HP-L1506 keeps blowing internal fuse

[Agent24]

Re: HP-L1506 keeps blowing internal fuse

Did you check\swap the big grey capacitor between the 2SC5707s?

Have you checked the inverter transformers winding resistance, compared to each other and to one of the working boards?

Have you tried swapping the SMPS controller IC601 with one from a working board?

[techfixit]

Re: HP-L1506 keeps blowing internal fuse

You could swap them with the good pair to be sure.

It happens rarely, but sometimes a part can test OK, but be just bad enough to fail under operation.

I just tried the pair from the fully working board in the non working board and got the same result as before.. will power on for a second or 2 then restart

[Agent24]

Re: HP-L1506 keeps blowing internal fuse

You could swap them with the good pair to be sure.

It happens rarely, but sometimes a part can test OK, but be just bad enough to fail under operation.

[techfixit]

Re: HP-L1506 keeps blowing internal fuse

Ok so i tested both transistors out of circuit and compared them to a pair from a working board and the results are identical so i guess there working fine.

[techfixit]

Re: HP-L1506 keeps blowing internal fuse

Cheers guys, Will do as instructed and report back with the results It'll have to wait until tomorrow unfortunately as it's 2:40am here.... ZZZZZZZZZZZZzzzzzzzzzzzzzzzz

[stj]

Re: HP-L1506 keeps blowing internal fuse

test off the board.

[budm]

Re: HP-L1506 keeps blowing internal fuse

"Red-B + Black-C=.468k Black-E= .148k" 148 Ohms that does not look right. Since you have the other board you can do comparison reading or take it out and test again off the board. I use Ohm mode to check for resistance reading since bad semiconductor will not act like diode any more (conducts in both direction).
You can also take those two transistors and see if it will still go into shutdown, you just will not have backlights.

[techfixit]

Re: HP-L1506 keeps blowing internal fuse

Sorry that was a typo "I" should have been "E" for emitter. The first test was done in diode mode so i presume the figure is voltage drop?

Black-B + Red-C=410, Red-E=210
Red-B + Black-C=410, Black-E=210

Here's what i get testing the resistance

Black-B + Red-C= .468k, Red-E= 3.08k
Red-B + Black-C=.468k Black-E= .148k max initially then slowly decreases

[budm]

Re: HP-L1506 keeps blowing internal fuse

"Black-B + Red-I=410, Red-E=210
Red-B + Black-I=410, Black-E=210"
I do not understand what the readings are, the transistor has EMITTER, COLLECTOR, and BASE.
Also 410 Ohms, K Ohms, or M Ohms, same for the 210.
http://s807.photobucket.com/user/bud...tml?sort=3&o=2

[techfixit]

Re: HP-L1506 keeps blowing internal fuse

So you see the screen lights up for second and then the power LED goes off?
Did you check the transistors for the inverter circuit Q714, 715?

I get picture (test image) for about a second then the display shuts down, The status light also changes from green to orange just as the screen powers off. It continues this cycle until i press the on/off button or unplug the power cable. I've tried unplugging all connections attached to the power supply board but it still does the same thing.

Both transistors are C5707. Testing them in circuit i get:
Black-B + Red-C=410, Red-E=210
Red-B + Black-C=410, Black-E=210

Is that a good transistor or should i remove and test out of circuit?

[budm]

Re: HP-L1506 keeps blowing internal fuse

Excuse my ignorance but what capacitor would that be? Can you highlight it on one of my photos?

Two small lytics caps in the primary side next to small 4-pin Opto isolator and ref diode IC702.

[techfixit]

Re: HP-L1506 keeps blowing internal fuse

Did you check the SMPS controller's Vcc supply filtering capacitor? If that is bad you may get those symptoms.

Excuse my ignorance but what capacitor would that be? Can you highlight it on one of my photos?

[budm]

Re: HP-L1506 keeps blowing internal fuse

Some good news to report. I changed the failed Mosfets on all 3 boards and 2 of the monitors are working perfectly now

The third monitor is turning on but then immediately switches off and restarts as soon as the test image appears. I've got 318v at the main filter cap and i've checked all the other filter caps with an ESR meter and all of those tested good.

Has anyone got any suggestions?

So you see the screen lights up for second and then the power LED goes off?
Did you check the transistors for the inverter circuit Q714, 715?

[Agent24]

Re: HP-L1506 keeps blowing internal fuse

The third monitor is turning on but then immediately switches off and restarts as soon as the test image appears. I've got 318v at the main filter cap and i've checked all the other filter caps with an ESR meter and all of those tested good.

Did you check the SMPS controller's Vcc supply filtering capacitor? If that is bad you may get those symptoms.

[techfixit]

Re: HP-L1506 keeps blowing internal fuse

how about a foto of the board.

It's the same board in the previous pics i posted

[stj]

Re: HP-L1506 keeps blowing internal fuse

how about a foto of the board.

[techfixit]

Re: HP-L1506 keeps blowing internal fuse

try swapping the boards around to narrow it down.
see if all the power boards are good.

Sorry should have mentioned i tested the non working board with all 3 lcd's and same result

[stj]

Re: HP-L1506 keeps blowing internal fuse

try swapping the boards around to narrow it down.
see if all the power boards are good.

[techfixit]

Re: HP-L1506 keeps blowing internal fuse

Some good news to report. I changed the failed Mosfets on all 3 boards and 2 of the monitors are working perfectly now

The third monitor is turning on but then immediately switches off and restarts as soon as the test image appears. I've got 318v at the main filter cap and i've checked all the other filter caps with an ESR meter and all of those tested good.

Has anyone got any suggestions?

[Agent24]

Re: HP-L1506 keeps blowing internal fuse

Can you elaborate on snubber components? Would the mosfet failing have caused the main filter cap to dry out or did the mosfet fail because the filter cap did? Sorry about the pics.. I'll upload directly from now on

The snubber components will be in parallel with the primary transformer winding the FET switches. Look for a highspeed diode, high voltage capacitor (1kV or more) and maybe some resistor(s).

The attached BenQ schematic is very similar to yours. D603, C603 and R603 make the snubber network. In your case it looks like C603 is actually C614.

Check those components for open circuit.

It's very possible that a failed primary capacitor will blow the FET. The other way around is not so likely.

IC601 part number is:

1200AP40
CPDM
0601G

I found and attached the datasheet. Make sure you get the right version (ends in 40) otherwise it will be the wrong frequency.