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Hitachi 42HDT79 - Power supply occasional clicking & whi

 
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tferris



Joined: 20 May 2010
Posts: 3

PostPosted: Thu May 20, 2010 9:28 pm    Post subject: Hitachi 42HDT79 - Power supply occasional clicking & whi Reply with quote

I have a Hitachi 42HDT79 (mid 2006), which recently had the digital main board fail. It was doing the classic screen cycling every 10-15 seconds with the flashing blue light issue and the main board leds just kept cycling all the time (screen power on or off)

I replaced the board (JP50763) with a new one from Andrews Electronics (Link to part).
The board had firmware version 1260 on it which appears to be the latest. (I checked JBMAudio site and the latest he has posted is 1252)

The TV works great now. The TV guide is working again (It was crashing the TV on occasion before the board just failed) and haven't had any reboots.

However, now when the TV is in standby, the power supply occasionally clicks and then makes a whining sound. This is the same sound it used to only make when the main power was disconnected. The standy by light stays on and the TV can be turned on normally.

It basically sounds like the power supply is powering down the high voltage side randomly.

When I had the unit open to replace the digital main, I checked the power supply carefully (along with cleaning the dust off everything) and all the capacitors looked perfect except one (it was a 3,300 mf 100v cap on the right side) which had just a slight bit of bulging. I was thinking about replacing that cap, but decided to just run the TV to see if any issues came up.

Given these new symptoms should I replace that cap.? Should I just plan to replace the whole power supply? Should I just not worry about the sound since everything is still working, and wait and see if something happens?

Any thoughts would be greatly appreciated.
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minnie



Joined: 18 Aug 2005
Posts: 2877
Location: Hell

PostPosted: Thu May 20, 2010 10:57 pm    Post subject: Reply with quote

The 3300uf @ 100volts is a common failure on this model.
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tferris



Joined: 20 May 2010
Posts: 3

PostPosted: Thu May 20, 2010 11:21 pm    Post subject: Reply with quote

Will just replacing the cap. solve the problem, or has the failure of the cap. caused other issues that aren't remedied by replacement? i.e. need to replace whole power supply.

The original cap. was a United Chemi-Con KMH series cap that was 30mmx40mm. Looks like the KMH series has been changed to a 35mmx40mm or a 30mmx50mm model for the 3,300uf 100v (maybe to fix this premature failure issue)

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=565-2932-ND
and
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=565-2933-ND

Which one would you suggest replacing with or other suggestions? or does it not really matter as long as it is a good cap...

Thanks
Todd
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luvtv
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PostPosted: Fri Jan 28, 2011 10:45 pm    Post subject: capacitor is the problem! Reply with quote

Yes, it is the 3300uf @ 100volts cap.
I had the exact problems and sure enough the buldging cap was the problem.
I purchased both the Digikey options you were wondering about just to see which would fit better. I ended up using the 35mmx40mm one (I had to gently push a small cap over a little) to keep the height profile the same as the original, but either will work.
The whole repair took me almost no time to do and cost me less than $30 in parts and shipping, and I got the digikey parts in less than 24hrs after ordering them. TV works like new again.
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Indcontrol
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PostPosted: Fri Jan 28, 2011 11:53 pm    Post subject: Power supply on flatscreen TV Reply with quote

Yes ,it seems that capacitors are a common fault on LCD screens

Open the back cover and replace the capacitors on the power supply board by GOOD quality and preferably higher capacitance if it fits in the space

Indcontrol Electronics in Australia Arrow
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Guest






PostPosted: Mon Mar 28, 2011 9:47 pm    Post subject: Re: capacitor is the problem! Reply with quote

luvtv wrote:
Yes, it is the 3300uf @ 100volts cap.
I had the exact problems and sure enough the buldging cap was the problem.
I purchased both the Digikey options you were wondering about just to see which would fit better. I ended up using the 35mmx40mm one (I had to gently push a small cap over a little) to keep the height profile the same as the original, but either will work.
The whole repair took me almost no time to do and cost me less than $30 in parts and shipping, and I got the digikey parts in less than 24hrs after ordering them. TV works like new again.


I tried this fix and it solved some an issue but tv still not working.
Prior to changing cap tv did power up once which also lead me to the cap being an issue.
Will be checking more components on this board .
At least schematic is available on net free.
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tferris



Joined: 20 May 2010
Posts: 3

PostPosted: Thu Apr 28, 2011 12:41 am    Post subject: Re: capacitor is the problem! Reply with quote

Update on the original post.

I ended up just waiting to see if any additional symptoms cropped up. Well, the power supply continued to occasionally click and whine, but everything worked fine. Then about 3 weeks ago the digital main board failed again. Mad Bummer, only got about 11 months out of that one, and another $200 to replace it Exclamation

I purchased a new JP50763 and a new 3,300 100v cap (went with the 30mm x50mm - would recommend sticking with a 45mm or less cap - 50mm is too close to the cover). When I opened everything up, I realized the 270uf, 450v caps also appeared to have a little bulging. So, I ordered a pair of those.

I replaced all three caps and put in the new digital main board.

TV is back to working just great Razz However, I have caught it making the click and whine twice! Shocked Does this mean it will kill this new digital main board? What else should I do? All the other caps on the power supply look good. I didn't check the power supply Vs and Va when I put it back. Should I open things back up and check that? I don't have a scope, so I can't really look at power cleanliness... Should I just send the power supply to one of these reworking shops? But, I am not sure they will find anything, and I have to pay $150... I haven't found anyone selling power supplies new anymore.

Thanks for any suggestions!
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