Samsung PS42C450B1W sound no picture

[llonen]

I have had this up and running on test for a little while, Found x-sus board shorted, replaced two fets on Xsus which seemed to solve the problem. anyways lost picture, on start up I am getting three blinks from the power led and a very brief glow from the screen. from there the set continues to start up IE I get sound and controls.

VA and VS test as per panel spec, but obviously drop down rapidly when the protection circuit shuts them down, I have found nothing of note (shorted components) on either the X sus or Y sus boards

regards

[ReeceyBurger123]

Re: Samsung PS42C450B1W sound no picture

Test Vsc, Ve etc also see if Vs has a short to ground on either sus board.

[llonen]

Re: Samsung PS42C450B1W sound no picture

Not finding a short to ground for Vs on either sus board, Ve when as measured from zsus to ground spikes at 80 volts then drops to around 50 volts, I am not finding a test point for Vsc ??

Vsc is that Vscan which measures -107 volts

[ReeceyBurger123]

Re: Samsung PS42C450B1W sound no picture

Right so Ve is jumping about before shutdown ? If so fault remains on the Xsus and it will need retesting. These use combined ERC so Xsus can damage Ysus so I suggest you test both for short circuits.

[llonen]

Re: Samsung PS42C450B1W sound no picture

I will go over the boards again, but did not find any devices that showed up as shorted as per testing on a diode test in circuit, I suppose removal of devices and test on component analyser would be the next step.

regards

[llonen]

Re: Samsung PS42C450B1W sound no picture

Well I have been through the both boards and still find no shorted devices

[llonen]

Re: Samsung PS42C450B1W sound no picture

See attached pictures

[ReeceyBurger123]

Re: Samsung PS42C450B1W sound no picture

So you've also tested all the surface mounted devices ? Also what should the voltages be for the panel for Vsc etc ?

[Hamie]

Re: Samsung PS42C450B1W sound no picture

So you've also tested all the surface mounted devices ? Also what should the voltages be for the panel for Vsc etc ?

Yeah I agree -107 vscan sounds far too low.

Unplug the buffers and see if that goes back up.

[llonen]

Re: Samsung PS42C450B1W sound no picture

I have tested most of the semi conductors, fet's I would not know where to start testing the smd ic's I have checked the majority of the passives on the x board and was making my way through the same on y board, according to the Panel vsc / vscan ? Should be -197 volts.

[llonen]

Re: Samsung PS42C450B1W sound no picture

Will try starting the set up with the buffers unplugged,

[llonen]

Re: Samsung PS42C450B1W sound no picture

Well I have been through the y sus and x main boards, I may have found several open cct smd caps on the ysus board but without a cct I am not able to find what value they should be but I am not getting any reliable measurement from them. Then again I don't have a capacitor / esr meter that will read values this small. Also suspected are several RJP30EZ devices that may be open on one of the junctions.

Thus I may be in need of a source of RJP30EZ three devices
K10A60D two devices
RJP63F3 two device

none of which seem particularly reasonable costed

Any views on the smd capcitors


thanks in advance

[tw2005]

Re: Samsung PS42C450B1W sound no picture

Well I have been through the y sus and x main boards, I may have found several open cct smd caps on the ysus board but without a cct I am not able to find what value they should be but I am not getting any reliable measurement from them. Then again I don't have a capacitor / esr meter that will read values this small. Also suspected are several RJP30EZ devices that may be open on one of the junctions.

Thus I may be in need of a source of RJP30EZ three devices
K10A60D two devices
RJP63F3 two device

none of which seem particularly reasonable costed

Any views on the smd capcitors


thanks in advance

you mean RJP30E2?

RJP30E2 and RJP63F3 are IGBTs. Normally IGBTs fail short from what i've seen.

I have not successfully repaired one of these boards but i did a quick attempt to replace just the failed IGBTs in one xmain resulting in them failing again and both the ymain and xmain boards shorting out.

There's a good chance there's be failed SMD components on the underside like driver ICs, transistors, diodes maybe even resistors.

[llonen]

Re: Samsung PS42C450B1W sound no picture

Many thanks for the information, I have tested what I can of the SMD components on the Ysus board, I am having problems testing the IGBT's, I don't think the fluke is providing enough voltage to turn them on. But can confirm they are not shorted, whether they are open is another matter. Looking at the cost to me to obtain these devices I decided to order replacement boards.

Just as well I checked the replacement boards as I find the Xsus is bad, it has shorted vs to ground, and the IGBT's are shorted. The Ysus looks ok, just as well I checked first now waiting to hear back from the seller.

[Grunder]

Re: Samsung PS42C450B1W sound no picture

Hi Guys, I have a Samsung PS42C430AR with identical Y & X main boards, with the same fault.

ie two blown RJP30E2 IGBT's (Q5003 & Q 5007) on the Y main. In addition the digital isolator U5000 on the Y main has its face blown off.

I dont know if this is totally unrelated, but might help. (did the failed U5000 cause the failure of the IGBT's? or vice versa?)

About to make my post, thanks.

[llonen]

Re: Samsung PS42C450B1W sound no picture

Its been a while, but I am loosing the will to live on this set, sent back one clearly defective X-sus board and just taken delivery of replacement so have fitted what I am told are tested and functional X-sus and Y-sus boards. Both 'appear' ok in as far as I can test the devices. I have checked the y buffer for shorts and find am not finding any. So assembled and tested the set and it is with no real suprise I still get three blinks from the led. the plasma panel appears to flash very briefly, then no further display. I get the Samsung chime and the set is responding normally to the side controls. Vs and Va collapse when the Psu goes into protection mode and Ve still looks unstable.

[llonen]

Re: Samsung PS42C450B1W sound no picture

To move this along, when I unplug the y buffers do i need to unplug anything else or do I just need the buffers disconnected from the Ysus board, as I read conflicting information.

regards

Mark

[Hamie]

Re: Samsung PS42C450B1W sound no picture

Just unplug the buffers.
Have you checked the buffer ICs for shorts?

[llonen]

Re: Samsung PS42C450B1W sound no picture

I did check the buffer panel for shorts but did not find anything, this may of course simply mean my fluke test kit may not be detecting them, ie may be breaking down under higher voltage. I h have Ben assured that both the replaced y sus and x sus are good and certainly I do not find in as far as I have been able to test any shorted devices.

[llonen]

Re: Samsung PS42C450B1W sound no picture

Odly I seem unable to locate any smd fusing on the y scan / buffer I guess it is probably there, I wonder if the I should simply source a replacement y scan card