Polaroid tlu-01541cu s/b light on set dead

[TEDDIBEAR]

Fault on this set was bad caps as usual which were replaced,on switch on no volts, second fault blown AOD403 p channel mosfet when replaced returned 5V rail and standby led, pressing on button returned 12v rail, I still have no backlight or any responce except plop from speakers, I do not know what voltages I should be getting on these connections BRI,B ON,P ON,or SB or their source, I do not think the backlight oscillator circuit is being switched on as no volts on IC pin 12 vcc,
Not having a circuit diagram it is difficult to know where to look, any help would be appreciated, I think this chassis is used in Goodmans,Grundig,Alba,and Bush.
John

[dick_barton]

Re: Polaroid tlu-01541cu s/b light on set dead

Some good clear photo's of your circuit boards is always a good start.

IC Pin 12? Whatis the part number of that IC

[dick_barton]

Re: Polaroid tlu-01541cu s/b light on set dead

Some good clear photo's of your circuit boards is always a good start.

IC Pin 12? What is the part number of that IC

Edit
Sorry for the duplication

[TEDDIBEAR]

Re: Polaroid tlu-01541cu s/b light on set dead

Pictures uploaded screwdriver indicates relevent items.
John

[dick_barton]

Re: Polaroid tlu-01541cu s/b light on set dead

The first check is test what voltages you have at the connector alongside the legend shown in photo 6 of 7

[TEDDIBEAR]

Re: Polaroid tlu-01541cu s/b light on set dead

Voltages are as follows

+5v-+5v =5v
SB -SB = 0v ?
GND-GND = 0V
GND-P/ON = 0V ?
BRI -B/ON = 0V ?
GND-GND = 0V
+12V-12V = 12V
All ? unable to trace source
Thanks
John

[dick_barton]

Re: Polaroid tlu-01541cu s/b light on set dead

There are 14 pins so are these all 14 or just the 1st row of 7.
There should be some voltage readings for SB, B/ON and P/ON
B/ON could be Backlight On
P/ON could be Panel On
SB maybe Standby and you say that pressing On button brings up the 12V supply so it may be that SB is High when the set is in standby and 0V when you come out of standby.

Have you checked the red fuse on the board.

[TEDDIBEAR]

Re: Polaroid tlu-01541cu s/b light on set dead

This is all 14 pins as in picture 6, when mains is applied to power supply panel I only get +5 volt on + 5volt pair when I press sb button on remote I then get +12 volt but nothing on any other of the pins if I then press sb button on remote +12 volt remains until you unplug and start again.
John

[dick_barton]

Re: Polaroid tlu-01541cu s/b light on set dead

There must be some feedback to the power supply to enable the 12V supply to switch on.
Have you measured the voltages on the connected before and after you switch it on via the remote.

[budm]

Re: Polaroid tlu-01541cu s/b light on set dead

You need to recheck Voltage on the power supply connector, seems to me you have measurement error.
https://www.badcaps.net/forum/attach...5&d=1612363588
The power supply board only has one power transformer to supply the needed Voltages, it is an always on power supply, the switched +5V and switched +12V are done through switched MOSFET's. The main power supply is working otherwise you will not have any Voltages on the cold side at all.
If you look at the bottom side of the power supply, you will see that switched MOSFET Q204 (where you screw driver is pointed to) Drain pin is connected to SB pins (Standby 5V/Always on 5V) pin, the +5 pin is connected Source pin of the switched MOSFET Q204 which supplies the +5V, switched MOSFET Q202 is for switched 12V.
Since you do have switched +5V and switched +12V that means P-ON (PS-ON) control Voltage must be present from the main board.
B/ON = BL-ON
BRI = Backlights dimmer control.

BTW, if Q204 was shorted then the switched +5V will always be present. The SB is the always on +5V that is fed to switched MOSFET Q204 for the switched +5V.
Also the red rectangular fuse for the backlights inverter circuit is OK, correct?

[TEDDIBEAR]

Re: Polaroid tlu-01541cu s/b light on set dead

Thank you for your replies.
This is the state of affairs
switch on at main switch I have +5 volts on +5 volt terminal pin, I also have +5 volts on the SB standby terminal, no +12v, when I press Standby button on remote I get +5 volt on P/on terminal pin and then +12v on +12v terminal pin,
I get nothing on B/on or Bri terminals. hope that makes sence, should I only have +5 volt on SB terninal and zero on +5 terminal on switch on and should the +5 volt only appear when Standby button is activated?.
If you then press standby button again board does not go back into standby and all voltages remain.
John

[TEDDIBEAR]

Re: Polaroid tlu-01541cu s/b light on set dead

Bud
After reading your brilliant text on the other thread, I set to work rechecking my work so far I realised I had ordered and fitted the wrong Mosfet looking at the old devise with a microscope as the markings were soo bad the 3 turned out to be a 8, the device I fitted was a AOD403 P fet should have been a AOD408 N fet.fitting a N fet brought the following readings, on switch on, +5 volts on SB terminal, pressing standby button I get +5 volts +12 volts, +3.3 volts on P/ON, +5 BRI, but nothing on B/ON. any ideas?
John

[budm]

Re: Polaroid tlu-01541cu s/b light on set dead

TV unplugged, then check the resistance between Ground and B/ON pin.
The BL-ON is controlled by the main board.

[TEDDIBEAR]

Re: Polaroid tlu-01541cu s/b light on set dead

TV unplugged, then check the resistance between Ground and B/ON pin.
The BL-ON is controlled by the main board.

Have checked resistance between B/ON pin and ground = 10k

BL-ON is fed from transistor Q209 on main board there appears to be no volts on E-B-C of this transistor, the transistor Q208 does have 5 volts on collector nothing on base or emmiter, but with out a circuit diagram it is hard to find where the switching signal is comming from.
If I were to link B/ON to P/ON do you think that would be worth trying?

john

[TEDDIBEAR]

Re: Polaroid tlu-01541cu s/b light on set dead

Have checked resistance between B/ON pin and ground = 10k

BL-ON is fed from transistor Q209 on main board there appears to be no volts on E-B-C of this transistor, the transistor Q208 does have 5 volts on collector nothing on base or emmiter, but with out a circuit diagram it is hard to find where the switching signal is comming from.
If I were to link B/ON to P/ON do you think that would be worth trying?

john

I have gone one step further linked a Ik resistor between B/ON & P/ON still zero volts on B/ON, left resistor in position disconnected B/ON feed from main board now have back light working, so I now have a glowing screen no sound no display so it looks like I have hit the buffers unless you have any suggestions.
John

[nomoresonys]

Re: Polaroid tlu-01541cu s/b light on set dead

Do you have a stand alone tcon board on this tv?

[TEDDIBEAR]

Re: Polaroid tlu-01541cu s/b light on set dead

Do you have a stand alone tcon board on this tv?

The Tcon board is part of the LCD screen, attached with film connections.
John