Samsung BN44-00445C power supply issue

[nicdev007]

Hello all and thanks for the great welcome to the forum!

With the help of multiple community members and some of my own experience I have advanced on the repair of a Samsung PS59D530A5 TV. The power supply - PFC card number is BN44-00445C.
At first the PFC MOSFETS where blown along with a host of other SMD components including the PFC controller IC (20 pin R2A20118). I replaced all components found in a kit form, to be sure (F801S,QP802, QP804, DP802, QP806, QP808, QP805, QP807, RP815, RP806, DP804, DP807, RP803, RP807, RP804, RP808, ICP801). Attached a picture of the components replaced.
After this still no startup of the PFC, so the relay just clicks every 5 seconds as it tries to start the PFC but fails. I followed some advice to pull down the PS_ON line with a resistor to enable me to troubleshoot further the power supply on my bench and it allows me to measure the voltages more easily.

What I did find was that the PFC IC (ICP801) does not actually get powered, I measure 0,5V on pin 20 (Vcc). Unfortunately the circuit diagrams I have found are not of this exact model and it is making the troubleshooting difficult.
When following the VCC of ICP801 i found 2 zener diodes (ZDP801 and 802) in series (marking WF (Y1)) both not measuring ok, I replaced them both to continue the troubleshooting, but in fact the problem is more upstream as the line is not fed with any voltage (photo attached) and without the correct diagram it is proving slightly troublesome.

Any help will be greatly appreciated. It would be a pity to let it go now after all my efforts. Not sure i could anyway
Kind regards
Nico

[lotas]

Re: Samsung BN44-00445C power supply issue

Schematic
https://www.electronica-pt.com/esque...45c-psu-50639/

[nomoresonys]

Re: Samsung BN44-00445C power supply issue

maybe check all solder joints, touch up if needed: https://www.google.com/search?q=exam...ih=607&dpr=1.5

[nicdev007]

Re: Samsung BN44-00445C power supply issue

Schematic
https://www.electronica-pt.com/esque...45c-psu-50639/

Thank you, this is the schema I have also, but it does not correspond to the board unfortunately. ICP802 in this diagram is a 16 pin PFC driver (UCC28061), but on the board it is a 20 pin R2A20118 amongst many other differences. Some parts do correspond but not the part supplying Vcc to the PFC IC.
Regards
Nico

[nicdev007]

Re: Samsung BN44-00445C power supply issue

maybe check all solder joints, touch up if needed: https://www.google.com/search?q=exam...ih=607&dpr=1.5

Thanks for the advice, I have done so, but will go through it again and check if I missed some.
Regards
Nico

[dskall]

Re: Samsung BN44-00445C power supply issue

I wouldn't think it could be that hard to trace out vcc back to main power. Ic801 not powering up? Is yours controlled through a transistor?

[R_J]

Re: Samsung BN44-00445C power supply issue

The source of the VCC voltage is DX801 (standby circuit) CM801 is the vcc filter, Q?802 acts like a vcc regulator and switch, The collector is the main VCC and the emitter supplies the vcc for the pfc ic, the base usually has 2 series diodes to ground, one is a regular diode, one is a zener that sets the vcc voltage (16~18v) The base is also turned on or off with a optocoupler
Start by checking the voltage ACROSS CM801, it should be about 25~30v

[nicdev007]

Re: Samsung BN44-00445C power supply issue

The source of the VCC voltage is DX801 (standby circuit) CM801 is the vcc filter, Q?802 acts like a vcc regulator and switch, The collector is the main VCC and the emitter supplies the vcc for the pfc ic, the base usually has 2 series diodes to ground, one is a regular diode, one is a zener that sets the vcc voltage (16~18v) The base is also turned on or off with a optocoupler
Start by checking the voltage ACROSS CM801, it should be about 25~30v

Thanks R_J for the valuable assistance,
Traced it back as you suggested.
Voltage across CM801 is a bit lower (17.5V). I removed QC802 (Vcc regulator) from the board to be sure and it measures faulty. I checked the other components in the circuit including the Zener and the rest measures ok.
I'll see if I have an equivalent tomorrow and if it will start up correctly. From what I have found the marking on the transistor "YB" is a KTD1624 (EPITAXIAL PLANAR NPN TRANSISTOR package SOT-89 package).
Thanks again for the help. Lost the habit to trace without a circuit diagram, coming back to me slowly ;-)
Best regards
Nico

[captainKKK]

Re: Samsung BN44-00445C power supply issue

Is CP801 intentionally shorted with foil to enable tracing?

[R_J]

Re: Samsung BN44-00445C power supply issue

Is CP801 intentionally shorted with foil to enable tracing?

That's Shopjimmys board picture

[captainKKK]

Re: Samsung BN44-00445C power supply issue

Duh, now I see it.....I am so slow....I could not figure why no one said anything......I got to go take a nap now...

[nicdev007]

Re: Samsung BN44-00445C power supply issue

Hello all,
Thank you again for your inputs to assist with this unit. I changed QQ801 (marking not clear) but it is the regulator transistor for the Vcc of ICP801 (PFC controller). It seems when the PFC blew up it also blew up QQ801, and the 2 zener diodes ZDP801 and ZDP802.
The set now starts up, I have to still do a full test later to see if all functions are working, but that is great progress.
For future readers and information seekers, I replaced the following to repair the PFC circuit:
F801S,QP802, QP804, DP802, QP806, QP808, QP805, QP807, RP815, RP806, DP804, DP807, RP803, RP807, RP804, RP808, ICP801 -> Repair Kit
and
ZDP801, ZDP802 and QQ801 in the standby powersupply circuit.

One more question for information: What RTV glue do you use to replace the white RTV put on the MOSFETS? Brand or reference could be helpful ? I had an old tube that is no longer manufactured so I wanted your opinion on a good product to use.
Regards
Nico

[nicdev007]

Re: Samsung BN44-00445C power supply issue

That's Shopjimmys board picture

Correct, it is in better state than the board I repaired, so I used it but just for clarity ;-)

[nicdev007]

Re: Samsung BN44-00445C power supply issue

Hello all,
a quick update. The set restarted yesterday and I could check the screen which had quite a good picture, but during testing different parts, after switching it off, I could not switch it back on again.
When switching it on with the remote or front panel button, I just hear a quick relay click and it stays in standby. I am busy checking the standby power supply voltages to continue the troubleshooting but any ideas from your experience is greatly appreciated.
Does anybody know what the VCC voltage on the PFC ICP801 should be? I know R_J said 16-18V but wanted to be sure
I'm wondering if the transistor I used to replace QQ801 is adapted to the task?
Thank you in advance
Nico

[dskall]

Re: Samsung BN44-00445C power supply issue

What is part# of ICP801?

[nicdev007]

Re: Samsung BN44-00445C power supply issue

What is part# of ICP801?

From memory it is R2A20118 and the technical specification I found says VCC 24V, I suppose that is a maximum value.
Very strange behaviour as the set starts up again for no reason.
When it starts the relay sometimes clicks a few times (4 times) or it just starts up without any issue. When it does the set works perfectly. I measure VS at 217V and VA at 55V and the VCC for ICP801 at 17V. The PFC around 388V.
I think I either have a bad capacitor in one of the standby PSU circuits, or a dry solder joint that I missed (I have repaired quite a few).
Regards
Nico

[dskall]

Re: Samsung BN44-00445C power supply issue

Sounds like bad solder joint. Maybe try tapping around board and see what happens.

[nicdev007]

Re: Samsung BN44-00445C power supply issue

Sounds like bad solder joint. Maybe try tapping around board and see what happens.

I did quite a bit of that, no luck. I did however go over the board again to check for bad joints. While doing some measurement I stumbled upon a strange behaviour.
When I put my multimeter on point 1 in the screenshot (VCC line on the standby powersupply) the set starts every time without fail. I remove the multimeter probe and it clicks a while before starting. Almost like I'm adding some impedance to the line.


Tomorrow i'll start checking some DC caps to see if I find something.

[nomoresonys]

Re: Samsung BN44-00445C power supply issue

yep, check the electrolytic caps and components right by that jumper.

[R_J]

Re: Samsung BN44-00445C power supply issue

Replace them, they will likely check ok but are bad.