HP L1925 LCD Video Input Logic Board won't accept signal

[maverick530]

I have an HP L1925 LCD Video Input Logic Board that powers on, and I get the standard "check signal cable" display, but as soon as I plug in a source to either the DVI or Analog 15-Pin VGA, it immediately says "no signal" and places the monitor into standby. I've tried all different resolutions and cable types, but to no avail.

What could be the cause of the board not accepting a signal? Could there be a blown capacitor somewhere? What else could I test?

[EGuevarae]

Re: HP L1925 LCD Video Input Logic Board won't accept signal

I can only figure a TAICON from the picture. Can you give info on the other caps (cap, Voltage, brand)?

[PCBONEZ]

Re: HP L1925 LCD Video Input Logic Board won't accept signal

DVI and VGA are not hot-swap.
Turn it off when attaching cables.

[maverick530]

Re: HP L1925 LCD Video Input Logic Board won't accept signal

Once plugged in to inputs, I've tried cycling the power off and then on again, so that the cables are already plugged in, but as soon as this board detects a signal, it shuts down. I've never seen anything like it.

[maverick530]

Re: HP L1925 LCD Video Input Logic Board won't accept signal

The smaller caps around the DVI/VGA inputs are black TEAPO 12/02 16v 10uF SS 105 degrees C.

Slightly larger brown ones are: TAICON 16v 100uF 0304(M) 105 deg C (VT).

There are also some larger 470uF TAICON, and the one big green one is TAICON as well.

[maverick530]

Re: HP L1925 LCD Video Input Logic Board won't accept signal

I wonder if it's the TEAPOs that are the culprits since I have another of the same boards that is 100% TAICON caps (exhibits different problem).

[EGuevarae]

Re: HP L1925 LCD Video Input Logic Board won't accept signal

The smaller caps around the DVI/VGA inputs are black TEAPO 12/02 16v 10uF SS 105 degrees C.

Slightly larger brown ones are: TAICON 16v 100uF 0304(M) 105 deg C (VT).

There are also some larger 470uF TAICON, and the one big green one is TAICON as well.

Teapo

Replace the 470uf ones & test. Then if not working, the 100uf and then the smaller (10uf) ones.
I've seen suggested the use of Panasonic FC series (Digikey) more than once around here. I ordered some of them, but in the meantime I've used Rubycons that I got from dead boards and so far so good....

[maverick530]

Re: HP L1925 LCD Video Input Logic Board won't accept signal

I finally got around to testing this board with a digital multimeter (DMM). On Ohm Resistence test (setting 2000), I saw that the following 4 capacitors (circled in attachments) registered shorted (0 value basically): 2 100uF and 2 10uF. *I tested them on-board*--haven't removed them yet.

My question is, if I replace these 4, do you think it'll work? Do Caps normally go bad around each other like this? How sure can I be that it is the caps, and not some other component on the board?

[EGuevarae]

Re: HP L1925 LCD Video Input Logic Board won't accept signal

I finally got around to testing this board with a digital multimeter (DMM). On Ohm Resistence test (setting 2000), I saw that the following 4 capacitors (circled in attachments) registered shorted (0 value basically): 2 100uF and 2 10uF. *I tested them on-board*--haven't removed them yet.

My question is, if I replace these 4, do you think it'll work? Do Caps normally go bad around each other like this? How sure can I be that it is the caps, and not some other component on the board?

Have you tested the same caps on the other board?

[maverick530]

Re: HP L1925 LCD Video Input Logic Board won't accept signal

Yes, I actually have 3 of these boards--all with varying problems. The other 2 check out fine on these same contacts. In other words, the others do not show a short for these caps.

[EGuevarae]

Re: HP L1925 LCD Video Input Logic Board won't accept signal

Change them all. Teapos / Taicons give problems. You can start changing those at the signal input area, and then if it starts working properly, go ahead and change all the others now to prevent further problems.

[maverick530]

Re: HP L1925 LCD Video Input Logic Board won't accept signal

Where's the best place to buy these caps online? What brand should I get? Thanks in advance,

[EGuevarae]

Re: HP L1925 LCD Video Input Logic Board won't accept signal

Panasonic FC series have been suggested more than once around here.
Reliable caps.
You can get them from Digikey.com

[maverick530]

Re: HP L1925 LCD Video Input Logic Board won't accept signal

Ok, I just replaced the 4 suspected "bad" caps, and each circled tap still registers as shorted. I tested the "bad" caps once out, and they all seem to hold charges. So, it turns out that it wasn't a cap problem at all, and I'm still left with a bad monitor that won't accept a signal. What else can I try?