42inch Touch Screen wont power on

[retiredcaps]

Re: 42inch Touch Screen wont power on

I pulled the IC off on the small Heatsinc it is DH18 B DM0465R

1) Datasheet is at



This is a FET/SMPS. Refer to figure 3 for the pinouts.

2) Pin 3 is Vcc and pin 2 is GND. Measure the resistance between these 2 pins. Report the reading.

3) According to the datasheet, when Vcc reaches 12 V DC, it starts working. After we tell you to reinstall everything, check Vcc to see if it gets to 12V DC.

4) Page 13 has a schematic.

[retiredcaps]

Re: 42inch Touch Screen wont power on

Check your pdf file. The formatting is all screwed up? I can't find 1-2, 1-3, etc.

If you can't get it looking correctly in the pdf, then post your xls file.

[epicfatigue]

Re: 42inch Touch Screen wont power on

resultrs from transformer 1 (large one)

[epicfatigue]

Re: 42inch Touch Screen wont power on

It is not uncommon to have more than 1 problem especially if the TV was subject to a power surge.

In the computer lcd world, some Benq boards have multiple problems. Bad caps, bad solder joints, open fuses, bad mosfets and bad transistors ALL can show up in one monitor. I know because I have fixed 5 or 6 of them.

Okay i just pulled everything off the board.

I will test both the transformers, i am testing the bridge rec out of circut.

I pulled the IC off on the small Heatsinc it is DH18 B DM0465R

can i do test 25# out of circut ? it tested okay last time sorry i thought i posted that.

[retiredcaps]

Re: 42inch Touch Screen wont power on

All voltages tested the same as they did before from the power points so guessing the diode wasnt the problem.

It is not uncommon to have more than 1 problem especially if the TV was subject to a power surge.

In the computer lcd world, some Benq boards have multiple problems. Bad caps, bad solder joints, open fuses, bad mosfets and bad transistors ALL can show up in one monitor. I know because I have fixed 5 or 6 of them.

[retiredcaps]

Re: 42inch Touch Screen wont power on

A) One still unanswered question from post #25.

1) See if pin 12 (vcc) is shorted to pin 10 (gnd). Any resistance reading less than 30 ohms suggests it is bad. If yes, I believe that indicates L659 is bad.

====

B) With the new diode in now, redo tests 3 and 4 in post #25.

====

New test.

c) On the biggest yellow transformer (the one above the Powerview logo), there are 17 pins on that transformer.

Number them however you like, but upload a picture with your numbering scheme so we know what it looks like. With power off and lcd unplugged measure the resistance and report all readings for the following pin combinations.

1-2, 1-3, 1-4, etc, etc, 1-16, 1-17
2-3, 2-4, etc, etc 2-17
3-4, 3-5, etc, etc, 3-17
etc
etc
14-15, 14-16, 14-17
15-16, 15-17,
finally
16-17

We are testing every possible pin combination with the above.

If possible, put it into a spreadsheet and export it as a PDF file so it is in a nice grid and we can read everything.

What we are looking for here is something obvious like an open winding when it shouldn't be. From the backside, you can tell which pins are supposed to have a low ohms reading (like 0.3).

[epicfatigue]

Re: 42inch Touch Screen wont power on

Hey all sorry back from holidays and still on them so have some decent time to do testing.

All voltages tested the same as they did before from the power points so guessing the diode wasnt the problem.

Marked as diagram
(1)
1-2 .243
2-1 ol
2-3 ol
3-2 .244
3-1 ol
1-3 ol
(2)
1-2 .196
2-1 ol
2-3 ol
3-2 .196
3-1 ol
1-3 ol

(3)
1-2 .196
2-1 ol
2-3 ol
3-2 .196
3-1 ol
1-3 ol
(4)
1-2 .193
2-1 ol
2-3 ol
3-2 .193
3-1 ol
1-3 ol
(5)
1-2 .193
2-1 ol
2-3 ol
3-2 .193
3-1 ol
1-3 ol
(6)
1-2 .195
2-1 ol
2-3 ol
3-2 .195
3-1 ol
1-3 ol

Retested

[tom66]

Re: 42inch Touch Screen wont power on

I think a better question/suggestion is

Have you retested the voltage at the connector with the replacement diode? It is a reasonable suggestion since one component has been changed and could produce new results?

If it was the same component reused or reinstalled, then I could see no point in retesting.

Good point. I am trying to deduce if the primary is switching at all.

[retiredcaps]

Re: 42inch Touch Screen wont power on

Have you tested the voltages out of that connector?

I think a better question/suggestion is

Have you retested the voltage at the connector with the replacement diode? It is a reasonable suggestion since one component has been changed and could produce new results?

If it was the same component reused or reinstalled, then I could see no point in retesting.

[epicfatigue]

Re: 42inch Touch Screen wont power on

Oh okay. Test the secondary side of the transformer. Every pin should measure short circuit or very close to. However, if the transformer is not working, there is little you can do to get a replacement.

Okay and if that checks out whats my next step so i can do more then one thing?

[tom66]

Re: 42inch Touch Screen wont power on

yes see post #16 that is what lead us the check the diodes,

we have found that the caps are not getting power the diodes test fine, how do i check the transformers or myabe the transistors on the other heatsincs?

Oh okay. Test the secondary side of the transformer. Every pin should measure short circuit or very close to. However, if the transformer is not working, there is little you can do to get a replacement.

[epicfatigue]

Re: 42inch Touch Screen wont power on

Have you tested the voltages out of that connector?

yes see post #16 that is what lead us the check the diodes,

we have found that the caps are not getting power the diodes test fine, how do i check the transformers or myabe the transistors on the other heatsincs?

[tom66]

Re: 42inch Touch Screen wont power on

Have you tested the voltages out of that connector?

[epicfatigue]

Re: 42inch Touch Screen wont power on

Okay, let's take a different angle of attack. Replace the diode with the new one. Post a picture of the connector going from the PSU to the main board.

A+B both go to the main board .

However if you notice before it there is a small heatsinc this contains a 6pin IC chip is this worth testing?

[tom66]

Re: 42inch Touch Screen wont power on

Okay, let's take a different angle of attack. Replace the diode with the new one. Post a picture of the connector going from the PSU to the main board.

[epicfatigue]

Re: 42inch Touch Screen wont power on

That is the correct way to test it. That's a very strange diode though - .099 would be extremely efficient. What is the part # on it?

New Part 838 MBR20100CT .225 (i got 2 of these both tested the same)
ORIGINAL B156N F30FC6 (the .099 one) Most were ranged between .198 - .178

[tom66]

Re: 42inch Touch Screen wont power on

Yes as stated above it till functioned as the others but in diode test it pased a much lower voltage it pasted .099 where the others passed as stated above in post #73

the method of testing is done as follows

1-2 Voltage (Red Pin 1 Black Pin 2)
2-1 OL (Black Pin 1 Red Pin 2)
2-3 OL (Red Pin 2 Black Pin 3)
3-2 Voltage (Black Pin 2 Red Pin 3)
3-1 OL
1-3 OL

That is the correct way to test it. That's a very strange diode though - .099 would be extremely efficient. What is the part # on it?

[epicfatigue]

Re: 42inch Touch Screen wont power on

Transformer would be rare. Did you test the failed diode you removed?

Yes as stated above it till functioned as the others but in diode test it pased a much lower voltage it pasted .099 where the others passed as stated above in post #73

the method of testing is done as follows

1-2 Voltage (Red Pin 1 Black Pin 2)
2-1 OL (Black Pin 1 Red Pin 2)
2-3 OL (Red Pin 2 Black Pin 3)
3-2 Voltage (Black Pin 2 Red Pin 3)
3-1 OL
1-3 OL

[tom66]

Re: 42inch Touch Screen wont power on

They all tested fine whats next?

red to pin 1 black to pin 2 .2XX
black to pin 1 red to pin to nothing

as diode only lets its pass one way its okay i am checking them right,

whats cahnces of it being the transformer?

Transformer would be rare. Did you test the failed diode you removed?

[epicfatigue]

Re: 42inch Touch Screen wont power on

All faulty would be very rare. Let's be sure you are testing them the right way. What mode do you have your multimeter on? Post a picture of it in that range.

They all tested fine whats next?

red to pin 1 black to pin 2 .2XX
black to pin 1 red to pin to nothing

as diode only lets its pass one way its okay i am checking them right,

whats cahnces of it being the transformer?