Hitachi LED TV le24ecd05au turns on sometimes

[hernan_perez_br]

Hi, I have a problem with a Hitachi LED LCD TV with DVD combo model le24ecd05au.
It turns on just very few times around 5% of the tries, the other 95% it just turns the blue light on but nothing happes on the screen. But when it turns on successfully everithing works perfectly. It is a 12v 4a TV, so there is no power board inside the TV, just one board (i suspect is the main board) I can send you pictures if you want. Please help me as I want to fix it myself if I can. Thanks!

[multimeter]

Re: Hitachi LED TV le24ecd05au turns on sometimes

external power supply?,check its output voltage,could be cap related within the power brick

[hernan_perez_br]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Hi. thanks for your advise. as it is a 12v tv, I tried with different 12v external power supplies and with all of them it just power on successfuly very few times.
Thanks

[tom66]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Try heating/cooling parts on the main board up or down to see if the problem changes. Check all voltage regulators and dc-dc converters.

[hernan_perez_br]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Hi Tom66, Thanks for the reply. This is the mainboard I got http://1drv.ms/1hlZqDs
Could you please point me out where are the voltage regulators and the dc dc converter?
There is only one board on the TV.
Thanks all for the support

[tom66]

Re: Hitachi LED TV le24ecd05au turns on sometimes

See here for voltage regulators:
https://www.badcaps.net/forum/showthread.php?t=22231

[hernan_perez_br]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Hi, I will check the voltage regulators. One basic question, if I disconnect the screen from the mainboard, am I still in risk of an electric shock ?
The screen says "caution high voltage" but not the mainboard.
I am assuming that to check the voltage regulators, I have to have the plugged just the mainboard to the 12v external supply with all other things disconnected (lcd screen, etc)

Thanks!

[tom66]

Re: Hitachi LED TV le24ecd05au turns on sometimes

LED TV uses high voltage for string backlight, 40~120V for a 24". In either case, electric shock is possible, so you must take precautions and make sure to understand what you are testing.

[vinceroger69]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Hi, I will check the voltage regulators. One basic question, if I disconnect the screen from the mainboard, am I still in risk of an electric shock ?
The screen says "caution high voltage" but not the mainboard.
I am assuming that to check the voltage regulators, I have to have the plugged just the mainboard to the 12v external supply with all other things disconnected (lcd screen, etc)

Thanks!

i always leave all boards connected when i test them.

[hernan_perez_br]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Finally, I checked 3 different IC with code 1117B 3,3 542B, the value of the 3 legs are 5.60, 3.70 and 0.
Also there is another IC with code 1117B AD 931m with values 4.09, 2.12 and 0.69 in the 3 legs.
What else can I check?
Thanks for your help!

[hernan_perez_br]

Re: Hitachi LED TV le24ecd05au turns on sometimes

One thing I found is that when the does not turn on, the mainboard is sending 0.8 volts instead of 5v to the DVD board (this is a tv with integrated dvd combo).
but the 12v pint is OK, only the 5v pins are not getting the 5v.
Please see the attached image.
What could be the issue here to get less power? that is weird because sometimes it starts fine (very very few times). Also the power led is on and is a 5v led.
Thanks for the help !

Note: All the capacitors on the mainboard are EFC brand, they looks ok but I am not sure if that could be the reason.

[tom66]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Are you using a digital multimeter to check those regulators?

[hernan_perez_br]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Hi Tom, Yes I am using a digital multimeter. There are 3 regulators 1117B 3,3 542B (I cannot find the datasheet) and one regulator (i think is variable) 1117B AD 931m.
I do not understand why I am getting 5v in some places (the power led for example) but in others just 0.8v.
It is weird because 0.8v is the same value as one of the pins of the variable regulator.
I have no idea what to do next, just trying different things and external power supplies
Thanks for your help!

[tom66]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Please check your multimeter battery is not low, probably best to change it anyway. It can cause incorrect readings when low, the regulator with 3.6V on it should have 3.3V, etc.

[hernan_perez_br]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Hi Tom, you were right, I changed the battery and now the readings are these ones:
The voltage regulators with code 1117B 3,3 542B has values these values: 5.08v, 3.3v and 0v. The variable voltage regulator code 1117B AD 931m have these values" 3.52v, 1.86v and 0.6v
I still have the issue with the mainboard not supplying 5v in some cases, it supplies 0.64v but in the 12v line supplies 12.2v which is ok.
Looks like the 0.64v provided on the 5v line is similar to one of the pins of the variable regulator (0.6v)
What else can I check with the multimeter?
Thanks for your help!

[tom66]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Looks like that large copper orange coil/inductor is part of a dc-dc converter. It probably takes 12v input and produces the 5v rail. Can you get a closer picture of the area?

[hernan_perez_br]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Hi Tom, here are some pictures, let me know if you need more.
Thanks !

[tom66]

Re: Hitachi LED TV le24ecd05au turns on sometimes

OK, chip AIC2565 (looks like U3)

Check all pin voltages when unit is working, when it does not work and when in normal standby mode, need three sets of readings. All readings: red probe on pin, black probe on ground, DC 20V range.

pin 1 - BOOST, expect about Vin (12V) plus around 5 to 10V so ~17V to ~22V when working (use DC200V for this if your meter goes out of range)
pin 2 - VIN, expect about 12V (or adapter input voltage)
pin 3 - SW, expect about 5V out when working
pin 4 - GND, 0V
pin 5 - FB, expect around 1.22V when working
pin 6 - COMP, expect around 1.22V when working (though may be different - not certain)
pin 7 - EN, need to see, may be active high or low (ENABLE: this controls the chip being on or off) - hopefully same between ON and FAULTY
pin 8 - SS, the delay for controller start up, should be more than about 1V (SOFT START)

The pin 7 and pin 8 are most important - if pin 7 is different then the CPU is not turning the supply on or off, so the repair might be quite complex, need to test other things. On the other hand pin 8 capacitor is a frequent failure point and explains the low output voltage (0.8V) I'd normally expect 0V if it were a problem with CPU and enable pin.

[hernan_perez_br]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Hi Tom, These are the measures I did on the chip on stand by and with the power led on. but I could not measure it with the TV working. I tried many times and it does not turn on, I will keep trying and will upload the values when the tv works.
One more thing I noticed is when I measure the pint 7, it will restart the power led, if the power led is blue and I measure pin 7, the led will switch off and will turn to red (stand by).
Thanks !

[tom66]

Re: Hitachi LED TV le24ecd05au turns on sometimes

Looks like we need to look elsewhere.

My error on boost, it should be Vout+Vgs so 7.5V seems OK, guess it uses low Vgs FET or NPN.

Do you see that jumper block with 5V/3.3V printed on it... what do you measure on the pins connected to 5V? Note:- be careful not to short it.