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Old 01-05-2018, 07:24 AM   #1
freedomlives
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Default Hp lw1965

This display has the similar problem like another post on this forum for the same model of display-- backlight on, but LCD black. Following through that post lead me to take out the LCD panel and check it. Only it seems that HP changed LCD panel providers or Samsung the maker of the panel changed the driver circuit, because what I have with the Samsung LTM190EP01 panel is a different set of components. But anyway, I found that the one fuse on the driver board (F1) is blown. I didn't find any shorted capacitors, and between the terminals of the two voltage regulators (LD33 and LD18) there is some resistance ~2k on one, 500 on another.
I guess the best thing is to desolder them and test?

I noticed some marks inside identifying which wires go where, so I'm not the first person to have opened up the display it seems, and as I just purchased it for 10 ("display is dim" the seller said), I don't want to put too much time in, but if there's an easy fix, that would be cool.
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Last edited by freedomlives; 01-05-2018 at 08:03 AM..
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Old 01-05-2018, 08:03 AM   #2
freedomlives
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Default Re: Hp lw1965

I couldn't get the two regulators unsoldered, so I just applied 5V to the input of the first, and got 3.3V out on it, 1.8V out on the next. So regulators don't seem to be bad.
Is it ever possible that just "sh*t happens" and replacing the blown fuse things will work again?
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Old 01-05-2018, 08:55 AM   #3
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Default Re: Hp lw1965

I got impatient, and just shorted out the fuse. so far its working . :-)
If it fails, then at least it has a nice adjustable stand with a VESA mount. I guess I'll order some fuses off ebay though if it continues working the rest of the day.
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Old 01-05-2018, 10:22 AM   #4
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Default Re: Hp lw1965

Quote:
Originally Posted by freedomlives View Post
Only it seems that HP changed LCD panel providers or Samsung the maker of the panel changed the driver circuit, because what I have with the Samsung LTM190EP01 panel is a different set of components. But anyway, I found that the one fuse on the driver board (F1) is blown.
The picture you posted is of the T-con board (the board that is attached to the LCD TFT.) Just stating this for clarity.

Quote:
Originally Posted by freedomlives View Post
Is it ever possible that just "sh*t happens" and replacing the blown fuse things will work again?
Rarely, but YES.

Most blown T-con fuses are usually a result of shorted ceramic capacitors on the main and secondary boosted voltage rails. That said, I've seen two cases of blown fuses with no problem (both of them were from badcaps.net members).

Quote:
Originally Posted by freedomlives View Post
I got impatient, and just shorted out the fuse. so far its working . :-)
If it fails, then at least it has a nice adjustable stand with a VESA mount. I guess I'll order some fuses off ebay though if it continues working the rest of the day.
Nice.

For the future suggestion, though - do NOT short fuses directly - ever! This can cause more damage (and sometimes make the device unrepairable). Not to mention that doing this on a mains/high-power fuse, that can be a fire hazard.

If you don't have the right type of fuse, it's OKAY to use a lower-rated fuse. In this particular case with your T-con, you could have soldered some wires to a regular standard 5x20 mm fuse and soldered the other ends of the wires to the T-con board. I do that all the time when I don't have the right type of SMD fuse.

Anyways, congrats on the repair!
And yes, definitely get the correct replacement fuse.

Last edited by momaka; 01-05-2018 at 10:23 AM..
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Old 01-05-2018, 10:37 AM   #5
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Default Re: Hp lw1965

Thanks!

That's a good idea with the larger fuse. I don't have any SMD fuses. I just placed the order on ebay for 20 for $2 from China. The electronics distributor here wants 0,60€ plus there would be shipping at least 4€ and I don't have anything else I particularly need right now.

For now anyway the monitor isn't going to be used. I had gotten it when the L2045w display started doing the 2-seconds off deal, hoping that the seller was honest about the display working but being dim (my wife picked it up in the city and there was no chance to test it). The L2045w is the second display on my PC. I'd like to have three, but I was having issues using the internal videocard with the dual output video card, so for now this 1965 has no use.

Here's a question-- on the L2045w power supply there were a bunch of places marked CPx (where x is an integer) with a diamond shape around it. One of these was shorted with a blob of solder that had a lot of flux around it-- and honestly, it was another act of desperation that after checking for obvious badcaps and failed transistors, I just removed the solder blob, as the flux around it made me feel like it wasn't original, and the display works again. Maybe it was just some other luck-- that display is also used, and at first it was randomly turning off after hours of use, then more frequently, then I set brightness to the lowest setting and for a few more months it was fine, then the 2-seconds and off routine.

Anyway, right now, I've got a second display and a backup, which is good, because I've got a lot of work on the computer for the winter months after spending all of the fall doing home improvement / reconstruction work.
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Old 01-05-2018, 10:41 AM   #6
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Default Re: Hp lw1965

the L2045w power supply PCB with one of these CPx marks circled in red.
Check point? Control point?
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Old 01-09-2018, 07:47 AM   #7
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Default Re: Hp lw1965

Hmmm. I have seen those marks before, but never paid much attention to them.

It is possible that the solder blob was done at the factory to correct for some issue or "fine tune" something. But it's also possible that someone played with the monitor when they didn't know what they were doing.

You'd have to track what that CPx point goes to and try to figure out why it was bridged. The one you show in your picture appear to be close to what seems like the CCFL inverter controller. It could be that this point disables any protections when it's bridged. Or it could be something else. Best way is to find the datasheet for the controller and look inside its Application schematic, then compare to the circuit in your monitor, then try to figure out what those points do. It's a bit involved, but that's the best you can do without a full circuit schematic of the monitor (and often, you won't find one).
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Old 01-15-2018, 02:29 AM   #8
freedomlives
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Default Re: Hp lw1965

Well, the fix on the 2045 worked for a week. Now this morning after the outside temperature plunged to -7C and I hadn't been in my office a few days, so its cold too, its again doing the two seconds on, then off. I guess ambient temperature would affect marginal capacitors?
I ordered an ESR meter off eBay a week or two ago, so I guess I can go through those when it gets here.
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Old 01-15-2018, 05:23 AM   #9
freedomlives
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Default Re: Hp lw1965

Hmm... and now the 2045 is working again, after I heated up the office. I guess I don't like working in the cold, so neither does the backlight ;-)

The LW1965-- I'm playing it safe and waiting for the fuses to come. I bet by next week it will be here.
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Old 01-19-2018, 10:11 AM   #10
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Default Re: Hp lw1965

Time to have a look at the caps on the power supply too, then. Those could be the reason for the monitor not wanting to start in the cold.
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