Samsung bn44-00623b help

[Dannyx]

Good day folks. In this "episode", I need a bit of advice with this power supply: bn44 00623b. Can't find a bloody schematic :|

Problem is as follows: when I got it, ICM801CS (a FSFR1800 HSL) was blown. Other than that, nothing else appeared faulty - no shorts or anything. I replaced it and I tested it out using the lightbulb just to be safe. The bulb doesn't indicate any issues (as much as a bulb can do that ), the relay closes, I get 330v on the main caps and that's it: no output and no PFC. As far as I know, Samsung PSUs start with no main board connected, so this one SHOULD do that too and sure enough, I do see around 3v on the ON-OFF pin. Part of the problem is that I don't get 18-19v on the VCC pin of the PFC IC - I only get 5v which is not near enough. I checked the resistors around QS801 (a KTD1624 apparently, after a LOT of searching). This QS801 should control VCC for the switching ICs and I get 5v on its base, 18v on the collector and 5v on the emitter (which runs to the ICs).

I then tried "forcing" the PFC to turn on by turning on that transistor no matter what, so I removed the jumper going between the base and RM817 which goes to GND. This indeed turned on the required 18v, but my bulb also came on bright and steady and the capacitors only reached around 90v - definitely not OK and I'm not willing to risk putting this setup on mains Could it be because of the bulb ? Does an APFC circuit start up normally with a series lightbulb ? My guess is the caps fail to reach the required voltage so the PFC IC keeps "pumping" to try and do so, which draws current and keeps the bulb on....not sure :|

Anybody got any "bright" ideas or test suggestions ? Any help is greatly appreciated.

[Dannyx]

Re: Samsung bn44-00623b help

HA ! After some more digging, I managed to find the schematic AND the defect It's not the EXACT model of PSU up to the letter, but it's as close as we're gonna get - see it attached below.

The defect comes down to ICM803, a KIA431 adjustable zener diode, becoming shorted cathode to anode, thus pulling the base of QS801 to GND. Now I'm waiting for a replacement to arrive and hopefully it works. If it does, this hopefully helps someone else who may have this problem, since I haven't found too much about this PSU or its possible defects. The modest experience I have in the field, tells me it's equivalent to a TL431 which does the same thing.

[budm]

Re: Samsung bn44-00623b help

That IC is used for over current sensing shutdown if FSFR1800 has over current draw.
I would also check RM812, DM802, DM805 to see if they are damaged or not.
When that ICM801 went bad, it probably dumps High Voltage to the CS pin.

[Dannyx]

Re: Samsung bn44-00623b help

I replaced that TL431, but the thing STILL won't fire up: I now read around 7v on the VCC pin of the PFC IC (and on the base of QS801), instead of the 5v I got initially. Something's still fishy and I believe it's DM802 indeed: even though it's a diode, it didn't fail shorted, it apparently failed OPEN, because I get absolutely no reading across it in any direction, so I believe that's my next stop.

[Dannyx]

Re: Samsung bn44-00623b help

Replaced DM802...STILL 7v on VCC...what's going on here ?

[Dannyx]

Re: Samsung bn44-00623b help

Found RM812 open-circuit....this thing is riddled with small dead parts :| Every time I replace something, I seem to track the missing "on signal" closer and closer to the IC that blew.

I'm still not sure how the TL431 is used in this setup: doesn't its "zener voltage" DECREASE when voltage is applied at its REF pin ? How come the circuit is not starting even when the voltage at REF is missing or low ? Shouldn't this have the opposite effect and INCREASE the "zener voltage", thus providing enough base drive to Q801 to run it ?

[budm]

Re: Samsung bn44-00623b help

In normal operation that TL431 is not active.
You can remove RM817 so the TL431 will no longer able to clamp down the QS801 16V linear regultor circuit and then you should see about 16V between the Base of QS801 and primary side circuit GND.
If you do not see that 16V or so on the Base them you need to test ZDS84B16, OPTO PCS802S, RS808, QS801, etc, in that section.
BTW, what DCV do you have feeding the Collector of QS801?
The resistance reading between primary circuit GND and the Emitter of QS801?

[Dannyx]

Re: Samsung bn44-00623b help

In normal operation that TL431 is not active.
You can remove RM817 so the TL431 will no longer able to clamp down the QS801 16V linear regultor circuit and then you should see about 16V between the Base of QS801 and primary side circuit GND.
If you do not see that 16V or so on the Base them you need to test ZDS84B16, OPTO PCS802S, RS808, QS801, etc, in that section.
BTW, what DCV do you have feeding the Collector of QS801?
The resistance reading between primary circuit GND and the Emitter of QS801?

I know for a fact QS801 is fine, because I removed the jumper marked in the pictures of my original post and PFC started up, keeping the lightbulb on, which although made me think something was faulty, may be perfectly normal with a series lightbulb, since it does the same thing with a functional PSU.

The emitter voltage is around 18v on QS801 and just today I checked just about every SMD component left in that area and didn't notice anything off, aside from that open resistor of course which shall be replaced ASAP....haven't analyzed the schematic deep enough to actually know WHY an open resistor there would cause the lack of base drive on QS801, but it's still a fault which must be corrected. Like I said, every time I replace something, I seem to notice something else....

[budm]

Re: Samsung bn44-00623b help

Removing the jumper is the same as removing R817 as suggested, so what Voltage do you get now between Anode and Cathode of Vref diode 431?
68 Ohms RM812 is also connected to CS pin so when that IC shorted out it dump high Voltage on that resistor also, and when the resistor is open instead of haveing 68 Ohms GND for the Vdrops, the Vdrops will be higher and enough to feed DM802 to turn on the 431.
I also wonder now as to how close the circuit for the 00622b to your 000623b.

[Dannyx]

Re: Samsung bn44-00623b help

I also wonder now as to how close the circuit for the 00622b to your 000623b.

I'd say they're identical as far as the primary is concerned, since I was able to follow along very closely and all the parts match. Perhaps something on the secondary is different, but I don't care about that ATM...maybe something about the LED driver is different, since it could be designed to drive a different amount of LEDs and some of the components may be under/oversized/missing, like many Vestel PSUs do: they'd use the same board for various TVs and just have unpopulated areas depending on the application.

[thoma]

Re: Samsung bn44-00623b help

http://www.ohmsupplies.co.uk/epages/...roducts/KIT433

http://www.ohmsupplies.co.uk/epages/...roducts/KIT434

[thoma]

Re: Samsung bn44-00623b help

http://tel-spb.ru/remont-tv-lcd/samsung-ue46f6510

https://www.youtube.com/watch?v=uIrlbsbiltY

[budm]

Re: Samsung bn44-00623b help

I'd say they're identical as far as the primary is concerned, since I was able to follow along very closely and all the parts match. Perhaps something on the secondary is different, but I don't care about that ATM...maybe something about the LED driver is different, since it could be designed to drive a different amount of LEDs and some of the components may be under/oversized/missing, like many Vestel PSUs do: they'd use the same board for various TVs and just have unpopulated areas depending on the application.

At this point replace that 68 Ohms resistor and measure the Vdrops of that 431.

[Dannyx]

Re: Samsung bn44-00623b help

I'm trying, but my buddy got the wrong ones I snapped him a picture of the original which says 560 on it (56 ohms, slightly different from what the schematic says, but NVM) and he got me some 680 ohm ones (681 written on them)...funnily enough, the schematic says 68 ohms and the ones he got are 680 ohms, so he must've messed up that last digit (the multiplier), although I DID tell him exactly what's written on the original and never mentioned 68, so this is turning into a marathon of screw-ups

[Dannyx]

Re: Samsung bn44-00623b help

I replaced RM812 and the voltage went up a little bit more, to almost 9v, but it's still not OK....WTH ?! Now what ?

[Dannyx]

Re: Samsung bn44-00623b help

Here's another thing I tried: I removed the jumper going between the REF of the TL431 and DM805 (page 3 of the schematic, although not marked as a jumper, it's essentially the line running parallel to the thick GND trace towards the bottom) and I STILL get no output, so there's something wrong in the REF section (the cluster of components to the left of the page, close to the TL431), because if I remove the jumper I showed in my original post, PFC DOES come on.

[Dannyx]

Re: Samsung bn44-00623b help

Ok, I got it going now. Guess what the big issue was: that ICM803 is a KIA431, whereas the one I installed was a TL431 - I mistakenly told my buddy it's the same thing when I sent him to get some. Although they're both identical in specs, they have the REF and CATHODE pins reversed, so what was happening is I was sending the control signal into the CATHODE pin and the "output" to the base of the transistor was on the REF pin.....of course it wasn't gonna work, so I removed it and flipped it around, not having an actual KIA on hand (looks a bit dodgy but hey hey), and the PSU fired up ok.

One thing which is not quite to my liking is that after letting the board run on its own on the table with nothing connected, in which time I also took some measurements, the main IC I replaced (ICM801S) got quite warm to the touch, even though technically it wasn't doing any heavy work. I only noticed when I picked up the board to solder in the heatsink (since I didn't want to bother nailing it down only to have the IC blow again and waste extra time on those big beefy pins). The heatsink WAS attached to the IC with the screws mind you, just not to the board too...if it got relatively hot with no load, I can imagine when that backlight comes on, that's going to be cooking in there.....would this be a reason for concern or is this relatively normal ? :| Perhaps some other "power" components like a snubber or something is causing issues ? I don't want to go around blindly replacing parts either.....

[Dannyx]

Re: Samsung bn44-00623b help

Problem no.2: the 12v output is low. Under no load, I get 14v, when the thing powers on and the backlight comes on, it drops to 9v.....damn me...

[Dannyx]

Re: Samsung bn44-00623b help

UPDATE: realising there's probably something wrong in the feedback circuit, I followed along with the schematic and found DM804 open circuit. It's a BAV70. I'm not entirely sure why an OPEN diode would cause the feedback to malfunction...it's in parallel with the optocoupler, so there's probably some explanation.

EDIT: changing it didn't improve the output....

[joe-joe]

Re: Samsung bn44-00623b help

if you want i have a brand new power supply bn44-00623b!