rca rlded5078a-d

[dpcookson]

Re: rca rlded5078a-d

Sorry, don't mean to hijack this thread but I am curious if the OP solved their problem as I am experiencing the same issues with an identical board; my voltages to the LEDs read .689v

[CapLeaker]

Re: rca rlded5078a-d

Not that I know of.
However after your second or third post, you are able to do your own thread. You can use this one as a guide and report what you find.

[dpcookson]

Re: rca rlded5078a-d

Bear with me please, I am by no means an expert here, nor even a seasoned novice, lol.

Please correct me if i am mistaken,
After following the board layout according to SJ's pictures I have found that C10F may be the culprit as I have 358 VDC on the "south" side of the (cap?) but only 0.398 VDC on the "north" side.

Suspect device "C10F" is located below T2F (transformer at top of picture) on "HOT" side of board.

http://www.shopjimmy.com/proscan-ay1...upply-unit.htm

[budm]

Re: rca rlded5078a-d

C10F is the DC Blocking/Coupling cap and part of the Half-bridge drive circuit, one one of the cap is connected to the Primary side circuit circuit GND, anothe end is connected to one end of the primary xformer T2F. So one end of the cap will be 0V since it is connected to the primary circuit GND.
If the cap is bad (need to check its capacitance, common failure of that cap will be the lost of the capacitance) then there will be no output for the LEDs.

[dpcookson]

Re: rca rlded5078a-d

22.3 nf

Seems this cap is right on spec from what I have researched on it. Guess it's back to the drawing board, lol. Thanks for the help, I'm pretty new to this stuff so I appreciate any info I can get.

[budm]

Re: rca rlded5078a-d

There is that 18-pin SMD IC1F that drives the Gate Drive transformer T1F, if you can get the spec sheet to get the pin out to find out if that IC is working or not.

[dpcookson]

Re: rca rlded5078a-d

Okay, thanks for the suggestion. I'll take a look hopefully tomorrow night and see what I can find.

[smuddge]

Re: rca rlded5078a-d

no I haven't solved this yet. was away for a few days. I am looking forward to hearing if SMD IC1F is the problem.

[dpcookson]

Re: rca rlded5078a-d

IC1F is a BD9211F

I don't honestly know what I'm looking for to test this component so I took some voltage readings with my DMM while the board was wired up and powered on.

Pin # = VDC

1 = 11.14
2 = 4.15
3 = 0.001
4 = 1.465
5 = 0.023
6 = 0.020
7 = 0.001
8 = 0.096
9 = 0.001
10 = 3.495
11 = 0.001
12 = 0.001
13 = 0.003
14 = 0.002
15 = 0.025
16 = 0.001
17 = 0.001
18 = 0.001

I'm not sure if this is useful, any direction from here is appreciated though, thanks.

[budm]

Re: rca rlded5078a-d

Well, looking at the spec sheet, you do have 11VDC for the VCC pin 1 to run the IC, you also have >2vdc for the STB PIN 2 to turn on the IC.
There is not activity at the drive output pin 17, pin 18.
I do not understand the definition of the CP PIN 9 CP (timer latch detect voltage), 2vdc is the typical when it latch into shutdown or when it is running.
There is no application notes circuit to see how it is used.
I need to do more research on this IC, so far it looks like there is no activity from this IC.
May be you can monitor pin 9 when TV is OFF and when TV power switch is activated to see if it changes state.

[dpcookson]

Re: rca rlded5078a-d

Thank you budm for your time so far. I monitored the voltage on pin 9 while powering the unit on and off a couple times but there was no change.

[2cams70]

Re: rca rlded5078a-d

Hi Guys,

Greetings from Australia. Found an Aldi Bauhn ATV-50FHD3 TV courtesy of the kerbside shopping mall that seems to be a clone of this TV. Has the same issue. Have been right through the AY128D PCB checking MOSFETS replacing IC's (including one mentioned) and no success. I am coming to the conclusion that there is nothing wrong with the power board and that the problem lies with a faulty LED in the display causing the board to go into protection mode - this issue was found by another badcaps member somewhere in relation to another type of TV (search under "badcaps" and the LED driver IC type description). Will be a while until I get a chance to pull the screen apart to check though - any thoughts from you guys?

[dpcookson]

Re: rca rlded5078a-d

It just so happens that I already have mine tore down that far, I could test my strips if anyone can point me in the right direction.

[budm]

Re: rca rlded5078a-d

I would expect there will be the output to the LED strop first THEN the fault detection circuit kicks in, so it is either that the meter is too slow to show any Voltage spike at the LED's connector before it drops down to 0V as reported.

[CapLeaker]

Re: rca rlded5078a-d

If the problem is indeed a bad LED, I expect the LED driver circuit to come on and ramp up the voltage, then it senses an error, protection circuit kicks in and the voltage goes down. If there is no output at all on the LED driver and BLon is present, there has to be a problem somewhere on the board, or a dead short in the LED wiring. So to rule out the latter part, disconnect the LED's from the PSU and measure again.

[dpcookson]

Re: rca rlded5078a-d

Okay, measured the LED connector during power cycling and got -394V (why is this negative?) but it dropped out quickly like you guys said it might.

If this is a sign of a bad LED or more how do I check them? I tried setting my DMM to diode to test a few random ones but didn't seem to get anything.

[2cams70]

Re: rca rlded5078a-d

Hi dpcookson, would you be able to post a couple of pics of the screen LED's seeing as you have yours already in bits. Does this TV have edge or backlight LED's? Would appreciate it as I haven't dismantled mine that far yet - only gone as far as the PCB's.

[dpcookson]

Re: rca rlded5078a-d

It is full backlight, there are 5 strips of 14 LEDs.





note: The TV is "upside-down" in the pics

[CapLeaker]

Re: rca rlded5078a-d

Okay, measured the LED connector during power cycling and got -394V (why is this negative?) but it dropped out quickly like you guys said it might.

If this is a sign of a bad LED or more how do I check them? I tried setting my DMM to diode to test a few random ones but didn't seem to get anything.

That depends on where you had your GND lead from your DMM connected to during the measurement.
You can check every diode with your DMM set in diode mode and look for an open or dead short.

[dpcookson]

Re: rca rlded5078a-d

GND lead of the DMM was on the GND circuit of the board. On power up, the voltage at the LED connector started at +0.69V then about 3-4 seconds later it "dropped" to -394V, then returned to +0.69V. With the unit powered off there is 0V at the LED connector. I suppose it doesn't matter which side of the LED circuit is positive or negative, as long as the LEDs polarity matches.

I realize that an LED is a diode but maybe I was checking them wrong with my meter, if you look at my previous posted pictures, I was connecting my leads to each copper "dot" on both sides of an LED. I tried reversing the leads but came up with an open circuit on the few random LEDs I tested, makes me think I am doing something wrong, that or every LED is "NFG".