never thought of that. It actually specifies +/- 20V on the board itself, however I was measuring this with the convergence board disconnected - not sure what the actual voltage is while under load, and now I'd have to replace the IC's again to find out. Not sure if I want to gamble another $50 on this thing or not.

Reply to
Chris F.

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Your convergence amps are probably working too hard. They may be running like an audio amp with the volume turned up all the way all the time. If this is what's happening you need to do geometry alignment. you might start by completely disconnecting the convergence circuit and centering beam landing with the crt neck magnets. You will definitely need a service manual or a memory better than mine to do geometry alignment. I seen units of many brands come out of the factory with geometry alignment so bad that the autoconvergence won't work. With good alignment the convergence amps don't dissipate as much power as with poor alignment. good luck.

Reply to
Scot

I think I have this straightened out... I hope. After installing the two new convergence IC's, I was surprised to see the exact same symptom. I pulled the convergence processor board, which I had newly replaced, and saw a burned zener diode. I replaced it with one from the old module, and everything seemed back to normal. But to be certain, I reset the convergence to factory default and started over. I also attached ammeters to the +25 and -25 supplies going to the convergence output board, to monitor the current as I made the adjustments. Once the convergence adjustments were done, the current draw was about 600mA on each supply, at 23V. The IC's were still quite hot, and I realized that this was due to poor design: both were bolted to a single, thin heatsink which mounts to the steel frame. Very little heat was getting transferred to the steel frame, even though everything was mounted properly. So what I did was remove the module from the steel frame, and bolted a much larger heatsink to the existing one, and mounted everything to the side of the cabinet. The IC's run much cooler now, and hopefully this will prevent them from failing again. I've learned a few things from this, the most important being to never gamble money on a Samsung. Once this TV is sold I hope I never see it again.

Reply to
Chris F.

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