Toshiba 58L4300UC Dim picture

[Mayn]

Re: Toshiba 58L4300UC Dim picture

LB1-5 + All 117V
LB1-4 - All 5.9-6V
LB5- is showing 0V

All LED strips appear to be on though. If I bring up the menu the brightness is consistent with no dark spots.

[budm]

Re: Toshiba 58L4300UC Dim picture

The LB1-5 show the same DCV because they are the Anodes of all 5 LED string which are connected to the same power supply.
The LB1-5 - are the Cathode return of each LED string, and each one of the return is connected to those 5 MOSFETs (Q902A~E (SMD), Q907A~E) and they are connected to the current sensing resistors (R908A-E, R910A-E (resistors are connected in parallel) and then to GND return. U901 is the LED controller IC.
So there is problem with LB5-, to me that is an open circuit in that LED string that is why you are getting 0V, or the LB5- is grounded due to fault in the return line, so check the resistance between GND and LB5- to see what you get.

Pictures provided by SHOPJIMMY.

[Mayn]

Re: Toshiba 58L4300UC Dim picture

I get an open circuit between LB5- and ground

[budm]

Re: Toshiba 58L4300UC Dim picture

I get an open circuit between LB5- and ground

OK, it is not shorted to GND, so the only thing left will be that LB5 string has open circuit.
You can try swapping LB5- wire with other LB- to see if the problem will follow.

[Mayn]

Re: Toshiba 58L4300UC Dim picture

yup, the problem follows. wherever I put the wire that's the original LB5- I get 0V.

So i have a bad led, correct?

[Mayn]

Re: Toshiba 58L4300UC Dim picture

Got it apart. The top row of LED's aren't powering on. Going to see if I can determine which one/ones are the problem.
I have the LED strips out of a 50" Toshiba, and they look to be the same LED's, so if I can figure out which one/ones are the problem I should have spares.

[Mayn]

Re: Toshiba 58L4300UC Dim picture

Before doing anything I swapped the power going to the top 2 rows of led's, just to confirm it wasn't something else.
The original power going to the dead led strip powered up the other row, so that was good.
With the other power connected, I got the top row of led's to blink on and off.
When I pulled the strip, the connector between the two strips fell off. I'm in the process of resoldering this now.

Hoping that was the problem all along.

[Mayn]

Re: Toshiba 58L4300UC Dim picture

Fixed the connector between the led strips. still have the dim picture though. I did notice a slight buzz coming from one of the transformers on the psu. Considering just testing every component on the board lol.

Any idea what actually delivers the voltage to control the brightness of the picture?

[Mayn]

Re: Toshiba 58L4300UC Dim picture

So, finally got a chance to get back to this tv.

Backlights all have 115V across them, but still have no ability to adjust the brightness of the image, it just stays dim.

If I go into the menu and adjust the mode from standard to movie etc... when I make a selection the brightness does jump up for a split second before settling back to being dim.

Any ideas?

[Mayn]

Re: Toshiba 58L4300UC Dim picture

Backlights all just kind of glow, not nearly as bright as they should be. Even with the resistor between PWM and 5v there is no change.

[Mayn]

Re: Toshiba 58L4300UC Dim picture

Could a bad t-con board cause a dim picture? Almost worth the risk lol

[dick_barton]

Re: Toshiba 58L4300UC Dim picture

So, finally got a chance to get back to this tv.

Backlights all have 115V across them, but still have no ability to adjust the brightness of the image, it just stays dim.

If I go into the menu and adjust the mode from standard to movie etc... when I make a selection the brightness does jump up for a split second before settling back to being dim.

Any ideas?

On another thread they say that 135V brought all the leds on so could explain why they are dim.

https://www.badcaps.net/forum/showthread.php?t=55206

[Mayn]

Re: Toshiba 58L4300UC Dim picture

That's probably the issue. The trick is, what's causing it lol

[dick_barton]

Re: Toshiba 58L4300UC Dim picture

That will be the led booster circuit which I believe from reading that thread was an OZ9908B and if so you need to investigate that circuit. It could be that it's not boosting or the input supply it's boosting is low.

[dick_barton]

Re: Toshiba 58L4300UC Dim picture

You give in post#12 the panel number. The data sheet says it should be typical 148V per string. There are 5 strings of 23 leds per string, so 6V leds. So your led driving voltage is way too low.
See section 3.2.1.

Edit
You could sell the replacement mainboard you purchased (as in your other thread) since it is doubtful the original was faulty and put it towards a replacement power supply.

[Mayn]

Re: Toshiba 58L4300UC Dim picture

any idea what voltages I should be seeing from O9908B? Or where else should I be looking?

Also, I almost looks like this ic got hot. Looking at the solder points on it, it just doesn't look as slick and clean as the other chips soldered to this board.

Think I could just replace it and hope for the best?

[Mayn]

Re: Toshiba 58L4300UC Dim picture

I keep coming back to this tv. Only power supply I can find is on Ebay and it's quite pricey. If I knew 100% this was the problem I'd get it, but if it's just an ic i'll change that first and try it. Anyone got a schematic for the power supply PK101W0220I ?

[dskall]

Re: Toshiba 58L4300UC Dim picture

Where you having the dim leds before you repaired led strip?

[dick_barton]

Re: Toshiba 58L4300UC Dim picture

I believe that you have the wrong power supply board and that was probably changed and not the main board.

The 58L4300UC part number for the power supply is PK101W0230I


Edit
Toshiba 58L1350U Power Supply LED Board PK101W0220I

[dick_barton]

Re: Toshiba 58L4300UC Dim picture

Looking at shopjimmy it appears as though the PK101W0220I is used for the 58L1350U only and that the PK101W0230I can be used in the 58L1350U and 58L4300U.

If anyone could verify and know the reason why it would be interesting.