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**hfosteriii** · 03-10-2017, 10:06 PM

Re: Toshiba 50L1350U only some leds out?

Here are the pics I promised. Hope they are correct. Should be high resolution. Let me know.

Attached Files

**hfosteriii** · 03-10-2017, 10:16 PM

Re: Toshiba 50L1350U only some leds out?

Just looked at the led distribution board. Doesn't appear as though anything could go wrong. No components. No scratches in the circuit or breaks. If need be I'll test.
Thanks again.

**budm** · 03-10-2017, 10:30 PM

Re: Toshiba 50L1350U only some leds out?

You have two set of LED driver circuits, thus two boost converter circuits (QL11, QL12, LL1, LL2, DL1, DL2)
So the question is what DCV do you have on each pin of that 4-pin connector for the LEDs.
You will have to put black probe on the chassis, red probe on one pin at a time on the LED connector and then turn the TV on and see how high the Voltage goes up to and what it settles down to after 3~$ seconds. Turn off the TV and repeat the same on the other 3 pins.
I just saw your chart, from your chart it looks like the problem is in L2 string, you anode (L+) Voltage but no Cathode (L-) return Voltage. QL1, QL5 are PWM Controlled MOSFETs (for maintaining constant current through the LED strings) driven by the LED driver/boost converter SMD IC on the bottom side of the board.
Are you sure you do not have open circuit on the L2 string that is why it went up to 130V before the protection circuit kicks in and drop the Voltage down to 80V, check the inter connector between the LED board really well.
BTW, the LED Voltage (loaded) is 111V as printed on the board.

**jasonbay13** · 03-10-2017, 10:31 PM

Re: Toshiba 50L1350U only some leds out?

do l1 and l2 simply go to the led strips? on your notes you show voltage at both l1 and l2.
what would happen if you swapped the l1 and l2 pins, would the others come on or no change?

"Tested the small smt mosfets"
are you referring to ql1 and ql5, almost looks like the bottom one could be a little melty, but probably just the pic.

**hfosteriii** · 03-10-2017, 11:00 PM

Re: Toshiba 50L1350U only some leds out?

Budm
"Are you sure you do not have open circuit on the L2 string that is why it went up to 130V before the protection circuit kicks in and drop the Voltage down to 80V, check the inter connector between the LED board really well.
BTW, the LED Voltage (loaded) is 111V as printed on the board."

I'll check.

Jasonbay13
I'll swap l1 and two with some jumpers. Yes, mosfets ql1 and ql5. They both tested almost identical. I was concerned as the voltage kept creeping up. Forward voltage I think it was. Might be because my meter puts out 2.5 or 3 plus volts in diode mode? Over the forward voltage threshold of those? Activating the mosfets on the meter check without the gate voltage bring applied?

Any thoughts on the strange voltages at the drains of ql11 and ql12? My thought was because of a open circuit either in cable, connector, circuit or component causing a reverse build up?
BTW, I don't know if I mentioned in my post that I swapped those mosfets and got same readings and results. It's in my note I'm sure but to bring it to attention.
Thanks for the quick replies.

**budm** · 03-10-2017, 11:14 PM

Re: Toshiba 50L1350U only some leds out?

You have no load on L2 connection, either the LED/s are open circuit or the poor solder joints on the SMD connectors on the LED boards.

**hfosteriii** · 03-11-2017, 12:26 AM

Re: Toshiba 50L1350U only some leds out?

When I switch the led strips to a working leg, they all work.
LED board continuity tests good.
Cable and both connectors are continuous.

**hfosteriii** · 03-11-2017, 12:34 AM

Re: Toshiba 50L1350U only some leds out?

I'll run jumpers to swap legs and retest components tomorrow. I did run some continuity tests in diode mode, while powered, and got some strange readings. L2- doesn't test continous or do anything with leads in either direction, but the others do something one way, different things in the opposite. I'll post results of that tomorrow.
It's starting to look like there's opened and closed gates in the OB3372KP, causing a short or open circuit respectively. Possible?

**hfosteriii** · 03-11-2017, 01:03 AM

Re: Toshiba 50L1350U only some leds out?

Budm
" poor solder joints on the SMD connectors on the LED boards."

Do you mean somewhere in the led drive circuit on the power supply board?

Is it possible it's a shorted or blown resistor or cap in the smd section? Or the ic itself?

**budm** · 03-11-2017, 01:34 AM

Re: Toshiba 50L1350U only some leds out?

OK, using logic here:
First: you are getting the Boosted Voltage to feed the L2 LED string so that section is working. If the booster is not working then you will not have that 130V.
Second: You have 130V feeding the Anode of the LED string Anode (+L2) of the LED string but you are not getting anything (0.3V!!) coming out on the Cathode end (L2) of the LED string L1 like what you are getting on the -L1.
So does that make sense to you now?
The LED strip has SMD connector to link the strip together don't they?
Remove the LED connector from the power supply board and check the +L1 and +L2 DCV to see if when you get when you first turn on the TV.
We at badcaps will not be surprised if you find Bad LEDs.

**hfosteriii** · 03-11-2017, 02:32 AM

Re: Toshiba 50L1350U only some leds out?

I'm sorry budm, but I took the led strips from 2, 3, and 4 (L2 leg),and switched them with the strips from 1, 5, and 6. I think I did use logic, in so far that the LEDs 2, 3, and 4 worked on L1's leg and the ones from 1,5,and 6 from leg L1 (that were lit) didn't work on leg L2. So that eliminates that. If they pull a load on leg L1 they certainly don't stop by switching them to leg two. Then I switched them back. All times L2 didn't work regardless of which led sets were installed, yet every time L1 did. The problem isn't the leds sir.
Sorry for any confusion.

**hfosteriii** · 03-11-2017, 02:34 AM

Re: Toshiba 50L1350U only some leds out?

Btw, the voltages remain in the same state also.

**budm** · 03-11-2017, 05:30 PM

Re: Toshiba 50L1350U only some leds out?

What DCV do you get at +L1 and +L2 when the LED connector is not in place? 130V or so?
As I indicate, you have 130V going to +L2 which is the Anode of the first string of the LED, -L2 is the Cathode return, so you should have Voltage on that -L2, you only have 0.3V so compare that to -L1 then you will see that you have open circuit some where.
See example of typical LED setup with two strings of LEDs. You have Voltage on one end and nothing on the other end, something is not completing the circuit.

Attached Files

**hfosteriii** · 03-11-2017, 05:53 PM

Re: Toshiba 50L1350U only some leds out?

First, I want to offer budm my formal apology. It seems I was working of of incorrect information when speaking on the leds. I was assured that they were all switcher out, but after thinking about it last night I had to ask my son, 16, if he actually did. He said he thought so. I checked and sure enough one strip set on each leg was not changed. So I retract my previous statement on that.
Second, I went ahead and changed them all myself this time, and I do indeed have some leds out. One whole r1 strip was out, and the last led on an r2 strip plus the very next led starting the connected l2 strip.
It seems my son changed out some of the working strips on L1. Good teaching moment for him about meticulous work and accuracy, and a lesson for me to trust but VERIFY, especially when dealing with someone still learning.
Again my apologies, as budm was correct in his instincts. I was lax in verifying the information. The fault of course is mine as the teacher, none lies with my son. Only presented as an explanation, not an excuse.

I will test those connections and report the findings.
Sincerely,
Harry

**hfosteriii** · 03-11-2017, 05:55 PM

Re: Toshiba 50L1350U only some leds out?

I did understand your reasoning, budm, but I was (mistakenly) sure that we tested that course of action.
Cheers

**hfosteriii** · 03-11-2017, 05:57 PM

Re: Toshiba 50L1350U only some leds out?

Question, is the forward voltage of the individual leds standard? I didn't know if smt Leda are the same as encapsulated leds. 3.2 volts or so each?

**budm** · 03-11-2017, 05:59 PM

Re: Toshiba 50L1350U only some leds out?

No problem, when the reports defy the logic then something needs to be rechecked.

**budm** · 03-11-2017, 06:11 PM

Re: Toshiba 50L1350U only some leds out?

Originally posted by hfosteriii View Post

Question, is the cigars voltage of the individual leds standard? I didn't know if smt Leda are the same as encapsulated leds. 3.2 volts or so each?

I do not understand what the 'CIGARS' Voltage is.
Those LEDs are rated at 1W.
The popular one that I use is LG LATWT470RELZK (Anode is the large pad)
https://www.badcaps.net/forum/showth...hlight=latw%2A
https://www.badcaps.net/forum/showthread.php?t=51251
I get them from ALIEXPRESS.

**budm** · 03-11-2017, 06:14 PM

Re: Toshiba 50L1350U only some leds out?

Originally posted by hfosteriii View Post

Question, is the forward voltage of the individual leds standard? I didn't know if smt Leda are the same as encapsulated leds. 3.2 volts or so each?

The Vf of the LED varies with If applied to the LED. You can use LED as long as the power is not exceed the spec.
Example:
https://www.badcaps.net/forum/showpo...7&postcount=31

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