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I am not sure. I see a small ic Fan7930B may be this ic is used for FPC.
Without main cable to power board It has 13v but big cap has only 165v instead
380v.
That is PFC controller; have you checked Vcc voltage?
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Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
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Hello,
I am working the same power supply. I noticed my standby voltage is only 4V, that sounds not close enough to 5V to me. Also on the scope it appears to be oscillating. I replaced the Fan7930B, it is a PWM with integrated switching fet, same 4V on the standby output. Is the big electrolytic supposed to be at 380V? Mine os only 155 to 160V.
That is fine then but it should rise once the TV turns on. Rise to about 390V.
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The TV wont turn on. I only have a strange 5V standby, nothing else.
Need to go and look at the output of the PFC converter and see if it is a mess or not. Any idea what the output voltage of the PFC is?
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Thanks for that, so it appears in my case the PFC converter is not running.
There is no VCC at the VCC pin of the PFN controller PWM. So now i am digging through the traces to see what powers the chip. Just from a cursory look at looks like it runs through a few optos before it gets to the PWM.
Another question on the subject, I ordered the service manual for this set because i could not find it online. $15 later, i get a file with troubleshooting tips the tend to end in statements like 'Replace Main Board" LOL Is it standard these days for service manuals not to include the schematic?
I have not ever seen one that did not.
After re-reading the comments above, I have a few more questions.
Someone said that the PFC voltage would rise once the TV is turned on.
So i guess my understanding of the sequence of events is all wrong.
It appears that the PFC is kind of Or'ed with the main diode bridge. And the converter that generates the 5V and 13V are driven by that Or'ed voltage.
So if the PFC is not always running, can the 5V/13V converter generate enough start up power to get the set on before the PFC kicks in?
Yes, the 5V/13V will usually run without the PFC under light load (i.e. standby only.) This will provide enough Vcc (from an auxillary winding) to the PFC IC to run.
The PFC power is mostly used for main output for driving the bulbs/LEDs. There will also usually be an "undervoltage lockout" which prevents the main output from starting if the PFC is N.G.
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Hmm, is the 4V steady or unstable? 4V is probably not enough.
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