HP F1523 - 2 secs display then darkness

[Bobdee]

Re: HP F1523 - 2 secs display then darkness

Hellow again
Much better pictures, but theres no inverter fuse, I cant see any problems, but some of these guys can spot a needle in a haystack, and krankshafts data wil help, will keep following with intrest, Good Luck
bob

[PCBONEZ]

Re: HP F1523 - 2 secs display then darkness

That's the only fuse the first Viewsonic I did had on it too.

Circled transistor probably isn't too happy in so far as heat dissipation living in that pile of goop.

.

[EGuevarae]

Re: HP F1523 - 2 secs display then darkness

Hellow again
Much better pictures, but theres no inverter fuse, I cant see any problems, but some of these guys can spot a needle in a haystack, and krankshafts data wil help, will keep following with interest, Good Luck
bob

I couldn't find a fuse either (in the pics). And yes, Krankshaft is referring to those 8 pin ICs. Getting the data can lead to a test method to see if they are bad.

[anno]

Re: HP F1523 - 2 secs display then darkness

possible I102 and I103 are shorted (or one of them). Inverter goes in protection and shuts off.

a simple way to test them is with the 'fingerproof'. power the monitor on several times , then power off and check with finger if one of them is getting very hot (the 8 pins ic I102 and I103). That one is shorted/defect. But be carefull in inverter area with power on , please!

I don`t see a fuse eather.

also it`s possible that there is a bad ccfl lamp. the inverter shuts off, goes in protection. Try another pair of ccfl lamps if you have.

[stroogly]

Re: HP F1523 - 2 secs display then darkness

Before you replace any more stuff, you might try plugging in 2 known good backlight lamps and seeing if they stay on. Careful with the high voltage.

Most inverter circuits have a current sense that turns off the inverter if either lamp is open.

Also, if you are still having a flash symptom, it is not a fuse so you needn't look for one. If the fuse blows, the inverter won't come on even for a second.

Hope that helps-

-Michael

[kikkoman]

Re: HP F1523 - 2 secs display then darkness

i found a service manual for the f1523... unfortunately the schematics part is missing. BUT it says the IC it uses is a OZ960 (datasheet is attached), and that's consistent with your picture.

i strongly suspect it's the open lamp protection. an open fuse or shorted FETs wouldn't power the thing for 2 seconds.

pin 9 (FB) should normally get a current from the low side of one of the lamps. it probably doesn't because one or several of the transistors (Q105, Q106 and the gooey one) are fried and pull FB down.
the datasheet isn't very clear about this but i'm pretty sure that the protection kicks in when the FB current isn't high enough after the soft start and/or ignition phase.
you could either try to verify that by upping the value of C103 (let's say double) which should prolong the soft start phase in which I(fb) is ignored but i'm 99% sure that replacing the three transistors fixes your problem.

can you find out their markings?

[Bobdee]

Re: HP F1523 - 2 secs display then darkness

Hello CariadBach,
Just spotted pins 5+6 on the I101 that KiKKoman mentions, in his posting, are discoloured, I not sure if that says anything.

Also you have not come back on that good bit of info that Anno gave, if I102+I103 are suspect, here is a datasheet for them (I believe) I could not find anywhere to obtain them for you.

http://pdf1.alldatasheet.com/datashe...MD/AOP600.html

bob

[CariadBach]

Re: HP F1523 - 2 secs display then darkness

Hi everyone

Thanks for the new contributions. This forum is seriously impressive.

My apologies but I haven't had a moment to progress this week and unless I get a spare hour or so tomorrow, I probably won't until early next.

I'm not in a position to try alternative lamps, so my plan of attack will be to try Anno's suggestion re - I102/I103 and then digest Kikkoman's and Bobdee's comments.

Its a shame work gets in the way of everything interesting...

[mortod]

Re: HP F1523 - 2 secs display then darkness

Thought I would resurrect this discussion as am investigating the exact same problem.

So far I have removed and tested the 3 transistors, and the two 8 pin ICs previously discussed. They tested OK, and none of the caps look at all bad.

One other thing I noticed was that when I test the inverter board (ie with the case open) with the lcd panel connected to the bulb outputs I can hear a brief and quiet fiz sound, followed by the backlights going out and the led going yellow. But when I did the same test without the board screwed down (ie not earthed), there was no fiz sound and the screen remained lit for a good 20s or so before going off. Does that suggest anything to look for? I'm no expert, but perhaps it does suggest a faulty cap leaking to earth??

[aliasdck]

Re: HP F1523 - 2 secs display then darkness

One other thing I noticed was that when I test the inverter board (ie with the case open) with the lcd panel connected to the bulb outputs I can hear a brief and quiet fiz sound, followed by the backlights going out and the led going yellow. But when I did the same test without the board screwed down (ie not earthed), there was no fiz sound and the screen remained lit for a good 20s or so before going off. Does that suggest anything to look for? I'm no expert, but perhaps it does suggest a faulty cap leaking to earth??

I am no means an expert here but I've run into something like this before. Look very closely around the lamp connectors on the circuit board... there could be arching from one of the high voltage lines somewhere. This could leave a small black dot about the size of a pin head at the point where the arching is occuring.

If it is arching, it could be occuring anywhere along the high voltage circuit as well... the transformers, anywhere along the length of the lamp wires (you would need to dissamble the display and pull out the bulbs to see everything), poor connection on one of the bulbs or connectors etc. One way to see where it is occuring may be to try turning on the monitor in a dark room, should be easy to see a purple glow wherever it is occuring.

And we shouldn't rule out the possibility of bad caps. You say they look good, but looks can be very disceiving with caps. If you need help, post good pictures or atleast list which caps you have on the board (manufacturer, series, rating, etc)