Samsung BN44-00259A standby question

[Crystaleyes]

Hi all.

I started a thread while back regarding TV power supply standby circuitry as it is something I am not quite on top of.
SMPS theory and function is becoming more familiar, however the standby part is still a bit of a mystery.

Anyway, a friend has this TV with the above mentioned power supply board which has no standby voltage, nor any other voltages leaving the board.
The mains AC comes in fine, gets filtered and rectified with power is on the main filter cap as well as the transformer and drain pins of the ICE3B0665J, but that's it.

Looking at the schematic doesn't really enlighten the situation for me and nothing appears severely damaged with a visual inspection, although ZM801 no longer has any markings, and the ICE3B0665J does appear to have a scorch marking on the board beneath it. For some reason the iode measures as a semi-conductor, but not as a zener when using the component tester.

This is all perhaps secondary as I would first love to understand the circuitry of this particular standby. I suspect the ICE chip is involved but I'm not seeing how? I had been under the impression that the standby circuits had their own little transformers, but clearly this is not always the case.

What am I missing?


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[R_J]

Re: Samsung BN44-00259A standby question

What voltage do you have on pin7 (vcc) of UM801s? It may be as simple as CM804 and CM808 bad (low capacity) or the ic itself may be bad.

[CapLeaker]

Re: Samsung BN44-00259A standby question

I can see a bad capacitor next to the ICE chip very close to the heat sink.

[redwire]

Re: Samsung BN44-00259A standby question

I would say the chip is blown from the soot marks, and so check the fusible resistor RM869 0.4Ω nearby and the electrolytic capacitors around it. CM804 47uF 50V, CM808 22uF 50V are critical for the IC. The 10V zener ZM801 still has a faint stripe.
This board is dated 2009 or 14 years old... I had one PSU with leaking yellow goo primary cap CP815 that went high value. I would check/replace all the electrolytics, I would say they are end of life due to the heat.

[Crystaleyes]

Re: Samsung BN44-00259A standby question

What voltage do you have on pin7 (vcc) of UM801s? It may be as simple as CM804 and CM808 bad (low capacity) or the ic itself may be bad.

Hi fella.

0.000v on the Vcc

[R_J]

Re: Samsung BN44-00259A standby question

Likely the ic is bad, the internal startup cell should provide some startup voltage on the vcc line, It is possible there is a shorted component on the vcc line but I suspect the ic is kaput, Replace those small electrolitics as well, they are likely bad.

[Crystaleyes]

Re: Samsung BN44-00259A standby question

I can see a bad capacitor next to the ICE chip very close to the heat sink.

If you mean the electrolytic, then that is still good.

[Crystaleyes]

Re: Samsung BN44-00259A standby question

I would say the chip is blown from the soot marks, and so check the fusible resistor RM869 0.4Ω nearby and the electrolytic capacitors around it. CM804 47uF 50V, CM808 22uF 50V are critical for the IC. The 10V zener ZM801 still has a faint stripe.
This board is dated 2009 or 14 years old... I had one PSU with leaking yellow goo primary cap CP815 that went high value. I would check/replace all the electrolytics, I would say they are end of life due to the heat.

The 0.4Ω resistor is now just over 0.8Ω so I'll change that but all the caps I've tested (so far) have come up fine.
For some reason ZM801 only registers as a standard diode and not a zener so I'll change that too.

It's not a bad idea to change all the caps whilst replacing that ICE chip, so let's see?

As for standby circuit theory, this ICE chip is where the +5v standby is controlled?
The rectified input passes through the primary of transformer TM801S and generates 5v which is switched through this ICE chip... Is that correct?

If I'm ever gonna become proficient at SMPS repairs in general, then I need to get a grasp of each section of the circuitry, eh?

[Crystaleyes]

Re: Samsung BN44-00259A standby question

Couldn't find an ICE3BR0665J in the local shops but did find an ICE3B0365J.

The only obvious difference I'm seeing in the datasheets, is that one has a 'BA' on pin 1 and one has 'SoftS' on pin 1.

I figured that the 365 might serve to at least verify if the 5v standby can be seen?
If so then I can buy the 665 online

Anyone know if this will work before I do it?

Datasheets below...


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[CapLeaker]

Re: Samsung BN44-00259A standby question

You have there 2 power supplies. One is always on and that is the ICE chip. No you cant sub a different chip with a different pin configuration. If you have no Vcc on the ICE chip, it can't run. Something must be open or a dead short to GND. Follow the line backwards. Oh, forgot to mention that cap... id still change it. It's close to the heat sink and the sleeve has shrunken a bit. Any cap near a heat source spells trouble at some point.

[Crystaleyes]

Re: Samsung BN44-00259A standby question

You have there 2 power supplies. One is always on and that is the ICE chip. No you cant sub a different chip with a different pin configuration. If you have no Vcc on the ICE chip, it can't run. Something must be open or a dead short to GND. Follow the line backwards. Oh, forgot to mention that cap... id still change it. It's close to the heat sink and the sleeve has shrunken a bit. Any cap near a heat source spells trouble at some point.

Thanks.

Please correct me if I am mistaken, however with what I can understand from the schematic is that the ICE Vcc comes from terminals 5 & 6 on the transformer TM801S, and passes through RM805, DM803, DM802 and RM890.
None of these are open, nor is there any potential across terminals 5 & 6.

This is why I need to learn about standby circuitry.

Perhaps I should be asking, "where does the 5v come from?" - as I don't see any 7805 or similar regulator...

[R_J]

Re: Samsung BN44-00259A standby question

The ICE3BR0665J provides the start vcc as stated in the datasheet (read page 7), the transformer provides the sustain voltage to keep the ic operating.

[CapLeaker]

Re: Samsung BN44-00259A standby question

The ICE (there are also others like TOP,TNY etc) is on the primary. So when conditions are met, it will start switching on the primary side of the transformer, the secondary picks it up as a lower voltage, sends it through a diode(s) DM851, inductor capacitor and voila there is your standby voltage, which is always on.
In order to prevent damage, the IC incorporates things like high temp shut off, under voltage lockout, current sensing, over voltage, etc.
All in a nutshell, always go for the low hanging fruit like is there Vcc on the chip, is there a short on the secondary, write down the voltages on each pin of the IC and read the data sheet thoroughly. The data sheet will tell you exactly what voltage ranges to expect on what pin. Also read on how the protection works and sometimes you get even example circuits, which is a big help if you don’t have a schematic for whatever electronic board you are trying to fix.
If it helps, maybe read the schematic backwards, find what you want like stby and trace it back.
The other power supply (PFC) only turns on if you tell it to be on.

[Crystaleyes]

Re: Samsung BN44-00259A standby question

Hi all.
Apologies for the delayed response, but I feel quite embarrassed that I opened this thread as the owner of the TV decided that I was asking too much to fix it (40 USD for a replacement PS board) and asked me to return the TV so he could take it elsewhere.

I had been asking here about fixing it, purely to expand my understanding of switched moded PSU's in TV's but clearly thsi time round it was not meant to happen.

Didn't mean to waste anyones time but thanks for all the input.

[R_J]

Re: Samsung BN44-00259A standby question

This is why I charge an estimate fee up front of at least $40.00, that way I get paid for my time. If they don't want to pay it, I don't bother looking at it.

[Crystaleyes]

Re: Samsung BN44-00259A standby question

This is why I charge an estimate fee up front of at least $40.00, that way I get paid for my time. If they don't want to pay it, I don't bother looking at it.

Not actually 'working' as a repair tech, I hadn't given this much thought, however I actually went to some effort to first test the TV to identify where the problem lay, and then to source a replacement PSU board for a reasonable price.
Several (if not many) hours were given to this, as well as buying all the electrolytic caps and ICE IC, only to be told that my services weren't required.

So I can see myself charging for diagnosing in the near future...

[nomoresonys]

Re: Samsung BN44-00259A standby question

If that was a friend, I would hate to meet your enemies.