Samsung QN75Q60TAF Boot Loop fixed but no picture

[howardc64]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Yes, that's right, the lower the voltage, the greater the current and, accordingly, the lower the resistance. And can you post a photo of a DC / DC converter in a QFN package, maybe I can find what kind of chip it is.

Mine is just 20pin QFN with "AWRCDE" marking.

More interesting to this thread is OP's DC/DC in post #20. Looks like N12R. Google also didn't find anything.

But probably just for curiosity as OPs circuit seems to be working fine and mine seem stuck on dead eMMC in another thread haha.

[lotas]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

I actually reached similar understanding on my main board. A lot of 200ohm caps on the 2x 1V rail to the SOC. All short beeped on my old Fluke 27 DMM in diode mode.

My background is not Electrical Engineering (can't even do ohms law well haha) but I thought the following

- If a logic processor has to switch at 1GHz, there can't be high resistance between the + and GND high frequency logic rails. Otherwise, need higher voltage and produce a lot more heat to switch at that speed.

So OP's 12ohm diode beeps are probably on SOC's core logic supply lines as you said. On my board, the 4A 1V line had a 20pin QFN voltage supply chip with markings that google can'f find a source or datasheet. Right next to a big inductor, large + and GND planes to the SOC with lots of low resistance caps. Looks like OP's circuit in this area.

Yes, that's right, the lower the voltage, the greater the current and, accordingly, the lower the resistance. And can you post a photo of a DC / DC converter in a QFN package, maybe I can find what kind of chip it is.

[howardc64]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

There are supply lines on the motherboard, this is the power supply for the processor core and the video core, and on these lines the supply voltage is low, about 1v, but the current is a few amperes, and these lines already have a low resistance of 20, 15, 10 Om, maybe less and they cost on this line a lot of ceramic capacitors, and when measured with a multimeter, it will beep and show low resistance.

I actually reached similar understanding on my main board. A lot of 200ohm caps on the 2x 1V rail to the SOC. All short beeped on my old Fluke 27 DMM in diode mode.

My background is not Electrical Engineering (can't even do ohms law well haha) but I thought the following

- If a logic processor has to switch at 1GHz, there can't be high resistance between the + and GND high frequency logic rails. Otherwise, need higher voltage and produce a lot more heat to switch at that speed.

So OP's 12ohm diode beeps are probably on SOC's core logic supply lines as you said. On my board, the 4A 1V line had a 20pin QFN voltage supply chip with markings that google can'f find a source or datasheet. Right next to a big inductor, large + and GND planes to the SOC with lots of low resistance caps. Looks like OP's circuit in this area.

[nomoresonys]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Every one that I have tested, only beeped on one side when tested from ground, unless it was bad, even with .01 resistance no beep at that resistance and beep on other side which is grounded.

[lotas]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Ok, how bout you test those caps properly, if your meter beeps on diode mode, put the neg probe on a ground one of the copper holes where the screws go is fine, pos. probe on each side of cap, should beep on one side not the other, or use ohm mode, should get reading on one side and very close to 0 ohms on the other.

There are supply lines on the motherboard, this is the power supply for the processor core and the video core, and on these lines the supply voltage is low, about 1v, but the current is a few amperes, and these lines already have a low resistance of 20, 15, 10 Om, maybe less and they cost on this line a lot of ceramic capacitors, and when measured with a multimeter, it will beep and show low resistance.

[nomoresonys]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Ok, how bout you test those caps properly, if your meter beeps on diode mode, put the neg probe on a ground one of the copper holes where the screws go is fine, pos. probe on each side of cap, should beep on one side not the other, or use ohm mode, should get reading on one side and very close to 0 ohms on the other.

[howardc64]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

OP Post #20 for me are wrong measurements

this why i asked him at post#33 and his answer at post #36 was the proof of his wrong measurements.

or did i missed some points regards my poor English LOL

The main board appears good given the tests performed so far (post #1 has sound+IR, only necessary to mask 2 pins on LCD panel connector) Was just curious what is the voltage rail with 12ohm caps near inductor.

[Diah]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Cuz he gots dem shorts over there on de MB, post 20.

OP Post #20 for me are wrong measurements

this why i asked him at post#33 and his answer at post #36 was the proof of his wrong measurements.

or did i missed some points regards my poor English LOL

[nomoresonys]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Cuz he gots dem shorts over there on de MB, post 20.

[Diah]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Of course none of that will make the tv work, as long as the mainboard is shorted.

where are the short on MB !!! the posts are so many and the required test not enough for me..????
however i just understand from OP first post he mask 35&36 and tv boot normal and can hear music and BL come on but Panel black.. and i did explain why its black because he turn off the panel by masking VDD !!!

so why we do need to consider back on MB if the TV booting, BL OK,and Sound OK !!!

[howardc64]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

@howardc64, the 12 ohms was measured on the main board, i believe you mentioned R89 earlier being an inductor. It was all caps around that.

What is the chip # to the right of the R82 inductor? N?12R 5334E? Looks like its the chip that generates the voltage that flows through the inductor and all the nearby caps connects the voltage plane to ground (also connected to the chip) for smoothing our noises. Not sure its related to the audio chip below.

Would be good to know what the chip is and whether 12ohm between power and ground should be expected.

[nomoresonys]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Of course none of that will make the tv work, as long as the mainboard is shorted.

[lotas]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

That 8 pin IC is not easy to remove. Low melt solder is probably best solution. Hot air station can do damage in that small buffer board area if not reasonably experienced.

There is a thin board, with the help of tweezers and a regular soldering iron + flux, you can easily remove it.

[nomoresonys]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

One thing is pretty simple, IF you have those caps on the mainboard reading short with everything else dis-connected from mainboard, then the short IS on the mainboard and needs to be fixed or a new mainboard.

[howardc64]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

It will be tomorrow, i don't have the tools to remove an IC right now.

That 8 pin IC is not easy to remove. Low melt solder is probably best solution. Hot air station can do damage in that small buffer board area if not reasonably experienced.

[Diah]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

ok

after this.. if there boot loop again / no start... then need to remove the ESD DT 601 & DT 602 and check again to start Tv with out mask

[Nicktronic]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

It will be tomorrow, i don't have the tools to remove an IC right now.

[Nicktronic]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

ok

[Diah]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Sorry I don't know if i understand..... So, take the masking off, turn on tv. Measure 36 and 35 on buffer board as marked in picture?

After, remove SPI IC601?....Test again?

no need to measure at all. just remove the spi and the mask then turn on

[Nicktronic]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Sorry I don't know if i understand..... So, take the masking off, turn on tv. Measure 36 and 35 on buffer board as marked in picture?

After, remove SPI IC601?....Test again?