RCA L32WD22 No 15v No 24v no backlight

[infringer]

Ok I have the LCD TV L32WD22 here and just as the title says I have no 15v no 24v and no backlight.

Obvious thing no 24v = no backlight

Anyhow I am curious.

I checked all caps with an ESR meter in circuit and all tested fine accept for one replaced that.

The ESR I have does not work for the 450v value so I replaced the cold side cap at 450v 100uf still a no go.

All voltage regs on main board test good the ones labeled for voltage tested at that voltage or close to it.

All the others tested within spec according to the datasheet. Which if I recall was like 5v and 2.8v.

Quite the oddity I've checked a few SMD diodes as well as radials and zenners just in case they all seem to throw a reading one way and none the other accept for 3 of the SMD which was somewhat typical for this SMD diode if I recall correct... .019 both ways on main board.

Finally I am at a loss as to where the 15v is not getting power and the 24v is not getting power the on off is 2.86v and the Dim is the same.

I am a bit curious on how to go further.

Note I never checked the hot side filter cap 450v 100uf it is the only large cap out of two that is on the board that did not get tested nor replaced.

This TV has been a nightmare thus far wasted an entire weekend on it with zero satisfaction usually I can figure this stuff out but I am stumped.

[newtothis]

Re: RCA L32WD22 No 15v No 24v no backlight

I would check the voltage across the hot 450v to see if it rises above 360v

Also have you disconnected main and forced PSU on to make sure nothing is dragging the lines down?

[infringer]

Re: RCA L32WD22 No 15v No 24v no backlight

no I have not disconnected but I will attempt it and report back.

[infringer]

Re: RCA L32WD22 No 15v No 24v no backlight

Hot side cap 450v 100uF = 160v

You sure it should be 360v if so there is an awful lot of R in that cap that should not be there I would assume?

I thought I read somewhere 160v is good possibly an old BudM post or something with this TV need to check for refs.

Video (Main Board) DC'd
15v = .22v
24v = .11v

both ways dc'd or not

5v is fine
12v is fine

Anyone out there ?

Still something is not checking out here... Seems like a SMPS issue but having troubles finding just where it is!

[budm]

Re: RCA L32WD22 No 15v No 24v no backlight

OK, step by step for most TVs: you need to find out of there is PS-ON signal coming from the main board or not when power switch is activated, if it does then you need to find out if the DCV between the two legs of the main filter cap has >360VDC, this boosted Voltage is generated by the PFC Voltage booster circuit (most TVs have this circuit) without it other power supply section will not work.

[infringer]

Re: RCA L32WD22 No 15v No 24v no backlight

PSON when switched on HOT filter cap is 160v

Got the Green led on power on.

I will check for PSON signal ... comming from main board.

THANKS!

I will check now as you specify.

[infringer]

Re: RCA L32WD22 No 15v No 24v no backlight

Mainboard These readings are with everything connected the TV the inverter the Tcon the Mainboard the switches the audio board and so on.

12 is 12.4
5 is 5.25

PSW pin on main video board goes from 5v to 3v

The filter cap on SMPS the cold side is 162.5v

The filter cap SMPS on the hot side is 160.2v

ON which is located on video main board connector goes from .4 when off to 4.5v when on.



PS which is located on video main board yet another connecter goes from .4 when off to 4.8v when on.

ON/OFF on the SMPS that goes to the TCON this is the only other label close to what you ask. .4 when switched off 3.2 when switched on.

Have a few TV boards lying around to do some parts robbery if need be willing to try any angle.

But nothing is labeled specifically PSON on the main board just as the above mentioned.

So from what is being said the Power Factor Correction Circuit is not working correctly what exactly is this comprised of and would this be considered active or non active and what makes it that way?

REASON FOR EDIT:

Uploading Pics of mainboard had to use shop jimmy camera battery is dead running on steam thanks!

[newtothis]

Re: RCA L32WD22 No 15v No 24v no backlight

PS_ON is the on off pin which in post one you said "on off is 2.86v and the Dim is the same." So you have >2.5v meaning the main is sending the correct voltage.

The main cap will show 160v when the TV is in standby and >360v when switched on. So you are not getting the boosted voltage on the PSU as it is not getting to >360v.

[Andrew F. Ali]

Re: RCA L32WD22 No 15v No 24v no backlight

When checking the voltage on the HOT side it is done with the -ve Black lead on the -ve pin of the Cap and the +ve Red lead is on the +ve pin of the HOT Cap

[budm]

Re: RCA L32WD22 No 15v No 24v no backlight

Can we see the whole back side of the TV? The ON/OFF pin is for the Inverter ON/OFF.
Also give the list of the pin names for those two connectors of the power supply board.

[infringer]

Re: RCA L32WD22 No 15v No 24v no backlight

Andrew F Ali,
Caps are labeled fairly well to tell the difference between negative and positive legs and often they are labeled well on the board as well and yes my leads are hooked into the correct ports unless there is something other I am not aware of the nice strip down the sides of the caps indicate the negative lead fairly well odd that you say that though the cap I had put on I almost put on backwards like a dummy heh good thing I like to check things twice before soldering them in so I had to reverse the bends on the legs.

newtothis,
As BudM stated yes it is to the inverter not the TCON sorry for the mixup on that one just called it the wrong thing for whatever reason can't explain it to be honest but it does not hook to the TCON it hooks to the inverter board assembly.

BudM,

1
2
3
4
5 +24v
6
7
8
9
10
11 DIM
12 ON/OFF
13 NC
14 NC

1
2 15v
3 12v
4
5 5v
6
7
8 GND
9
10
11
12
13 GND

Yes correct inverter not TCON sorry for the mix up...

I will note when checking for voltages I checked the pins next to what I thought was labeled 15 to the left and to the right just to be certain.

Same for the rest of the connections.

There were voltage readings on some of those pins not labled as well but a good instance is 12v had another 12v by it and 5v had another 5v by it and so on.

I suppose the connection to the cfl's under the heatshrink could be bad but it seemed like it was connected well when looking and tugging so I didn't check when I had the entire screen disassembled to check the cfl tubes for burns breaks and so on. But I doubt it the problem here is we get nothing off the power board so this is where the issue likely lies...

Hope this helps BudM

Sorry for the mess of wires had the thing all back together in a pile to test.

NOTE added a service manual I found online dunno how accurate it is for my particular model.

[budm]

Re: RCA L32WD22 No 15v No 24v no backlight

PS-ON is pin 11, so if what you show is correct (0V) then the main board is not sending the PS-ON signal.

[infringer]

Re: RCA L32WD22 No 15v No 24v no backlight

let me have a check at that one... I may have to upload a photo of my underside as I said this was a shopjimmy photo of the bottoms of the boards and fronts of the boards originally after checking I find there is like 4 versions of SMPS boards to this TV yikes! that normally says there was a ton of changes due to probably quality of design and cost savings to retrofit other products a bad model of TV to have imho but if I can fix it it'll make someone happy so going to give it some effort.

[infringer]

Re: RCA L32WD22 No 15v No 24v no backlight

getting 4v when the power is switched on on pin 11

getting 3.2v when the power is switched on on pin 12

(when I press the power button.)

Interesting thread seems similar to my issue but user does not say if he gets 15v or not... https://www.badcaps.net/forum/showth...hlight=L32WD22 I prefer crawling before walking but all stuff just to make a note of for me is the reason for posting the URL.

So what would be the next thing to follow providing it is "Getting signal to turn the pson"

Follow that pin back I would assume and start looking but rough knowledgeable guesses help a lot.

BTW if I havent said it thanks BudM for the help thus far.

[budm]

Re: RCA L32WD22 No 15v No 24v no backlight

If you do have PS-ON at pin 11, then you should have the PFC boosted Voltage on the main filter cap, if it stays at 160VDC then you need to troubleshoot the PFC section next.
You need to get the pinout of the PFC controller IC to see if it is getting the VCC Voltage to run.

[infringer]

Re: RCA L32WD22 No 15v No 24v no backlight

bottom of board

I will look into the PFC chip on the hot side

[budm]

Re: RCA L32WD22 No 15v No 24v no backlight

IC 901 (bottom left) is the PFC IC, need P/N as printed on top of the IC.
You need to check PFC Diodes D901 (SMD diode), D902 (mounted on the heatsink).

https://www.badcaps.net/forum/attach...1&d=1430872945

[infringer]

Re: RCA L32WD22 No 15v No 24v no backlight

Q903 on the side where the ac comes in on the board with the FBR is IC903 056T 379 61 IC LD7575PS SOP-8 LEADTREND

The side labled hot on my board is IC902 and this would be IC902 056T 564911 1 IC TEA1532CT SO-8

After close inspection the uploaded Manual and using the digital microscope I was able to make these two IC's out somewhat and fill in the blanks that the manual was correct on the numbering of the IC's

I will have to go looking for the datasheets but I have a power supply that is similar like this one and one of these is blown right off the board rather interesting to say the least ... And it is IC903 on that board as well...

[infringer]

Re: RCA L32WD22 No 15v No 24v no backlight

Errr sorry did not see your post in time was trying to number things out!

Let me give them a look.

UPDATE this one matches the service manual as well.

IC901 056T 368 12 IC FAN7529MX SOP-8

Pin 8 vcc it appears

VCC = 14V and TA = -40°C~125°C unless otherwise specified

UPDATE:

D901 and D902 pass diode test.

Trying to devise a way to have everything hooked up and upside down and check the voltage to that pin when powered on.

Start voltages is 11-13v it seems though according to the sheet.

[budm]

Re: RCA L32WD22 No 15v No 24v no backlight

So you are getting 14VDC for the VCC on pin 8, then that is OK.
If d901 is shorted then there will be no boosted Voltage, but the Diode is OK per your test.
Check and see if the Source resistor R921 is OK for the PFC MOSFET Q901, it should be <1 Ohm.
Also check the resistance between pin 7 Gate drive and the Ground pin 6 to see what you have.