I am working on this power supply and curious as to how the DC voltage of the rectifier output is increased to what the manual indicates it should be. The manual says the DC output of BD901 should be 320vdc when off and 400vdc when turned on. Now I know the output of the rectifier is only around 170vdc by itself and this is about what I have now, way less then what the manual says it should be and the supply is not working. How does this circuit increase the DC line to 400vdc? My thought was the switching of the mosfet,Q902 but I am not an engineer. Thanks.
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Power Supply Voltage
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Re: Power Supply Voltage
see active power factor correction
Application Note 42047 Power Factor Correction (PFC) Basics
Power Factor Correction (PFC) Handbook Choosing the Right Power Factor Controller Solution
https://cdn.badcaps-static.com/pdfs/...25ddb0846b.pdf
CIRCUITS FOR POWER FACTOR CORRECTION
WITH REGARDS TO MAINS FILTERING
https://cdn.badcaps-static.com/pdfs/...94077c90c3.pdf
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Re: Power Supply Voltage
The explanation in the first post seems a bit wrong. BD901 voltage shouldn't increase much when turned on, however voltage after the coil L903/Q902 drain indeed should go higher when on. So, it means the PFC IC IC902 is not turning on your transistor Q902. Supposedly this should be an automatic world sense (i.e. can detect 120 or 240VAC mains) so that 170V you're getting at BD901 is about right for the US, but the voltage after the coil should go up to that 400V mark when turned on.
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Re: Power Supply Voltage
When the 'STANDBY' pin receives the ON command signal (>2VDC) the switched transistor is turned on to supply the VCC voltage to run the PFC Controller IC.
Do you have better pictures that show the whole page of the schematic?
Upload the service manual will be better.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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Re: Power Supply Voltage
The complete manual was to large to upload so I pulled out the PS page and attached it.
This supply had some damage. ic903 was blown apart and a couple other components in that circuit. Q902 was also damaged so it and ic902 were also changed. ic901 was pulling down the vcc line so it was changed.
Now when plugged in I have app. 4.75v on 5v line. When jumped to standby it comes up to the stated 5v. Q922 is switched on and I have 5v at the vcc of ic902 and ic901. But neither ic seems to be running.
But I think I found out why. In looking at the datasheets for both of these ic's I believe they both need app. 12v to turn on. So I am looking into this now. You are welcome to verify my thoughts with attached datasheets links.
https://cdn.badcaps-static.com/pdfs/...d35c2983cc.pdf Page 7
https://cdn.badcaps-static.com/pdfs/...49ac344075.pdf Page 8Attached Files
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Re: Power Supply Voltage
That is a lot of blown parts, so what DCV do you have on the Emitter pin if switched VCC Transistor Q922?
You are working in the primary side so the GND ref. for your meter will be the negative leg of the main DC filter cap in the primary side.
BTW, can you give the link to the site so I can download the manual?
And what the model number of the TV?Last edited by budm; 03-23-2017, 09:54 PM.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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Re: Power Supply Voltage
It is a Sharp LC-42SB45UT
Complete manual here:
DC is 5v on e and c of Q922 when switched on. 5vdc on e when off.
Yes I am using hot gnd when testing hot side and cold gnd when testing cold side.Last edited by mrtech2017; 03-24-2017, 02:21 PM.
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Re: Power Supply Voltage
5V? The VCC for running the SMPS and the PFC IC is generated by the AUX winding of the standby power supply transformer T904, D908, C965.
So I would check the Voltage of R976 of each end to GND (negative leg of the main filter cap when TV is in standby and when STANdby command is present..
"hot gnd" I hope you mean the negative leg of the main filter cap C907.Last edited by budm; 03-24-2017, 02:27 PM.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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Re: Power Supply Voltage
If you lift one leg of R976 do you then still get about 5V on C969?Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
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Re: Power Supply Voltage
Yes, this was how I found out that ic901 was bad. At first I only had @ 2vdc on this line when Q922 was on and after disconnecting most other components on this line it then came up to the 5v when ic901 was removed. After new ic was installed it held at the 5v when Q922 was turned on.
Last night I lifted 1 side of R976 and connected my external supply and set it at 12vdc and jumped Q922 and I had a good 12v on my vcc's at the ic's. But ic902 was still dead. I have another new ic but have not installed it yet.
I figured that once I see if the PFC runs normal with the 12v supply I will go back and see why there is not 12v on this line.
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Re: Power Supply Voltage
Yes, that is puzzling since you do have about 5VDC standby on the cold side, and there is not much to that circuit at all. I expect the cold side 5V to be really low too since both windings are driven by the same primary drive.Last edited by budm; 03-24-2017, 08:04 PM.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
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Re: Power Supply Voltage
Well i changed out ic902 and with 12v on vcc still no 400vdc. So in looking at the datasheets some more and the schematic it looked like it might need more then 12v to turn on. So I started turning up the external P/S and when it hit app. 12.5vdc the PFC came on and I had 400vdc and the 12 and 24 volt supplies. I think it actually should be around 15vdc on the vcc.
So back to T904 I rechecked voltage at D908 and had 5.85vdc. Lifting R976,R917,R991,R921 it dropped to 3.1vdc at D908. Both D908 and C969 test good and I do not have replacements.
What voltage do you think I should have on T904, pins 4 and 5?Last edited by mrtech2017; 03-26-2017, 09:38 PM.
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