This TV was originally dead. I found the main fuse blown and a dead short across the main filter cap. Eventually traced the short to QL801 and QL802 which I replaced both (NCH, 500V, 4.5A). Now standby voltages are not stable. PFC voltage drifts 389-392V and both 13V and 5V have a slow oscillation (enough to turn on the TV for a few seconds and to read the peak voltage on my DMM). Don't have a scope. Closest schematic I can find online is for BN44-00498A.
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Samsung UN50EH5300F BN44-00499A Power Supply Problem
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Re: Samsung UN50EH5300F BN44-00499A Power Supply Problem
When I first plugged in the board, I did the backlight test and they came on momentarily. I opened up the the panel and confirmed all the backlights are working. I did check a few caps near the shorted FETs and they tested good. I also powered the backlight from the led tester and the tv was showing the logo and rebooting but likely from the oscillating supply voltage. The voltages are being measured with the main board and backlights disconnected.Last edited by neilc6; 02-23-2020, 02:43 PM.
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Re: Samsung UN50EH5300F BN44-00499A Power Supply Problem
The fastguide indicates a 5sec delay for the backlights to come on after the backlight "ON" signal is activated. What is the cycle time?
https://cdn.badcaps-static.com/pdfs/...3db525660a.pdfLast edited by dick_barton; 02-25-2020, 11:47 AM.Willing to help but I'm no expert.
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Re: Samsung UN50EH5300F BN44-00499A Power Supply Problem
I ordered a new board since it is difficult to troubleshoot without a schematic and without a scope. It is cycling on both 5V and 13V outputs with both the main board and backlights disconnected. Probably every 5 seconds. The fast track indicates delay is the bl-on signal from the main board. Interesting observation that the pulled up ps_on signal is a steady 3.3V.
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Re: Samsung UN50EH5300F BN44-00499A Power Supply Problem
Thats the VCC for the pfc circuit, The source for that voltage is from the standby circuit, CS807 supplies the feedback VCC voltage for the standby ic, The elec. cap next to it, CS821 is the filter prior to the QS802 which is the VCC switch.
Check the voltage on CS821.
This schematic is similar, CS803(schematic)=CS807(on bn44-00499), CS821=CP812, CS808=CS821, QS802 is the sameLast edited by R_J; 02-25-2020, 01:41 PM.
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Re: Samsung UN50EH5300F BN44-00499A Power Supply Problem
Originally posted by neilc6 View PostI ordered a new board since it is difficult to troubleshoot without a schematic and without a scope. It is cycling on both 5V and 13V outputs with both the main board and backlights disconnected. Probably every 5 seconds. The fast track indicates delay is the bl-on signal from the main board. Interesting observation that the pulled up ps_on signal is a steady 3.3V.Last edited by dick_barton; 02-25-2020, 02:37 PM.Willing to help but I'm no expert.
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