Hitachi L32S504 - Dead, No Power, No LED light

[ryanfan03]

I was given this TV and thought it would be an easy fix (bad caps or other components). I was wrong. This is my first thread so I hope I am doing this right. I am sort of still a novice.

I opened the set to check the components on the Power Supply. I checked for bulging caps. None. Checked the fuse. It's good. Then I checked most of the diodes and transistors and they are fine.

From lurking around these forums I learned how to check voltages of the connectors. I get 5V standby but nothing else (no PS/ON). After a little more research lead me to short the 5V pin with the PS/ON pin (with main board disconnected). With this set up I am getting 12V on both of the 12V pins but not 24V on those 2 pins.

So I am thinking that my PS is good and it is not getting any signal from the main?

Also the power button does nothing to the PS/ON voltage when pressed (Main Board connected).

I guess I am asking if I am right in thinking the Main Board to be the probable culprit. And if so what are some things I can check on it. I tried to test what I thought were the voltage regulators but I was not getting any readings for any pins of any of them while the AC was plugged in. Either I did it wrong, those are not voltage regulators, or have a completely dead main board.

Any help is appreciated. I can take more/better pictures (well I will try at least) if need be.

[budm]

Re: Hitachi L32S504 - Dead, No Power, No LED light

Are there any Voltage labels on those two connectors on the top edge of the power supply board?

[ryanfan03]

Re: Hitachi L32S504 - Dead, No Power, No LED light

yes sorry about that:

CN902 to the main board (top right in picture) from left (middle of board) to right (end of board):

ON/OFF
DIM
+12V
+12V
GND
GND
GND
+24V
+24V
PS/ON
+5V
+5V

CN903 (to the inverter) I did not check/test anything on this.
from left (edge of board) to right (middle of board):
+24V
+24V
+24V
+24V
+24V
GND
GND
GND
GND
GND
DET
ON/OFF
DIM

[budm]

Re: Hitachi L32S504 - Dead, No Power, No LED light

That's great, so take the DC Voltage readings on CN902 when TV is off, and when power switch is activated, the one I am interested in is the PS_ON pin, it should change state when TV goes from off to ON and when from On to OFF.
for example:Notes, no need to check GND pins.

ON/OFF pin: OFF = xxV, ON = xxV
DIM pin: OFF = xxV, ON = xxV
+12V pin:
+12V pin:
GND
GND
GND
+24V pin:
+24V pin:
PS/ON pin:
+5V pin:
+5V pin:

[ryanfan03]

Re: Hitachi L32S504 - Dead, No Power, No LED light

OK I will have to do that tomorrow (something came up and I can not do it right now). I did this with the PS/ON pin and nothing changed when the button was pushed (0V). I will check again along with the rest of the pins. Appreciate the reply.

[budm]

Re: Hitachi L32S504 - Dead, No Power, No LED light

OK, if the main board is receiving the +5V for it to function and If the PS_ON does not change state when power switch is activated then the problem will be some where on the main board, this PS_ON is one of the most important signal, it is used to turn on the 12V and the 24V power supply, and the PFC Voltage booster circuit.

[ryanfan03]

Re: Hitachi L32S504 - Dead, No Power, No LED light

OK so I hooked it up and checked the voltage at PS/ON...no change (0V) when the button is pushed or the remote is used. I checked the pin for the 5V on the Main Board connector (from the power supply) and that was present. This means that the power supply is supplying 5V to the main for it to do its thing and it is failing? What can I check on the main board? I dont have much experience with surface mount components.

[budm]

Re: Hitachi L32S504 - Dead, No Power, No LED light

I cannot see that well from your pictures, I would check to see if it has any fuses on the main board, check the Voltages of the 3-pin Voltage regulator ICs, good visual inspection for damaged components, etc.
Check Shopjimmy.com to see what the replacement board will be.
Did it go out by itself or it was hit by surges or lightnings?

[ryanfan03]

Re: Hitachi L32S504 - Dead, No Power, No LED light

I will be sure to check for fuses when I get home. The voltage regulator (I think it is one) that is just under the connector didn't have any readings before. I will have to review that post and video to make sure I did it correctly. I do not know exactly how it went out. I know I stated I was given this tv but this might be one I picked up off of craigslist for $5. I do that for cases like this where I can learn to fix them.

[ryanfan03]

Re: Hitachi L32S504 - Dead, No Power, No LED light

So I went to check for fuses on the Main Board. I didn't see any with a quick scan so I started looking for VR ICs. I cam across this one pictured. Obviously I know this will interfere with the overall operation but will this kill the entire board so NO voltage is present? Or will I have to replace it and find out. This will be a good test for me as I have not changed one of these yet. Hopefully it will not cost me too much.

[budm]

Re: Hitachi L32S504 - Dead, No Power, No LED light

That U702 output pin (Left pin) is broken off? Someone must have worked on this board before.

[ryanfan03]

Re: Hitachi L32S504 - Dead, No Power, No LED light

That's what it looks like. I'll replace it if it's cheap enough. Hopefully the person just decided to give up on the project and this is all that needs to be done. How would I go about ordering the part? Just google the number on the part itself?

[lookimback]

Re: Hitachi L32S504 - Dead, No Power, No LED light

I believe this is the datasheet for that VR. Checked Digikey and Mouser, no luck.

Ebay has some listed if you don't mind waiting a few weeks because they're in China. You should be able to substitute it though. It's a 5A low dropout positive adjustable regulator in a TO-252 package. The default output voltage is 1.8v.

[ryanfan03]

Re: Hitachi L32S504 - Dead, No Power, No LED light

I was just snooping around digikey myself. Came across this...would it work?

http://www.digikey.com/product-detai...GCT-ND/2122989

[lookimback]

Re: Hitachi L32S504 - Dead, No Power, No LED light

Possibly. I'm not sure if the input voltages are the same. The data sheet I uploaded doesn't really say, unless I'm missing it. I think Bud is better qualified to answer this than I.

[budm]

Re: Hitachi L32S504 - Dead, No Power, No LED light

I was just snooping around digikey myself. Came across this...would it work?

http://www.digikey.com/product-detai...GCT-ND/2122989

That is the correct one, it is 1.8V Fixed output regulator.

[budm]

Re: Hitachi L32S504 - Dead, No Power, No LED light

I wonder why that input leg is cut, you should check the resistance of that pad where the missing leg is connected to and ground, also between the big tab and ground.

[ryanfan03]

Re: Hitachi L32S504 - Dead, No Power, No LED light

OK I will do that right now. This would be unplugged I am assuming. And what should I be looking for 0 ohms? Be right back...

[ryanfan03]

Re: Hitachi L32S504 - Dead, No Power, No LED light

Just tested. Reading zero for both. Two things interesting though. First, after being curious I tested two other VRs. One (U703) read zero, the other (U708) had a reading of a few k ohms. And second I saw an open spot that looked like a cap was missing...looked closer and saw two legs sticking out of the holes. I don't know what is going on but now I have to find the value of that cap (C702).

[budm]

Re: Hitachi L32S504 - Dead, No Power, No LED light

It should show >500 Ohms, that is what I expect, TV is unplugged.
Zero means bad, so I think the person was cutting the lead off the regulator trying to find where the shorted circuit is by isolating it.
It looks like the person messed up the board also, I wonder what else is missing.
BTW, you checked the resistance with the TV unplugged, right?