ViewSonic VG1930WM

[Diablo_Rojo]

I am trying to res-erect a ViewSonic VG1930WM which shows no signs of life(no LED, no anything). I see no bulging caps. I have verified 14.7v and 5.19v from the power supply. I have attached a page from the LG L192WS manual which apparently uses the same control board(ILIF-020) as the ViewSonic. Pardon my sloppy notes on the schematic. My thoughts are that the voltage regulator U102 is bad. It is an AS1117L-18. I appreciate any input.

[retiredcaps]

Re: ViewSonic VG1930WM

My thoughts are that the voltage regulator U102 is bad. It is an AS1117L-18. I appreciate any input.

U101 should also be outputting 3.3V DC. You can test both U101 and U102 to see if they are shorted. Any resistance reading less than 30 ohms between the pins 1-2, 2-3, and 1-3 suggests a short.

[alexanna]

Re: ViewSonic VG1930WM

So the vin is pin #3 and it has 1.26von it,Is there away you could lift that leg off the pad and see if you read closer to the 5v.?
Al.

[Diablo_Rojo]

Re: ViewSonic VG1930WM

Thank you for the response. I measured U101 and 102 in circuit. The lowest reading I got was about 400 ohms between pins 1-2 on U102.

[Diablo_Rojo]

Re: ViewSonic VG1930WM

Thanks for the idea. I have lifted the leg off the pad for pin 3 on U102. I still get 1.26v on the pad and 4.89v on pin 3 of U101. Maybe C101 is shorting out?

[alexanna]

Re: ViewSonic VG1930WM

I missed the part where you are only reading 1.26v on the output of U101.
Something is taking the voltage low .Is anything hot to the touch
Al.

[shovenose]

Re: ViewSonic VG1930WM

Do you get anything at all in this monitor to show life? Pwr led? 2sec to black?

[alexanna]

Re: ViewSonic VG1930WM

Do you get anything at all in this monitor to show life? Pwr led? 2sec to black?

Well if he has lost the 3.3v and the 1.8v regulators ,I doubt it
Al.

[retiredcaps]

Re: ViewSonic VG1930WM

Thanks for the idea. I have lifted the leg off the pad for pin 3 on U102. I still get 1.26v on the pad and 4.89v on pin 3 of U101. Maybe C101 is shorting out?

My schematic reading skills is presently F-, but I suggest replacing U101 first to see if you get 3.3V DC on VOUT. I can't tell if U102 VIN should be 4.89V DC or the output voltage of U101 VOUT (since the output of U101 VOUT = U102 VIN)? Did I mention my schematic reading skills is F-?

I have a monitor right now with 2 shorted out voltage regulators on the logic card. So it isn't impossible that you have 2 bad voltage regulators? I realize yours are not shorted, but since U101 is outputting low voltage it is bad.

From what I understand of reading PlainBill's posts, a voltage regulator failing low is better than failing high and destroying other components with too much voltage.

[PlainBill]

Re: ViewSonic VG1930WM

There are two problems here. First, the schematic is wrong (or you made a mistake measuring voltages). The schematic shows both U101 and U102 getting power from the 5V supply. That is an unusual arrangement. Given other flaws in the schematic, I suspect it is wrong.

By the voltage measurements, U102 gets it's power from the output of U101. That is a common arrangement.

Either U101 is bad, or something is overloading the output. U102 appears to be good. One trick you can try is to apply 3.3V to the output of U101. If it comes up to 3.3V, the regulator is definitely bad. If it does not rise, something is overloading the 3.3V power rail.

You probably don't have a spare 3.3V power supply sitting around. Use two 'D' cells (flashlight batteries) in series. Fresh alkaline cells will provide about 1.6 volts each.

PlainBill

[Diablo_Rojo]

Re: ViewSonic VG1930WM

Thanks for all the input. I never thought about the schematic being incorrect but it makes perfect sense when I see the input voltage of U102 is the same as U101 output. I was only able to get up to 3.1v with the batteries I have on hand(4 C's in a parallel series combo). When I apply the 3.1v to the output of U101 the voltage falls to 2.6v. Keep in mind that this test was performed with the input leg of U102 still lifted from the pad and the power on. Any advice from here is greatly appreciated.

[PlainBill]

Re: ViewSonic VG1930WM

Thanks for all the input. I never thought about the schematic being incorrect but it makes perfect sense when I see the input voltage of U102 is the same as U101 output. I was only able to get up to 3.1v with the batteries I have on hand(4 C's in a parallel series combo). When I apply the 3.1v to the output of U101 the voltage falls to 2.6v. Keep in mind that this test was performed with the input leg of U102 still lifted from the pad and the power on. Any advice from here is greatly appreciated.

Off the top of my head, the batteries should be able to source over 1 amp in current. Look up the specs of U101. If it's rated for more than 1 amp, U101 is probably bad. Look (CAREFULLY!!!) for an IC getting hot.

PlainBill

[Diablo_Rojo]

Re: ViewSonic VG1930WM

Just wanted to update and give thanks to everybody and especially PlainBill. The VG1930WM is back in service!! I replaced U101 (the AS1117L-33 regulator) and the old girl reciprocated with a blue led then a full screen picture. No problems after several hours. Thanks again.