RCA L32HD31 - Power led indicator but no display

[caphair]

I have 5vsb but no 12v or 24v. Tried jumping PW to 5vsb and bl_on to 5vsb and still nothing. Tried measuring ac and frequency on the anode side of the dual package diode fed off the secondary of the switching transformer that's on the 12v line and got nothing.

Measured 170v on big cap on primary side so I'm guessing it has something to do with the Pfc not turning on.

Was I correct in jumping pw to 5vsb trying to turn rest of psu on for testing? Or do I need to jump it to ground as well as bl_on?

Also I'm confused why this board has both hot and cold grounds tied together with the blue wire?

**Please excuse my multiple posts with just one picture each as I currently don't have access to a computer and the site only uploads one pic per post from a phone**

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

Underside of psu

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

.

[budm]

Re: RCA L32HD31 - Power led indicator but no display

If you jump PS-0N with 1K to the 5VSTBY and the power supply board is not connected to the main board, then you should see close to 400V DC on the main filter cap if the PFC Voltage booster is working.
The 12V/24V SMPS needs that boosted Voltage to function

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

Ok doing that I still only get 170v so the pfc is not turning on. I noticed (what might be) a smd fuse at location RB5 coming off pin 4 of the standby transformer that measures open. But I have no idea what value fuse it is. It's green and has a C printed on it

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

I used a 0 ohm surface mount jumper, jumped pw on to 5vsb and all the voltages came up. 400v on main filter cap, 12/24v

Question, can I leave this jumper or do I need to figure out what was originally there?

[budm]

Re: RCA L32HD31 - Power led indicator but no display

That fuse feed the rectifier diode D83 as you can see, so you should check the resistance between the negative leg of the main filter cap and the Cathode of that D83.
I also see that the same transformer pin is also connected to R84 which also feeds another diode, what is the value of R84.
I really do not expect the fuse to be bigger than 1/4 A.

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

From cathode of D83 to negative of main filter cap is 33k ohms
Curious why you asked me to measure that resistance, to check for a short or?

R84 measures 24 ohms

[budm]

Re: RCA L32HD31 - Power led indicator but no display

From cathode of D83 to negative of main filter cap is 33k ohms
Curious why you asked me to measure that resistance, to check for a short or?

R84 measures 24 ohms

Yes, to find out if the fuse is blown due to heavy load (low resistance). You can temporary solder in fuse with legs just for testing.

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

Works fine with a 0 ohm surface mount jumper.

Can I leave that in or need to get proper fuse? What type would I need

[budm]

Re: RCA L32HD31 - Power led indicator but no display

You need to measure the dimension of the body and then go to DIGIKEY. I will not run with out it in place.

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

Ok. Can you explain why there's a wire tying the hot and cold grounds on the psu? This tv also only uses a two prong ac cord

[budm]

Re: RCA L32HD31 - Power led indicator but no display

That is not hot GND, they all are chassis GND which all tied to the metal chassis which is connected to safety GND of the incoming AC GND wire. You have LINE, NEUTRAL, and Safety GND (safety GND is for fault current) which is connected to the chassis, the cold side of the circuit GND is tied to the chassis safety GND/ The LINE and NEUTRAL will have Y type caps between LINE and Safety GND, Y cap between Neutral and safety GND. Do not confuse the primary side DC circuit GND which is GND ref point after the bridge rectifier.
Is the board mounted on the insulated plastic plate or metal plate? They usually rely on mounting screw to tie that metal rings on the circuit board to make contact with the metal chassis.

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

It's connected to the plastic back cover and the ac cord isn't three prong like I'm used to seeing so this had me stumped seeing it as hot/cold seem separated on the psu

[budm]

Re: RCA L32HD31 - Power led indicator but no display

Your TV is classified as double insulated device. So the parts used in side, I.E transformer has to be classified as double insulated.
http://www.gcsescience.com/pe38.htm
http://www.double-insulated.com/

They could have run the GND around the board mounting holes,
http://assets.shopjimmy.com/media/ca...bottom_2_1.jpg

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

Cool thanks never heard of double insulation. This board as well as the mainboard have some cables that screw into the metal chassis of the tv but I've only seen that when the GND of main AC cord is present

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

Btw I measured current across that smd fuse and it only draws 38ma

I also found a schematic and it oddly labels RB5 as 0 ohms. No fuse rating

[budm]

Re: RCA L32HD31 - Power led indicator but no display

I looks like that diagram is not updated to show the fuse (C) or the diagram is the newer revision and they removed the fuse, but if that Zener DB5 shorted out there will be no protection and hope that the SMPS IC will go into shutdown.
Are you keeping the TV or it belongs to customer?

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

It belongs to a friend of the family. I'm trying to expand my electronics repair knowledge so I offer to fix things for people I know to practice

[budm]

Re: RCA L32HD31 - Power led indicator but no display

Well it is up to you then, I myself do not believe it will cause much damage if something goes wrong if you put 0 Ohms jumper, more likely the circuit will go into startup/shutdown cycle.