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HP vs19e LCD - Power transformer problem

 
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edtrussell



Joined: 14 Apr 2008
Posts: 3

PostPosted: Mon Apr 14, 2008 8:49 pm    Post subject: HP vs19e LCD - Power transformer problem Reply with quote

Hi,

I recently replaced the caps on a HP vs19e LCD. Now there is a buzz coming from the power transformer that gets louder when the lcd is turned on or off then gets much more quiet as it runs. Is this normal for a power transformer? If it needs replaced can someone point me to a place that sells a compatible part. Thank you.

Here is a photo of the part

http://i258.photobucket.com/albums/hh253/edtrussell/IMG_0395.jpg

It is the yellow one in the center.
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Mon Apr 21, 2008 7:02 am    Post subject: Reply with quote

Normaly, no buzz should be heard from the transformer of a SMPS. The only sound one has to expect is a high-pitched whistle, in case of older SMPS switching frequency is near or within the audible range.

However, if you hear a buzz, then the transformer itself is probably not at fault.
Check that you don't have too much ripple across the filter cap on the primary side. If one of the diodes in the mains rectifier bridge is open circuit, then it can cause much ripple.
If the SMPS has a wide primary voltage range, i.e. 100-240 V , try running it on another voltage within the range and see what happens.

Make sure that you have used correct types of caps at all positions you have replaced (correct capacitance and low-ESR caps where such parts were fitted from factory).
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MikJank



Joined: 03 Sep 2008
Posts: 2
Location: Belgrade

PostPosted: Thu Sep 04, 2008 6:33 am    Post subject: Reply with quote

Hi edtrussell, is there any chance that you can make the photos of the IC (8DIP) and FET transistor, which are located in the power section after filter capacitor, because one of the mechanics changed those parts and I'm not sure for the values. If you have schematic diagram, or repair manual, of the power supply module, that will help a lot.
Thank you in advance
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MikJank



Joined: 03 Sep 2008
Posts: 2
Location: Belgrade

PostPosted: Mon Sep 08, 2008 7:16 pm    Post subject: Reply with quote

edtrussell, are you still alive?
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Mon Sep 08, 2008 7:26 pm    Post subject: Reply with quote

MikJank wrote:
edtrussell, are you still alive?


As it is a 4 month old post, you may have better luck trying to email him direct
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edtrussell



Joined: 14 Apr 2008
Posts: 3

PostPosted: Thu Sep 18, 2008 9:43 am    Post subject: Reply with quote

MikJank wrote:
Hi edtrussell, is there any chance that you can make the photos of the IC (8DIP) and FET transistor, which are located in the power section after filter capacitor, because one of the mechanics changed those parts and I'm not sure for the values. If you have schematic diagram, or repair manual, of the power supply module, that will help a lot.
Thank you in advance


Sorry, I have since got rid of the lcd. The backlight went out and I gave up on it Sad
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