power supply board BN44-00438B repair

[hienton2]

I have powersuplly BN44-00438B It works but The big cap 450v has only 165v
when on. please help.

http://www.amazon.com/Samsung-BN44-0.../dp/B008DIUKOC

[Glitcher]

Re: power supply board BN44-00438B repair

I suspect the PFC circuit isn't working. I would check the FETs and diodes around the big cap, as well as the PFC driver IC underneath.

[hienton2]

Re: power supply board BN44-00438B repair

Thanks Glitcher.

I see IC gmo465r (faichild) I do not what is this ic.Can not find datasheet.

[tom66]

Re: power supply board BN44-00438B repair

How sure are you about that part #?

[hienton2]

Re: power supply board BN44-00438B repair

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.

May be gmo465r is for 13v and 5v run voltage

[tom66]

Re: power supply board BN44-00438B repair

That is PFC controller; have you checked Vcc voltage?

[hienton2]

Re: power supply board BN44-00438B repair

Yes I have 15v at pin8 of ic pfc.
pin 1 of this ic has 1v.

[tom66]

Re: power supply board BN44-00438B repair

Is PFC diode (usually on heatsink) not shorted? Are current sense resistor(s) (<1 ohm usually) both OK?

[hienton2]

Re: power supply board BN44-00438B repair

I see white 5W resistor connect to fet of PFC .It is ok,. I check all diodes . They are OK. I do not see diode for PFC ckt on heat sink.

[gruv2ths]

Re: power supply board BN44-00438B repair

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.

[stj]

Re: power supply board BN44-00438B repair

can i just ask what the mains voltage is in your country?

[gruv2ths]

Re: power supply board BN44-00438B repair

can i just ask what the mains voltage is in your country?

110 VAC

Thanks!

[tom66]

Re: power supply board BN44-00438B repair

That is fine then but it should rise once the TV turns on. Rise to about 390V.

[gruv2ths]

Re: power supply board BN44-00438B repair

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?

Thanks!

[tom66]

Re: power supply board BN44-00438B repair

390V or so with a tolerance of about ±15V.

[gruv2ths]

Re: power supply board BN44-00438B repair

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.

[gruv2ths]

Re: power supply board BN44-00438B repair

Hey guys,
Sorry about all the nube questions.

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?

What I wouldn't give for a schematic! LOL

[tom66]

Re: power supply board BN44-00438B repair

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.

[gruv2ths]

Re: power supply board BN44-00438B repair

OK great info thanks!

Also, since my 5VA is only 4V, is that enough V for the logic to run on the main board? (it stays 4V with or without that main board connected)

[tom66]

Re: power supply board BN44-00438B repair

Hmm, is the 4V steady or unstable? 4V is probably not enough.