I-INC TW191d - No Image from Computer after Capacitor Replacement

[Rolin]

Guys, I have a I-INC tw191d Monitor that someone gave to me because it had problems - dim display, won't come out of standby, etc - getting worse. I took it apart and found 5 leaking caps - 3 470uf 25V, and 2 1000uf 10V. I replaced those, and the monitor powers up, shows the test "No Signal" message. Looks good, so I reassembled and tested on a computer - no image from the computer. I tested with another cable - fails.

So the monitor works as far as displaying the test "No Signal" message, but won't display any computer image.

Could one of the caps I replaced caused this issue? I'm well versed in soldering, so I can't believe I damaged anything else on the board, but I suppose anything is possible - but nothing that looks obvious visually.

One thing I should mention - the 470uf Caps are a little shorter than the original - 12mm instead of I think 14 or 15mm, but that shouldn't matter. Other than that, I have no idea what happend.

Can anyone help?

[1supertech]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

Test the mainboard for bad caps

[Rolin]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

Looks like it's the same model as the Princeton VL1919 if that helps.

[Rolin]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

I tested the main power supply/inverter board for output. The pins that lead to the logic board (I think that's what it's called) are marked so I metered them.

12V = 11.87V, +5V= 5.23V, and adj = 0V

Not sure what the "adj" should be when it's not connected to the logic board or anything else, but I suspect it should be 0V when testing this board alone.

My gut tells me it's somewhere on the logic board, since that's where the vga connectors are, and the power supply looks like it's supplying proper voltages. Although I should find a way to test the "adj" voltage I suppose.

Can anyone give me a nudge in the right direction...? Does it look like a problem on the logic board?

[sabre504]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

Have you checked the voltage regulators on the main board ?

[budm]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

'ADJ' is the backlights brightness adjustment signal for the inverter circuit. You have main board problem, check the voltage regulators as suggested.

[Rolin]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

Thanks so much guys!

I only see 1 voltage regulator on the logic board (or mainboard). Tested as follows:

Chip type is 1117
pin 1 = 2.1V
Pin 2 = 3.34V
Pin 3 = 4.51V

According to the spec sheet - this is a variable voltage regulator and states Pin 1 is adj, pin 2 is output, and pin 3 is input.

Looks like Pin 3 is low - Shouldn't it be 5V? So does that mean theres another problem on the board feeding this regulator? According to your example in your tutorial - the 1117 chip adjusts the output by 1.25V, so pin 1 is 2.1V plus- 1.25 is 3.35V - appears to be within spec. So does the regulator test OK? 1supertech was most likely on the right track with a possiblity of a faulty cap?

[budm]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

Adj pi + 1.25v vref = output voltage, so 2.1v+1.25 = 3.35V, it is OK, but the 5V is low, you should check the caps for input and the output of this regulator. you can solder in the new cap in parallel with the old one just to see. What kind of meter do you have, does it have frequency counter function?

[Rolin]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

I have a craftsman 82139 meter. I see a "FREQ %duty" on the dial, but have no idea how to use it or if it's what you're looking for.

[budm]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

Set it to freq, black probe on the chassis, red probe on the input pin, then the output pin, tell me what you see.
https://www.badcaps.net/forum/showthread.php?t=31410

I do not know the spec of your meter so it may not give me what I need.

[Rolin]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

I set it to FREQ, and tested each pin on the regulator. I get a number but it quickly jumps to 0. Does this on each pin. And each time I put the probe on the pin, it's a different number every time but always drops to 0 within a couple of seconds. Doesn't appear it's giving any consistant numbers.

[budm]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

You meter may not have enough bandwidth like my Fluke. At this point I would solder in the caps to the input and the output and see if the 5v will come up. There should be 5V power supply pin on this logic board, see if it is also low.

[Rolin]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

I checked voltages at various places on the board around that voltage regulator and found D21 is where it drops from 5V to 4.5V. One side is 5V, and the other side is 4.5V.

D21 is located right above the caps on the far left near the voltage regulator. D21, I assume it's some sort of Diode? Is this where the problem is?

[budm]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

That is correct voltage then, so it looks like the regulator input pin is fed through the diode which will make the output of the diode to be 0.6V less due to the Vf of the Diode.

[Rolin]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

Not sure what I should do next. I think I understood that the diode voltages are correct, which feeds the voltage regulator at 4.5V. This is correct then? So it's not the voltage regulator or the diode at this point.

Just to recap the problem: The monitor shows a display of menus etc OK, but will not show an image from the computer - it's just blank. Acts like a faulty cable, but I tried another cable. Any ideas?

[budm]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

Yes, that is correct, it is being fed by 4.5V due to the voltage drops of 0.6V on the Diode. I am not sure where to look next. It reminds me of the SAMSUNG monitor problem due to corrupt EEPROM.

[Rolin]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

The person who gave me the monitor said it's becomming dimmer and sometimes won't wake up. That would certainly fall in line with the failing caps in the power supply. But she never said anything about having a blank picture - unless that's what she meant by not waking up. I suppose it's possible I damaged something, somehow?? I didn't power up the monitor to a computer before I took it apart so don't know if it's a new problem or not. Very stange...

[momaka]

Re: I-INC TW191d - No Image from Computer after Capacitor Replacement

Seems like you forgot to change one capacitor on the power supply (top right corner of second picture in 1st post). Looks like a CapXon. It may not be the issue, but it will fail if it's a CapXon, and no telling if that will affect the monitor or not.

If you're ordering caps again, you might as well get caps for the video/logic board too. The ones in the bottom right corner are for the monitor speakers/amplifier, so they aren't important, but the other ones on the video board - particularly the bigger ones are and should be changed.