Benq Q7T3 - No Power

[matthmal]

Hi,

I have this Benq Q7T3 monitor that has no power.

What I have done:
- I checked the fuse and it seems fine
- I looked at the caps and their appearance is fine
- I tested the C5707 transistors and their resistance is much more than 20 although at the back of the board they don't look good.
- tested the big cap and the voltage is 320V

Any help please?

Thanks,
Matthew

[retiredcaps]

Re: Benq Q7T3 - No Power

Check Q805 and Q812 for shorts. They are likely FU9024. See if PF801 fuse is open or not.

PS. This board is widely documented with all the known problems.

[matthmal]

Re: Benq Q7T3 - No Power

POWER OFF 2000ohms

Q805

Pin 1 to Pin 2 -> 687
Pin 1 to Pin 3 -> 981
Pin 2 to Pin 3 -> It will start to give a reading, until it goes up to 1998 but it will then end up with 1 (out of range)

Q812

Pin 1 to Pin 2 -> 684
Pin 1 to Pin 3 -> 957
Pin 2 to Pin 3 -> It will start to give a reading, until it goes up to 1998 but it will then end up with 1 (out of range)

PF801

Result is 000

The reading that there was on those transisters is:
D1OPF
06
GKOLS508

Note: I have just noted a little leak with one leg of the big cap. When i tested the big cap it read 320V but on the cap is supposed to be 450V 100uF

[matthmal]

Re: Benq Q7T3 - No Power

I have done the following four tests on the transformers, results are posted below:

Tranformer 1 Test (T801):

Pin 1 to Pin 2 -> 204
Pin 1 to Pin 3 -> 1
Pin 1 to Pin 4 -> 391
Pin 1 to Pin 5 -> 391
Pin 1 to Pin 6 -> 392
Pin 1 to Pin 7 -> 391
Pin 1 to Pin 8 -> 1

Pin 2 to Pin 3 -> 1
Pin 2 to Pin 4 -> 1
Pin 2 to Pin 5 -> 1
Pin 2 to Pin 6 -> 1
Pin 2 to Pin 7 -> 1
Pin 2 to Pin 8 -> 1

Pin 3 to Pin 4 -> 745
Pin 3 to Pin 5 -> 745
Pin 3 to Pin 6 -> 745
Pin 3 to Pin 7 -> 745
Pin 3 to Pin 8 -> 000

Pin 4 to Pin 5 -> 000
Pin 4 to Pin 6 -> 000
Pin 4 to Pin 7 -> 000
Pin 4 to Pin 8 -> 1653

Pin 5 to Pin 6 -> 000
Pin 5 to Pin 7 -> 000
Pin 5 to Pin 8 -> 1651

Pin 6 to Pin 7 -> 000
Pin 6 to Pin 8 -> 1651

Pin 7 to Pin 8 -> 1653

[matthmal]

Re: Benq Q7T3 - No Power

Tranformer 2 Test (T802):

Pin 1 to Pin 2 -> 203
Pin 1 to Pin 3 -> 1
Pin 1 to Pin 4 -> 1371
Pin 1 to Pin 5 -> 1371
Pin 1 to Pin 6 -> 1371
Pin 1 to Pin 7 -> 1371
Pin 1 to Pin 8 -> 1

Pin 2 to Pin 3 -> 1
Pin 2 to Pin 4 -> 1
Pin 2 to Pin 5 -> 1
Pin 2 to Pin 6 -> 1
Pin 2 to Pin 7 -> 1
Pin 2 to Pin 8 -> 1

Pin 3 to Pin 4 -> 1
Pin 3 to Pin 5 -> 1
Pin 3 to Pin 6 -> 1
Pin 3 to Pin 7 -> 1
Pin 3 to Pin 8 -> 000

Pin 4 to Pin 5 -> 000
Pin 4 to Pin 6 -> 000
Pin 4 to Pin 7 -> 000
Pin 4 to Pin 8 -> 1

Pin 5 to Pin 6 -> 000
Pin 5 to Pin 7 -> 000
Pin 5 to Pin 8 -> 1

Pin 6 to Pin 7 -> 000
Pin 6 to Pin 8 -> 1

Pin 7 to Pin 8 -> 1

[matthmal]

Re: Benq Q7T3 - No Power

Tranformer 3 Test (T803):

Pin 1 to Pin 2 -> 205
Pin 1 to Pin 3 -> 1
Pin 1 to Pin 4 -> 1
Pin 1 to Pin 5 -> 1
Pin 1 to Pin 6 -> 1
Pin 1 to Pin 7 -> 1
Pin 1 to Pin 8 -> 1

Pin 2 to Pin 3 -> 1
Pin 2 to Pin 4 -> 1
Pin 2 to Pin 5 -> 1
Pin 2 to Pin 6 -> 1
Pin 2 to Pin 7 -> 1
Pin 2 to Pin 8 -> 1

Pin 3 to Pin 4 -> 739
Pin 3 to Pin 5 -> 739
Pin 3 to Pin 6 -> 740
Pin 3 to Pin 7 -> 739
Pin 3 to Pin 8 -> 000

Pin 4 to Pin 5 -> 000
Pin 4 to Pin 6 -> 000
Pin 4 to Pin 7 -> 000
Pin 4 to Pin 8 -> 1651

Pin 5 to Pin 6 -> 000
Pin 5 to Pin 7 -> 000
Pin 5 to Pin 8 -> 1651

Pin 6 to Pin 7 -> 000
Pin 6 to Pin 8 -> 1651

Pin 7 to Pin 8 -> 1650

[matthmal]

Re: Benq Q7T3 - No Power

Tranformer 4 Test (T804):

Pin 1 to Pin 2 -> 199
Pin 1 to Pin 3 -> 1
Pin 1 to Pin 4 -> 1
Pin 1 to Pin 5 -> 1
Pin 1 to Pin 6 -> 1
Pin 1 to Pin 7 -> 1
Pin 1 to Pin 8 -> 1

Pin 2 to Pin 3 -> 1
Pin 2 to Pin 4 -> 1
Pin 2 to Pin 5 -> 1
Pin 2 to Pin 6 -> 1
Pin 2 to Pin 7 -> 1
Pin 2 to Pin 8 -> 1

Pin 3 to Pin 4 -> 1
Pin 3 to Pin 5 -> 1
Pin 3 to Pin 6 -> 1
Pin 3 to Pin 7 -> 1
Pin 3 to Pin 8 -> 000

Pin 4 to Pin 5 -> 000
Pin 4 to Pin 6 -> 000
Pin 4 to Pin 7 -> 000
Pin 4 to Pin 8 -> 1

Pin 5 to Pin 6 -> 000
Pin 5 to Pin 7 -> 000
Pin 5 to Pin 8 -> 1

Pin 6 to Pin 7 -> 000
Pin 6 to Pin 8 -> 1

Pin 7 to Pin 8 -> 1

[matthmal]

Re: Benq Q7T3 - No Power

can someone please help?

[selldoor]

Re: Benq Q7T3 - No Power

Too many numbers - Transformer 4 looks definitely off ( your not having much luck)

I attach a pic which I think shows the joints for the secondary windings
Power off meter on 2000 ohms test s1>s2 s3>s4 s5>s6 s7>s8

looks like there maybe 2 pins for each S number - just check that that are
connected together. If it is one of these:
http://www.ipertronica.it/catalogo/R...26038001-35586

ti parlano italiano?

[matthmal]

Re: Benq Q7T3 - No Power

we for every s number there is only one leg, the other is only solder.

Here are the readings

S1 to S2 -> 203
S3 to S4 -> 202
S5 to S6 -> 203
S7 to S8 -> 198

Io non parlo molto italiano

[selldoor]

Re: Benq Q7T3 - No Power

Well they look a lot better - I dont think they often fail
on this board ( famous last words)

You did check all 4 5707s?

I cant see that you have listed any voltages out on CN 702
However I cant really advise you to carry on with any POWER ON Tests as you have said the Big Cap is Leaking. The voltage is actually ok but once air replaces the escaping electrolyte and it gets hot it could explode!!!

When you have got it replaced it would be useful if you can say what happens from switch on to stable fault stage.
What does the screen do what does the power light do any sounds clicks hisses and so on.

You could also do some none powered tests on the components
on the heatsinks and on the black barrel diodes D601 and one just behind the heatsink near the "15"

If you have not yet done so you need to resolder ALL the
joints on the inverter transformers the 5707s and the black box caps between the 5707s.It cannot be emphasised enough how important this is

[matthmal]

Re: Benq Q7T3 - No Power

5707 Transister Test 1:

Pin 1 to Pin 2 -> 1641
Pin 1 to Pin 3 ->1966
Pin 2 to Pin 3 > 170

5707 Transister Test 2:

Pin 1 to Pin 2 -> 176
Pin 1 to Pin 3 -> 177
Pin 2 to Pin 3 > 1458

5707 Transister Test 3:

Pin 1 to Pin 2 -> 725
Pin 1 to Pin 3 ->725
Pin 2 to Pin 3 > 1403

5707 Transister Test 4:

Pin 1 to Pin 2 -> 726
Pin 1 to Pin 3 -> 726
Pin 2 to Pin 3 > 1408

D601 Test :

518

D602 Test :

580

Please note that all tests were carried out with POWER OFF and 2000ohms.

I will carry out more tests tomorrow and try to re-solder the C5707s

[budm]

Re: Benq Q7T3 - No Power

You should test these transistors out off the board, and try using ECB instead as shown here:
http://s807.photobucket.com/albums/y...t=DSCF0766.jpg

[matthmal]

Re: Benq Q7T3 - No Power

will do and will let you know

[matthmal]

Re: Benq Q7T3 - No Power

So i have removed the following transistors from the board:
- Q805 -> DLOPF
- Q812 -> DLOPF
- Q815 -> C5707
- Q816 -> C5707
- Q809 -> C5707
- Q808 -> C5707

they are all blown as when testing them the results where all 1 (meaning out of range)

I also tested the following diodes off the board, POWER OFF 2000ohms:
- D601 -> 530 on one side and 1 (meaning out of range) on the other side
- D602 -> 588 on one side and 1 (meaning out of range) on the other side

[matthmal]

Re: Benq Q7T3 - No Power

You should test these transistors out off the board, and try using ECB instead as shown here:
http://s807.photobucket.com/albums/y...t=DSCF0766.jpg

i tested the transistors as you told me... the ECB mode all results returned the same -> 1 (out of range)

[matthmal]

Re: Benq Q7T3 - No Power

any sort of feedback please?

[budm]

Re: Benq Q7T3 - No Power

"all results returned the same -> 1 (out of range)" That means the resistance is too high for the meter to display, I expect to see 200 Ohms or less for the bad transistors. So your C5707 are OK.

"- Q805 -> DLOPF
- Q812 -> DLOPF"
Not sure what the 'DLOPF' is.

[Rtech]

Re: Benq Q7T3 - No Power

"all results returned the same -> 1 (out of range)" That means the resistance is too high for the meter to display, I expect to see 200 Ohms or less for the bad transistors. So your C5707 are OK.

"- Q805 -> DLOPF
- Q812 -> DLOPF"
Not sure what the 'DLOPF' is.

Presume he means STD10PF06...'P' Channel ,used instead of the FU9024N.

[matthmal]

Re: Benq Q7T3 - No Power

mmmm ok.... then what else could have gone wrong?