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Samsung HCN653W - turned on briefly, then shut off   Goto page 1, 2  Next  
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khnitz



Joined: 11 Feb 2009
Posts: 17
Location: Johnsburg, IL

PostPosted: Thu Feb 12, 2009 12:03 am    Post subject: Samsung HCN653W - turned on briefly, then shut off Reply with quote

I am fixing a Samsung HCN653W TV. I have the service manual/schematics and have started digging into it...not much success yet.

My failure mode was that the TV would power up (play it's power-up jingle) then the screen came up with static for about 3s and then it powered off. I can even see Antenna 2 in the upper left-hand corner of the screen during those few moments. I noticed that just before the unit switched off (after the screen has been up 2 or 3s), that the ANTENNA 2 started drifting towards the right - to the middle of the screen...then the TV shut down. I could get the unit to cycle back on and repeat the same behavior after pushing the power button a few times.

The fuse has popped a couple times while trying to find a decent ground for my oscilloscope - I'm using correct 6.3A slow-blow replacements. The TV doesn't cycle to power up (even briefly), now, though there was 5V standby voltage still available. Last time the fuse blew, it took NT801S (5.1Ohm Thermistor) out with it. That Thermistor looked like it had had a hard life, as the PCB was discolored from heat around it, too.

Anyway - BTDT advice on this one is appreciated. I've had success repairing other TVs of mine, just looking for a little advice with this one. I have the tools I need (oscilloscope, multimeter, soldering iron, schematic, etc.). As background, I am an EE and enjoy fixing stuff, rather than pitching it.

Thanks!
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JTS1957



Joined: 21 Jan 2009
Posts: 2395
Location: Far, Far Away

PostPosted: Thu Feb 12, 2009 1:38 am    Post subject: Reply with quote

Isolation Transformer?
kuhurdler



Joined: 28 Dec 2006
Posts: 2879
Location: Overland Park, KS

PostPosted: Thu Feb 12, 2009 6:12 am    Post subject: Reply with quote

pull the degauss connection from the board and try it again.
khnitz



Joined: 11 Feb 2009
Posts: 17
Location: Johnsburg, IL

PostPosted: Thu Feb 12, 2009 10:24 am    Post subject: Reply with quote

OK. I ordered a replacement thermistor (actually 2 so I have an extra) and it should be here in a couple of days.

I'm familiar with how the degauss connection looks for a traditional CRT TV, so far I haven't had to identify it on the rear projection TVs (with individual RGB CRTs) that I've worked on. I'll have a look tonight and post a picture of what I think the connector is that you're mentioning.

Before the fuse and thermistor blew this last time, the unit would only show activity on the Power/Timer LED if the Power button was used on the remote. The LED would come on and flicker while the button was pressed, and then stay on - but no other activity.

More updates to follow...
khnitz



Joined: 11 Feb 2009
Posts: 17
Location: Johnsburg, IL

PostPosted: Thu Feb 12, 2009 10:28 am    Post subject: Reply with quote

Oh, and one more thing...could the Samsung schematics be MORE DIFFICULT to follow?!?! :x

I mean, Sony/Zenith/other schematics have made sense when I've used them. But, there seems to be no link between related pages of the schematic for this Samsung - lines run off the page and to ?? nowhere. :shock:
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Jesse Mack



Joined: 22 May 2008
Posts: 600
Location: The Last Frontier

PostPosted: Thu Feb 12, 2009 12:14 pm    Post subject: Reply with quote

There is no degausing thermister or even a degausing circuit for that matter in all projection tv's.

There are multiple pico fuses on this board, there is a SMPS on this board, so there are two different grounds you have to use depending on what you are trying to measure. If you have no isolation transformer simply check for AC between the ground you want to use and the ground on the Oscope. Measuring the hot ground side of the unit usually only requires a multimeter. For most all other measurements use the tuner shield or measure the resistance between the tuner shield to whatever you want to use as a ground. The resistance must be 0 ohms to qualify for a good ground.

One of the rules of electronics servicing, if you do not want to go backwards, in your endeavor is DO NOT GUESS!!!!


Hope this helps

Jesse

Quote:
The fuse has popped a couple times while trying to find a decent ground for my oscilloscope
khnitz



Joined: 11 Feb 2009
Posts: 17
Location: Johnsburg, IL

PostPosted: Thu Feb 12, 2009 12:49 pm    Post subject: Reply with quote

Jesse, thanks for the advice. Duly noted on the grounds...we used to have isolation transformers for our oscilloscopes in our labs years ago...I don't have one for my home unit, though. I'll pay particular attention to the ground points, going forward.

The thermistor (NT801S) was located between two of the line filters of the AC supply line path (LX802S and LX803S), but before the Bridge Rectifier (D811S). Replacement part is on its way.

No degaussing circuit to check for on this one (or any rear projection, for that matter) - got it!
kuhurdler



Joined: 28 Dec 2006
Posts: 2879
Location: Overland Park, KS

PostPosted: Thu Feb 12, 2009 10:28 pm    Post subject: Reply with quote

Jesse Mack wrote:
There is no degausing thermister or even a degausing circuit for that matter in all projection tv's.


My mistake, I didn't realize it was an RPTV. I wasn't paying attention to the model number. Sorry for the confusion.
khnitz



Joined: 11 Feb 2009
Posts: 17
Location: Johnsburg, IL

PostPosted: Fri Feb 27, 2009 8:07 am    Post subject: Reply with quote

The thermistor finally arrived, I've put it in and am back to square one. I'll start some further investigation today and report back what I am finding.
@jeffbcross



Joined: 01 Jun 2009
Posts: 2
Location: Arizona - US

PostPosted: Mon Jun 01, 2009 9:59 pm    Post subject: Thermistor Supplier Reply with quote

khnitz wrote:
The thermistor finally arrived, I've put it in and am back to square one. I'll start some further investigation today and report back what I am finding.


Where did you purchase the thermistor? I need the exact same part to repair the main power board of my Samsung DLP LED tv, but haven't been able to find it anywhere online.
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