Samsung LE32R88BD/ BN44-00155A

[julian.p]

Re: Samsung LE32R88BD/ BN44-00155A

Hi everyone, hope you can help me, and that I've posted enough information.

I'm new on here, but definitely not a member of the 'throw it away, and just buy a new one' club, and although I have very little electronics knowledge, I am a keen DIYer, and willing to learn how things work (within reason) and so will 'have a go'.

I have recently suffered a similar power on problem with my 2007 Samsung LCD TV LE32R88BDX/XEU, which is same model and PSU BN44-00155A (Rev 1.1) as this thread.

This was after coming back from a month away, during which TV was powered off and unplugged (usually left in standby mode 24/7), and when first plugged in, it powered up from standby ok with remote control, came on as normal, then after a few seconds, it was put back into standby, but later that day, it would not come on at all.

When AC supply is plugged in, standby light comes on, I/R responds (blinks & goes out) to remote control inputs, but TV won't power up = no picture, no sound, no backlight (and get no response from touch panel control buttons on side of TV).

Have browsed this issue on various TV repair forums, (but Badcaps seems by far away the best!) - where I found this thread, which looks like similar problem.

Have tried the ShopJimmy.com backlight only (LVDS unplugged) and flashlight tests, but get nothing.

Downloaded the Samsung service manual (Elektrotanya.com) for guidance, then took back panel off TV, checked PSU & Main boards for visible signs of burn/damage, but all caps look fine, not blown/leaking.

Have attached pics of TV with back panel off, the PSU & Main Logic/AV Board (BN41-00813B & BN94-01327A).







Used basic multimeter and tested PSU AC fuse = ok, plugged TV in, used remote to power on (standby light off), and tested voltages on PSU Cold side, as follows:

PSU to Logic Board (CNW801 24-pin):
All Pins = 0v except: Pin 1 (PS) = 3.3v, Pin 2 (SB) = 5.2v, Pin 4 (13v) = 0.327v, Pins 7 & 8 (5.4v) = 0.547v, Pins 10 & 11 (12v) = 0.657v

PSU to Logic Board (CNW801 5-pin):
Pin 1 (DET) = 0.023v, Pin 2 (GND) = 0v, Pin 3 (PWM) = no cable, Pin 4 (ADim) = 0v, Pin 5 (BLU) = 0.009v

PSU to Inverter (CNM802 14-pin)
All Pins (1,2, & 5-9) = 0v except: Pin 3 (BL) = 0.008v, Pin 4 (NC) = 0.025v, Pins 10-14 (24v) = 0.106v

So has some power to PSU and standby circuit, but little voltages to either Logic Board, Backlight Inverter, or sound & image circuits.

Thought from this thread it was therefore probably due to failed components on PSU and/or Logic Boards, so managed to get hold of both correct PSU & Logic Boards (used, but guaranteed) for around only £24 ($35), but with replacement PSU installed, get same result, and likewise with Logic Board.

As it's a 12-year old TV, I don't want to throw a lot of cash at it, but would like to fix it and also don't want to be beaten or give up yet, so if it's not the PSU or Logic main board (assuming the ones I got are ok), any ideas on what else could be the problem?

Any help would be much appreciated.

[Agent24]

Re: Samsung LE32R88BD/ BN44-00155A

If you warm the glue with hot air it can be peeled off fairly easily.

[cheeky2]

Re: Samsung LE32R88BD/ BN44-00155A

Its called unsoldering components. If you choose not to take the advice then that's your choice of leaving potentially future failure and other issues with your power unit.
Prevention is better than cure especially when its a 5 to 10 minute job of removing it.

[mac87]

Re: Samsung LE32R88BD/ BN44-00155A

All I can say is you have made a poor job of removing conductive glue! There is still loads left on vital components. Remove it all otherwise it will cause future issues.
Replace with a correct value resistor as to fusible resistors I just use standard resistors of the correct value and rating.

i removed all brown glue that was crushable enough to be removed.

all the yellow glue is hard as rock, I didn' want to degrade working areas trying to remove it.

if you have advices for a method to remove glue and to which components are vital to clean, I'll be pleased to ear those.

[cheeky2]

Re: Samsung LE32R88BD/ BN44-00155A

All I can say is you have made a poor job of removing conductive glue! There is still loads left on vital components. Remove it all otherwise it will cause future issues.
Replace with a correct value resistor as to fusible resistors I just use standard resistors of the correct value and rating.

[mac87]

Re: Samsung LE32R88BD/ BN44-00155A

ok
so I checeked with forced PSU ON (1k resistance between pson and sb)
same thing, no tension 5, 12, 24V only stby tension

then I checked the R801 (0.22ohm Fusible res) , and noted 170 V or something like that
so the Res is open

I desoldered it and discover that it was blown under

so I replaced it with a 0.27ohm that I had in stock

evrything seems to be ok (tensions are ok 12, 24V....) backligth works
it must check that i can use video sources (not possible in my workshop)

do you thing that it is safe to let this 0.27 resistor or I must find a 0.22ohm fusible one ?

[mac87]

Re: Samsung LE32R88BD/ BN44-00155A

hi guys,

I have a samsung LE32R86BD with a power supply board BN44-00155A

the power LED works
the remote controller send signal to the TV, managing to turn off the power led
indicating that the TV is ON
but no image, no back light, (no sound when I press the front buttons)

the PSU board seems OK
even if they seemed ok, I changed the capacitors (*7) of the secondary, and I removed the brown glue from the areas that appeared bad

no change (maybe the red power light seems brighter but not sure about that

with TV on (led off), I tested some points to see if I have tension and the secondary doesn't seem send 24v

BUT I don't really know wich points to measure !

Can you indicate me what points to check in first ?

and what point I need to shortcut to simulate the power on without using the logic board ? (I have seen some linking PSON to 5.2V SB)

I coul send a photo this evening.

[simmo1337]

Re: Samsung LE32R88BD/ BN44-00155A

If you suspected that circuit was causing the problem, all you needed to do was short the optocoupler , that should turn on the transistor if the zener etc. are ok,

Ah yes that would have been a better idea! I did think about that, but I've had no experience with them before and I wasn't sure if they turn into a total short, or they're still slightly resistive when they turn on? However, thinking about it, it would have been a problem since the resistors would have been there

Since I've lost the zenner, I'll have to wait for them to come in the post. Then I'll short the opto out. Thanks again!

[R_J]

Re: Samsung LE32R88BD/ BN44-00155A

If you suspected that circuit was causing the problem, all you needed to do was short the optocoupler , that should turn on the transistor if the zener etc. are ok,

[simmo1337]

Re: Samsung LE32R88BD/ BN44-00155A

Sorry, not too sure what I meant to write there, but just to clarify:

I replaced the safety resistor and still had no 24v output. I then removed the zenner/diode/opto-coupler and biased the NPN with an external 12v and it now works.

So, it must be either the zenner/diode/opto-coupler that's failed

[budm]

Re: Samsung LE32R88BD/ BN44-00155A

I thought I'd just let people know, in case it happens to them, but it seems like either my Zenner diode (ZDB805) or signal diode (DB804), or the opto-isolator (PC801S), failed. I removed the zenner (and unfortuanlty dropped, and lost it) and the signal diode, and biased the base of QB802 with an external 12V supply (I don't have a 15V) through a 2.2K resistor. I also removed RB808, so that I could apply 12V without the resistors affecting it and dividing it down.

Doing this worked! So, it seems, that the failure was in RM801. I replaced this, but still had no 24V output, until replacing the aforementioned components. I think the signal diode is okay, so it's likely to be the Zenner or the Opto Coupler. I've got new ones on order and will post back when I know exactly which one failed.

Thanks for the help!

So what is the "I replaced this, but still had no 24V output, until replacing the aforementioned components." that you replace to get the 24V working, the Coupling/blocking cap that mention?

[simmo1337]

Re: Samsung LE32R88BD/ BN44-00155A

I thought I'd just let people know, in case it happens to them, but it seems like either my Zenner diode (ZDB805) or signal diode (DB804), or the opto-isolator (PC801S), failed. I removed the zenner (and unfortuanlty dropped, and lost it) and the signal diode, and biased the base of QB802 with an external 12V supply (I don't have a 15V) through a 2.2K resistor. I also removed RB808, so that I could apply 12V without the resistors affecting it and dividing it down.

Doing this worked! So, it seems, that the failure was in RM801. I replaced this, but still had no 24V output, until replacing the aforementioned components. I think the signal diode is okay, so it's likely to be the Zenner or the Opto Coupler. I've got new ones on order and will post back when I know exactly which one failed.

Thanks for the help!

[simmo1337]

Re: Samsung LE32R88BD/ BN44-00155A

Sorry, what I meant was I put a resistor from pin 1 to pin 3, to try and emulate the on switch. However, j no longer have 5.2v on the standby windings, so I will have to take a look tomorrow, I don't have any more time tonight. I'll let you know my findings!

Thanks!

[budm]

Re: Samsung LE32R88BD/ BN44-00155A

You need to report what Voltages you have on all 3 legs of the QB802.
"I'm not sure what the ps_on is, is this the on/off pin (pin 3 of Cmn801?)" It sounds like you look at the schematic wrong, pin 3 is STBY 5.2V power supply, Pin 1 is Power ON/OFF (same as PS-ON) it is labeled as PS as printed on the board.
So what ON/OFF pin and the 5V STBY pin did you use on your post #262?

[simmo1337]

Re: Samsung LE32R88BD/ BN44-00155A

Thanks for the speedy reply!

Yes, the standby works and I do get >20v, 26.4v to be precise. I've tested the optocoupler off the board, by applying incremental currents to the led, and measuring the resistors which does decrease, so I think that's okay. But, as you mentioned, I don't get 15v on the emitter of QB802, however, I'm not sure what the ps_on is, is this the on/off pin (pin 3 of Cmn801?)

The zener and diode (zdb805 and db804) seem to be okay with a diode checker, likewise the QB802 is okay, so what could cause the missing 15v?

Once I get this voltage, I'll start looking at the PFC too!

Thanks again!

So the standby power supply section is working, correct?
What Voltage do you have on the cap CB806? There should be >20V on that caps as long as the standby power supply is running, if no Voltage on the cap then check the resistor RB803.
When the PS-ON is present, the Photo Transistor inside the Opto PC801S will be turned on, that will forward bias QB802 which is setup as 15V linear regulator to supply the regukated 15V to run the PFC IC ICP801S.
If you get the PFC to work but still do not have 24V DC or low output on the 24V, then you need to check the capacitance of the DC blocker/Coupling cap CM808.

[budm]

Re: Samsung LE32R88BD/ BN44-00155A

So the standby power supply section is working, correct?
What Voltage do you have on the cap CB806? There should be >20V on that caps as long as the standby power supply is running, if no Voltage on the cap then check the resistor RB803.
When the PS-ON is present, the Photo Transistor inside the Opto PC801S will be turned on, that will forward bias QB802 which is setup as 15V linear regulator to supply the regukated 15V to run the PFC IC ICP801S.
If you get the PFC to work but still do not have 24V DC or low output on the 24V, then you need to check the capacitance of the DC blocker/Coupling cap CM808.

[simmo1337]

Re: Samsung LE32R88BD/ BN44-00155A

Hey guys!

I'm relatively new to bad caps, and to repairing consumer products.

I have the BN44-00155A board, with a blown RM801 resistor. The same story, glue everywhere, which after time.becomes conductive (I saw an EEVblog video a while ago with the same issue). I did find the problem before this forum, but after replacing the resistor with the closest value I had (0.7ohm) I still can't get it to work.

Here's a list of things I've tried, not exhaustive, butthe most relevant:

1) Dm831-835 power diodes have been checked with a meter, seem to be okay.
2) qm801/2 checked with meter, seem to be okay.
3) checked the two fuses, values of the power resistors, and many furnace mount components
3) No AC vtage across the primary of tm801s
4) there's no 24v output, and as you can see by the photos, only 325v on the cap for the booster.

I've been simulating the power on switch with a resistor across the standby voltage pin (which is a steady 5.2v) and the on/off pin. However, I don't see 26v on m_Vcc like I would expect.

My thoughts were that the on/off command turns on the npn, which allows current to flow through the optocoupler, the voltage at point cb806, is then presented on the emitter of qb802?

Could someone explain that section of the circuit to me and help explain why I only have 80mv on m_Vcc? I've tried to remove everything connected to m_Vcc incase it was dragging it down but to no avail!

Also, does it matter that my mains input I'm using for testing doesn't have an earth lead? And does this mean j can hook up a scope without worry of blowing it up?

Thanks,


Simmo.

http://imgur.com/gallery/C5B946W

[jetadm123]

Re: Samsung LE32R88BD/ BN44-00155A

Sounds like the power supply was in continuous use for cctv. Quite possible other caps (specifically the small caps, IE 47uf,etc) might be failing. I would first try heating up the small caps with a hair dryer to see if you can reduce the time for the set to turn on. If this this does not work, try heating various portions of the power supply to see if you accelerate the turn on time and narrow down the area that's causing the problem.

[rgreair]

Re: Samsung LE32R88BD/ BN44-00155A

Hi, i'm new, I have the same board for the 32inch model, had a bad capacitor 10v 1000uf replaced this and would not turn on, i tried the things mentioned in this post,. on its own it will turn on after 15 minutes, resistor in rm801 checks out fine, capacitor cm861 had blown cap. replaced this. 24 volts fluctuating around 12 to 17 volts and slowly goes up to past 24 volts then tv turns on, this is on cm802 (s) any ideas on this. previous own used tv for cctv and was on until a power cut. does work fine after its been trying for 15 minuets.

[pitbull2510]

Re: Samsung LE32R88BD/ BN44-00155A

Hello everyone I have here such a power supply bn44-00155a in which all the voltage pulses pulsate, until it was found that there were swollen electrolytes cm851 and cm852 after the replacement noticed the pulsation sinned on the optocoupler checked all 4 and all 4 working and then replaced the resistor rm801 it also is the fuse including changing cp801 db851 dzm854 qm801 qm802, dm801 dm802 tested a large electrolyte cp803 but it is normal. Stress all normal but throbbing I do not know where to further dig help guys