Samsung UH50EH5300FXZA, help with a transformer?

[howardc64]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Repaired the PSU and saved one of these from the dumps. PSU PN BN44-00668A. Got it for free after power outage took it out.

CP805 (221pf 1kv) blew up with all the smoke exiting towards bridge rectifier and under the heat sink. Tested all MOSFETs and big diodes per budm in post #2. QP801CS was shorted. Fuse was blown of course. TV came up after replacing these 3 components.

Pic attached, you can still see the smoked debris field near the bridge rectifier haha. Thanks for badcaps again on this one, no exact schematics online but many similar BN PSU schematic does exist.

Avoiding software update per OP's post in #77. Had a similar experience with a 32" Samsung that screwed its firmware (was able to reload when cold and recover in that case)

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Thank you budm for all of your help, I appreciate it!

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

This will be my final update on this TV. It continued to work fine with no other problems so it is approved and now gone. I donated it to an animal rescue organization for their waiting room, so they can put up slide shows and show people what they do!

Thank you to everyone who participated in this thread and I do appreciate it!

Thank you for supporting animal rescue organization.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

This will be my final update on this TV. It continued to work fine with no other problems so it is approved and now gone. I donated it to an animal rescue organization for their waiting room, so they can put up slide shows and show people what they do!

Thank you to everyone who participated in this thread and I do appreciate it!

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Well the replacement main board arrived. I installed it in to the TV and so far we're back in business!

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

It uses constant current driving circuit, not just simple current limiting resistor.
The D- is the Cathode return of the LED string that goes to ground via PWM control MOSFET Q9151C and current sensing resistors.

Just for the heck of it I checked for voltage at the EEPROM test points and found they all have 3.29v. Does this mean the EEPROM isn't working or shorted maybe?

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

229V backlight voltage spec is confirmed written on my board. In this case I agree the reading is high. I don't see any current limiting resistors on the top of the board so they must be SMD on the back. Seems like I ought to check them if so equipped?

It uses constant current driving circuit, not just simple current limiting resistor.
The D- is the Cathode return of the LED string that goes to ground via PWM control MOSFET Q9151C and current sensing resistors.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

'12 A5V.......5.25 constant'
Since standby is contstant but the control signals are not then you have problem some where on the main board, exactly what I do not know.

I do believe the main board is the problem as well.

The problem started while smart hub was updating. Seemed OK until then save for an extended turn-on time.

Reminds me of what this TV is doing, another one of mine.

https://www.badcaps.net/forum/showth...un46eh6030fxza

It also had a flashing standby light when TV is turned on but no backlights or display. I heated up one of the RAM chips and it would turn on. I also applied heat to the same RAM chip on this 50" and it seemed to help it turn on.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

OK self test is fine then if it stays as long as the AC is applied to the TV.
But the 264V on the Anode of the first string is quite high unless the Voltage chart is wrong.

229V backlight voltage spec is confirmed written on my board. In this case I agree the reading is high. I don't see any current limiting resistors on the top of the board so they must be SMD on the back. Seems like I ought to check them if so equipped?

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

'12 A5V.......5.25 constant'
Since standby is contstant but the control signals are not then you have problem some where on the main board, exactly what I do not know.

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

When I unhook the main board from the PSU the backlights are on.

OK self test is fine then if it stays as long as the AC is applied to the TV.
But the 264V on the Anode of the first string is quite high unless the Voltage chart is wrong.

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

How many wires are there on the LED connector?

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

1) What is the P/N of LED driver IC9151 8-pin SMD?
2) Lift up one leg of diode D8151C and check the RESISTANCE betweent he two legs in both directions.

"EDIT/ADD: I unhooked the main board from the PSU and took voltage readings on the backlight connector:" So the backlights are still not on?
If you look at the LED Voltage chart, it shows 229v @ 470mA with load, you are getting 264V so it means it is not seeing the full load.

When I unhook the main board from the PSU the backlights are on, this post was updated 5min ago

EDIT/ADD: I unhooked the main board from the PSU and took voltage readings on the backlight connector:

1 NC
2 D+.........264
3 S1- ........159
4 S2+ .......159
5 NC
6 S2- ........107
7 S3+........107
8 D- ..........55
9 NC

Voltage difference between D+ and S1- = 104v
Voltage difference between S2+ and S2- = 52v
Voltage difference between S3+ and D- = 52v
D+ and S1- run two pair of strings. 104/2 = 52

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

1) What is the P/N of LED driver IC9151 8-pin SMD?
2) Lift up one leg of diode D8151C and check the RESISTANCE betweent he two legs in both directions.

"EDIT/ADD: I unhooked the main board from the PSU and took voltage readings on the backlight connector:" So the backlights are still not on?
If you look at the LED Voltage chart, it shows 229v @ 470mA with load, you are getting 264V so it means it is not seeing the full load.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Updated voltage readings:

1 B13V.......12.47v, drops to 0 and comes back up to 12.47v
2 P_dim......2.0v when backlights are on, otherwise 0-.7v when boot looping
3 B13V.......Same as 1
4 B13V.......Same as 1
5 Vamp......12.47v drops to 0 and comes back up to 12.47v
6 BLU_on....4.79v when backlights are on, otherwise 0-..13v when boot looping
7 Vamp......12.47v
8, 9, 10......GND
11 B5V.......5.24v drops to 0 and comes back up to 5.24
12 A5V.......5.25 constant
13 B5V.......Same as 11
14 PS_on....3.29v, drops to .2v, comes back up to 3.29v

Furthermore I took voltage readings at the backlight connector, attached and unhooked from the PSU:

1 NC
2 D+..........347v, drops to 220v, returns to 347v......unhooked 347v
3 S1- .........297v, drops to 176v, returns to 297v......unhooked 0v
4 S2+ ........297v, drops to 176v, returns to 297v......unhooked 0v
5 NC
6 S2- .........306v, drops to 176v, returns to 306v......unhooked 0v
7 S3+.........306v, drops to 176v, returns to 306v......unhooked 0v
8 D- ...........316v, drops to 208v, returns to 316v.....unhooked 316v
9 NC

EDIT/ADD: I unhooked the main board from the PSU and took voltage readings on the backlight connector:

1 NC
2 D+.........264
3 S1- ........159
4 S2+ .......159
5 NC
6 S2- ........107
7 S3+........107
8 D- ..........55
9 NC

Voltage difference between D+ and S1- = 104v
Voltage difference between S2+ and S2- = 52v
Voltage difference between S3+ and D- = 52v
D+ and S1- run two pair of strings. 104/2 = 52

Based on the voltages found the power supply and backlight strings cannot be the problem, leaving the main, T-CON and connections/panel responsible.

So it looks like all the necessary voltages are available when the main board asks for them, but some of the time the main board isn't sending some command voltages back to the PSU?

The paragraph that was here is redacted

[DXseekerMO]

Update:

I would suspect bad ic, a shorted mos fet would likely blow something, but check the parts in the gate circuit, there might be a zener to ground that is shorted
Taking an ic from another board should be fine

+1

Well today the replacement PSU came in. Seller claimed it was from a new cracked screen TV and worked. When I got it the ground pads were nice and clean so I believe the sellers claim. I put it in the TV and no happy, TV dead. I checked the main cap voltage and found nothing. A further look and the reason showed up....the main fuse was cut out and missing.

Fast forward an hour: Ebay seller refunded my money with no messages, just a refund. I checked for a short in the mains on the board and found nothing, then checked all the FETs and Diodes, all indicated good. I installed the fuse from my old PSU, installed the PSU in the TV.....then lo and behold, the TV turned on and everything worked!

Fast forward another 30min. Everything was looking good, TV channels tuned and functions appeared to be working. I was using smart hub and tried getting in to the youtube app but it said it failed to connect due to network interference then later said it needed updating. I tried to use apps during this time but the little spinning circle with "updating" next to it wouldn't let me. Next thing I know the TV shuts off then starts boot-looping, eventually with no backlights or logo.

I'm letting it cool off to see if it will later turn on and stay on. At that point I intend to re-set smart hub then do a master reset on the TV and try again. So either I interrupted the update and bricked the TV....or perhaps we have an EEPROM or BGA soldering failure.

The good news: The display panel is very good in this TV, no lines or other things I feared fixing a model known for panel issues. I just have the boot loop and that appears to be it.

If it continues to boot loop, aren't there test points near the main EEPROM that can be shorted to re-set the EEPROM itself?

EDIT:ADD: Tried unhooking the power button and WIFI module right after turning it on and the problem still exist.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

I would suspect bad ic, a shorted mos fet would likely blow something, but check the parts in the gate circuit, there might be a zener to ground that is shorted
Taking an ic from another board should be fine

+1

Well sodded dog, I ripped several traces on the board right by that IC. The zener in-circuit did not show short...kind of a moot point now tho.

This is because I still don't have a hot air station. Speaking of, does anyone have an opinion about this one?

https://www.ebay.com/itm/X-Tronic-Mo...MAi:rk:17:pf:0

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

I would suspect bad ic, a shorted mos fet would likely blow something, but check the parts in the gate circuit, there might be a zener to ground that is shorted
Taking an ic from another board should be fine

+1

Thanks R_J and budm, I will re-check the gate-related items off that FET and if all is good I will install the IC and report when finished.

Is this IC glued to the board? Any suggestions to deal with that if it is?

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

i would suspect bad ic, a shorted mos fet would likely blow something, but check the parts in the gate circuit, there might be a zener to ground that is shorted
taking an ic from another board should be fine

+1

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

I would suspect bad ic, a shorted mos fet would likely blow something, but check the parts in the gate circuit, there might be a zener to ground that is shorted
Taking an ic from another board should be fine