Samsung LA32R81B Not Turning On

[kgavionics]

Re: Samsung LA32R81B Not Turning On

Have you tested all the diodes and Mosfets on the 12V and 24V rails?

[killpatrick]

Re: Samsung LA32R81B Not Turning On

hi guys,

Just an update, so replace the fuse, then did a voltage reading from the hot side, from these resistors that are series from the main cap, RM819 378V - 251V, RM820 251V - 171V, RM821 171V - 109V, RM822 109V - 59V, RM823 59V - 2.5, RM824 2.5 - 0V. If I remove these SMD resistor, can I replace them with the regular resistor with the same value? Also if that is possible, what is the wattage should I use? It is not indicated on the diagram, for example the RM819 it says 200KF/2012 so the replacement should be a 200k resistor? But what wattage should I use? Thanks guys, learning a lot from this forum.

[killpatrick]

Re: Samsung LA32R81B Not Turning On

I have removed these resistors and tested them and they are within tolerance, RM819 240K = 237K, RM820 240K = 237K, RM821 240K = 237K, RM822 200K = 197K, RM823 200K = 197K, RM824 11K = 10.83K.

[killpatrick]

Re: Samsung LA32R81B Not Turning On

Tried to do further voltage checking, with the icm801(mc33067) outout pin12 has a 14V but on the output pin14 I only have 0.29V, should it have the same output voltage? These output are going to the TM802 which I think will pass thru TM801S, the TM801S does not have any output. thanks again.

[dick_barton]

Re: Samsung LA32R81B Not Turning On

The 2.5V looks good at the end of the resistor chain so I would leave them in circuit. What voltage do you have on Pin 15 and Pin 5 of MC33067

The outputs at Pin 12 (Output B) and Pin 14 (Output A) are in opposition to each other. When one goes high the other low and vice-versa so that's not the problem.

[killpatrick]

Re: Samsung LA32R81B Not Turning On

hi dick, thanks for the response. well i still get the 15.04 on the vcc and on vref still getting 5.02. I see, learning new things. I though the ic is bad,

[dick_barton]

Re: Samsung LA32R81B Not Turning On

I forgot that I had already asked you for VCC and Vref.
In the picture (red arrow pointer) there's an electrolytic capacitor alongside the ICM801 which looks as though one leg is not soldered. Can you check it out.

[killpatrick]

Re: Samsung LA32R81B Not Turning On

Hi dick, thanks for the response, it is soldered, I have fix that leg sorry bout that picture.

[dick_barton]

Re: Samsung LA32R81B Not Turning On

What voltage do you have on pin 9, "Enable" of MC33067

[killpatrick]

Re: Samsung LA32R81B Not Turning On

For the pin 9, I have 14.5V.

[dick_barton]

Re: Samsung LA32R81B Not Turning On

The voltages around that IC do not seem out of place.

With the power off can you measure the resistance between
chassis and 24V pin =
chassis and 13V pin =
chassis and 12V pin =
chassis and 5.3V pin =

[killpatrick]

Re: Samsung LA32R81B Not Turning On

thanks for the response, should I connect the mainboard and the inverter board as well? Or just screw in the power board to the chassis and do the test?

[dick_barton]

Re: Samsung LA32R81B Not Turning On

There is no need to connect anything to the power supply. Its a quick test with the power off to see if there is a problem on the secondary supply which could be stopping it from fully working. It just the resistance reading of each supply that's being checked.

[killpatrick]

Re: Samsung LA32R81B Not Turning On

thanks, did what you ask and here is my readings. DMM is set to x200

Test leads = Positive lead to ground and Negative to PINS.

24V = 91.6
13V = 97.1
12V = 0 or no reading
5.3V = 80.6

If I reverse the leads, I have no readings.

Thanks,

[dick_barton]

Re: Samsung LA32R81B Not Turning On

thanks, did what you ask and here is my readings. DMM is set to x200

Test leads = Positive lead to ground and Negative to PINS.

24V = 91.6
13V = 97.1
12V = 0 or no reading
5.3V = 80.6

If I reverse the leads, I have no readings.

Thanks,

A reading of 0 = zero ohms which is a short circuit. If it is definately not OL, which is overload ie greater than x200, then you have a problem with ICM853 or CM858.
Can you measure the resistance of the 4 pins of ICM853

[killpatrick]

Re: Samsung LA32R81B Not Turning On

Apologies, not zero but no reading. My DMM will display 1 is there are no reading, then 0 if I short the leads.

[dick_barton]

Re: Samsung LA32R81B Not Turning On

OK, so there is no obvious issues with the scondary supplies.
Need to think about this further.

[killpatrick]

Re: Samsung LA32R81B Not Turning On

thank you for your patience in helping me with this power supply. really appreciate it.

[dick_barton]

Re: Samsung LA32R81B Not Turning On

Can you measure the capacitance of CM808 and check that it's not bulged or damaged.

[killpatrick]

Re: Samsung LA32R81B Not Turning On

okay, remove the cm808, then tried to test it on capacitance set to X20n, without touching the lead my meter has 0.02, short the capacitor, then tried to test it, first reading was 1.27, then short it again to test, 1.26, reverse the test leads and short the cap again, 1.25 ans so on, I can't seem to get a consistent reading with this cap. I stop on 1.19