Curtis lcd3215a Standby power only

[allsmith]

Re: Curtis lcd3215a Standby power only

The Diode is OK, yes change that start up cap first with what you have just to test it as long as you know that the replacement cap is good, that is the catch.
By the way, were you able to test the pin7 VCC pin of the IC?

Ok thanks i'll look and see if i can find a different start up cap.

I have not tested pin 7 for VCC yet, I think Tom was gonna have me solder a wire to it so i can set the board back in tv and still be able to test pin 7.

Could i connect the board to ground with a wire and stand up the power supply secured and propped up by a roll of paper towels or something like that and power supply connections all plugged in to test pin 7?

[budm]

Re: Curtis lcd3215a Standby power only

The Diode is OK, yes change that start up cap first with what you have just to test it as long as you know that the replacement cap is good, that is the catch.
By the way, were you able to test the pin7 VCC pin of the IC?

[allsmith]

Re: Curtis lcd3215a Standby power only

Not sure if you have already changed/checked these components or not.

I have tested the diode you pointed out.
Auto range meter on diode test in circuit.
Diode=
positive to bar= .49
negative to bar= OL

The resister you pointed out R29
Auto range meter set to ohms.In circuit.
=73.8
Reverse=72.5

I dont know how to test the ceramic or film cap that is with the diode and resistor

I have not changed any of the small electrolytic caps,only the two bigger ones that where slightly puffed.(pic in my first post)

Could i replace the small electrolyic caps that you pointed out with some caps from a couple computer power supplies that i have? As long as the capacitance and voltage are the same? Just for testing,then i'll order new ones,if i get it working.

Thanks!

[budm]

Re: Curtis lcd3215a Standby power only

"1" is printed right on the board, at the bottom left pin where the IC is. Number 8 is printed right on the board by the top left pin of the IC.

[allsmith]

Re: Curtis lcd3215a Standby power only

OK pin 7 is Vcc.

Next to pin 1 there should be a small dot (sunk in the epoxy package)... could you mark this dot on an image as I'm having difficulty making it out on the image.

Sorry Tom,there is no indent circle on KA3843B,Even tried 20x magnification.
I hope it wasnt painted on and it rubbed off when i quickly cleaned the devise with a q-tip and rubbing alcohol! The other IC's on the board have the indent,Have you ever seen them painted on??

[budm]

Re: Curtis lcd3215a Standby power only

error: double posted

[budm]

Re: Curtis lcd3215a Standby power only

Not sure if you have already changed/checked these components or not.

[tom66]

Re: Curtis lcd3215a Standby power only

OK pin 7 is Vcc.

Next to pin 1 there should be a small dot (sunk in the epoxy package)... could you mark this dot on an image as I'm having difficulty making it out on the image.

[budm]

Re: Curtis lcd3215a Standby power only

[allsmith]

Re: Curtis lcd3215a Standby power only

i'm talking about the little black chips on the bottom of the board. Each of these has a voltage supply called vcc. A failed vcc supply could explain the problem and it's a fairly common problem with power supplies. It looks like the only way to probe is from the bottom.

Since the standby is good (you have a standby led and pson goes high to 5v), the problem is almost certainly with the main power supply, which generates the 24v, and likely other rails like 12v, too.

Can you get the part # of the device i've circled in the image?

ic2
3843b
stez749

[tom66]

Re: Curtis lcd3215a Standby power only

Sure i can try anything you want me too,i appreciate the help!!

Now are we talking about the 4 rectifiers on the one heat sink,that are giving me trouble testing? Or are we good there and your onto something else?

Explain to me what the contoller Vcc is please
Not exactly sure what that is

Thank you!

I'm talking about the little black chips on the bottom of the board. Each of these has a voltage supply called Vcc. A failed Vcc supply could explain the problem and it's a fairly common problem with power supplies. It looks like the only way to probe is from the bottom.

Since the standby is good (you have a standby LED and PSON goes high to 5V), the problem is almost certainly with the main power supply, which generates the 24V, and likely other rails like 12V, too.

Can you get the part # of the device I've circled in the image?

[allsmith]

Re: Curtis lcd3215a Standby power only

OK so this means pin 3 is source, pin 2 is drain and pin 1 is gate (by deduction). The FETs look good. I am trying to work out a way to test controller Vcc. It may involve soldering a wire to a pin and testing that instead (as the Vcc pin is on the bottom), if you are OK to do that?

Sure i can try anything you want me too,i appreciate the help!!

Now are we talking about the 4 rectifiers on the one heat sink,that are giving me trouble testing? Or are we good there and your onto something else?

Explain to me what the contoller Vcc is please
Not exactly sure what that is

Thank you!

[Th3_uN1Qu3]

Re: Curtis lcd3215a Standby power only

Btw, for the diodes, i meant "try unsoldering one end". Sorry, i was in a hurry.

[tom66]

Re: Curtis lcd3215a Standby power only

OK so this means pin 3 is source, pin 2 is drain and pin 1 is gate (by deduction). The FETs look good. I am trying to work out a way to test controller Vcc. It may involve soldering a wire to a pin and testing that instead (as the Vcc pin is on the bottom), if you are OK to do that?

[allsmith]

Re: Curtis lcd3215a Standby power only

Q10 may, or may not be open. Without giving a part ID i can't tell for sure.

As for the diodes, try unsoldering one and and testing them that way on the diode test.

Q10
P40NF03LA
n channel mosfet

test in circuit Dmm set to diode
1-2=OL
2-1=OL
2-3=OL
3-2=540
1-3=OL
3-1=OL

Q8
P40NF03LA

1-2=OL
2-1=OL
2-3=OL
3-2=546
1-3=OL
3-1=OL

Q8 & Q10 in red box in pic

[Th3_uN1Qu3]

Re: Curtis lcd3215a Standby power only

Q10 may, or may not be open. Without giving a part ID i can't tell for sure.

As for the diodes, try unsoldering one and and testing them that way on the diode test.

[allsmith]

Re: Curtis lcd3215a Standby power only

I can help with the easy bits

I dont know how others do it I have a labour intensive method
To reply click on Blue "quote" right hand side
Highlight and press delete to get rid of bits you dont want
To answer multiple bits with answers between I Highlight and cut the
Sq Bracket/QUOTE Sq Bracket and place it at the end of each part I want to quote and do the same for the SqBracket QUOTE Sq Bracket (delete =allsmith;261886 ) and place it at the beginning. You could of course just type Sq Bracket etc where you wanted it.

Just to check you have it right instead of posting go to preview post.
It is a lot simpler to do than to explain how to do it!!!

thanks! i'll keep trying,I tried it once like you do it and think i deleted one of sq Brackets and then it didnt show up in blue.

[allsmith]

Re: Curtis lcd3215a Standby power only

I think the main board is fine. Since PSON is rising, the PSU is the fault.

There are a few possibilities, the most likely is a shorted diode or startup cap.

Let's try diodes first -

All tests done with power supply unplugged and removed from TV.

Red circled diode: Test from the indicated arrow direction (positive) to the bar (negative) - you should get around 300 to 800. Then reverse the leads, it should read "1".

Blue circled diodes: Check each other pin to the center pin, in all directions. For example, if you numbered the pins from 1 to 3 starting from the top, you should test: 1->2, 2<-1, 3->2, 2<-3. And you should get readings of around 100 to 600 for each of the "->", but "1" for each "<-".

Orange circled device - please check what the designator is. Is it "Dxxx" or "Qxxx"? (where xxx is a 3 digit number)

Diode circled in red...DMM on diode test
Positive to bar=540
reverse=1/OL

Devise in orange is designated as Q10(I believe is a mosfet,too close to heat sink to read part#)Test done with DMM set to diode test=

Q10
1-2=540
2-1=1/OL IS Q10 reading failed open here?
2-3=1/OL
3-2=1/OL

Devises in blue are from top to bottom of pic

D10
B304G
switchmode rectifier

D15
sf1603g
rectifier

D6
stp520150ct
high voltage
schottky
rectifier

These D designation devises are the ones im having trouble testing
originaly i tested them on 200 ohm setting and find all of them to read shorted

how would i test these rectifiers??
With diode test or ohm test
Diode test is erratic and will even cause the Dmm to beep continuity

[selldoor]

Re: Curtis lcd3215a Standby power only

Also how do i Quote just part of somebodys post and get it to show up in blue like you are doing?? I cant figure it out!! Man! not only am i a noob at electronics and photography! im also a noob at forums!! lol sorry

I can help with the easy bits

I dont know how others do it I have a labour intensive method
To reply click on Blue "quote" right hand side
Highlight and press delete to get rid of bits you dont want
To answer multiple bits with answers between I Highlight and cut the
Sq Bracket/QUOTE Sq Bracket and place it at the end of each part I want to quote and do the same for the SqBracket QUOTE Sq Bracket (delete =allsmith;261886 ) and place it at the beginning. You could of course just type Sq Bracket etc where you wanted it.

Just to check you have it right instead of posting go to preview post.
It is a lot simpler to do than to explain how to do it!!!

[tom66]

Re: Curtis lcd3215a Standby power only

I think the main board is fine. Since PSON is rising, the PSU is the fault.

There are a few possibilities, the most likely is a shorted diode or startup cap.

Let's try diodes first -

All tests done with power supply unplugged and removed from TV.

Red circled diode: Test from the indicated arrow direction (positive) to the bar (negative) - you should get around 300 to 800. Then reverse the leads, it should read "1".

Blue circled diodes: Check each other pin to the center pin, in all directions. For example, if you numbered the pins from 1 to 3 starting from the top, you should test: 1->2, 2<-1, 3->2, 2<-3. And you should get readings of around 100 to 600 for each of the "->", but "1" for each "<-".

Orange circled device - please check what the designator is. Is it "Dxxx" or "Qxxx"? (where xxx is a 3 digit number)