ViewSonic VA1721WMB

[Mad_Professor]

Found this monitor in the trash.

Typical 2 seconds to black, an image is displayed so nothing wrong with input.

PSU:
6x UCC KY 25V 470uf
1x Elite EG? 35v 220uf
1x Elite EG? 50v 22uf

Question how good is KY?

Unit was MANF. in 06-01-2007

I have Panasonic caps on hand to replace the elites, but need a datasheet to confirm.

[PlainBill]

Re: ViewSonic VA1721WMB

Found this monitor in the trash.

Typical 2 seconds to black, an image is displayed so nothing wrong with input.

PSU:
6x UCC KY 25V 470uf
1x Elite EG? 35v 220uf
1x Elite EG? 50v 22uf

Question how good is KY?

Unit was MANF. in 06-01-2007

I have Panasonic caps on hand to replace the elites, but need a datasheet to confirm.

UCC is pretty good, about as reliable as Panasonic FC. Elite is 'replace on sight' garbage. I'd use Panasonic FC or FM for them.

I wouldn't be surprised if you discover the problem is a bad CCFL, or the wiring for one of the CCFLs.

PlainBill

[Mad_Professor]

Re: ViewSonic VA1721WMB

Replaced elite caps but the monitor still goes to black, the light remains blue.


I shined a light into the lcd to see if it was displaying something but it wasn't.
So what ever it is, it kills power to the lcd driver board and ccfl.

It might be the input board just from how it's wired to the PSU, it got some Chinese looking caps on it. I got to go to work will post pictures later.
Any ideas?

[PlainBill]

Re: ViewSonic VA1721WMB

Replaced elite caps but the monitor still goes to black, the light remains blue.


I shined a light into the lcd to see if it was displaying something but it wasn't.
So what ever it is, it kills power to the lcd driver board and ccfl.

It might be the input board just from how it's wired to the PSU, it got some Chinese looking caps on it. I got to go to work will post pictures later.
Any ideas?

I prefer high resolution (at least 1000 x 1000 pixel) pictures from directly over the top side and bottom side of the power supply and the top side of the signal card. This enables me to follow signal lines, etc.

The cable that links the power supply / inverter has two lines that control the inverter. They are usually labeled BL_ON, BRI, On/Off, etc. The simplest test is to measure the voltage on the BL_ON line. If it changes (drops to 0 volts) when the backlights go off, they are being switched off by the signal card. If it stays at 3.3V, it is 'two seconds to black'.

PlainBill

[Mad_Professor]

Re: ViewSonic VA1721WMB

I tested output of "O/F" with vga input, I read 5v after the monitor went black. It went to 0v when the monitor goes into stand-by if no input is detected.

I tested "dim," it's a constant 5v even when monitor goes to stand-by.

Problem must be on PSU.

What can I test now?

[PlainBill]

Re: ViewSonic VA1721WMB

I tested output of "O/F" with vga input, I read 5v after the monitor went black. It went to 0v when the monitor goes into stand-by if no input is detected.

I tested "dim," it's a constant 5v even when monitor goes to stand-by.

Problem must be on PSU.

What can I test now?

I've defaced one of the pictures you supplied. By the way, this was fun - the pictures are big enough I can do all sorts of things with them.

Do these tests with the power OFF!!

Pin circled in orange: Set your DMM to the 2000 ohms (or 2K ohms) range and measure the resistance from the pin circled in orange to the pins circled in green, orange, and light blue. IF you get a reading on any of them, record that reading.

Now measure from the pin circled in yellow to the same pin that gave the reading. Report the readings.

Spot circled in red. What the heck is that?

PlainBill

[Mad_Professor]

Re: ViewSonic VA1721WMB

I get no readings, tested three times to be sure.

The red thing is a transistor covered in glue looks like from manufacturing, placement number is Q805.

[PlainBill]

Re: ViewSonic VA1721WMB

I get no readings, tested three times to be sure.

The red thing is a transistor covered in glue looks like from manufacturing, placement number is Q805.

OK, that eliminates that shortcut. One possible cause of 'two seconds to black' is a bad transformer. With two or more transformers we can compare and see if one has a lower resistance that the rest, or is open. If the winding was open you wouldn't get any backlights at all, so that is eliminated as the problem.

The two CCFLs are wired in series, so you can't test one without the other present. About the only way to test is to hook up known good CCFLs and see if the problem goes away.

PlainBill

[Mad_Professor]

Re: ViewSonic VA1721WMB

Well, will any CCFL work or does it have to specific size/voltage? I have some cracked laptop screens with CCFL I can harvest for testing, if that will work?

or if you know where to order some bulbs from.

otherwise we need to do something else.

*edit: on a second thought the display was awfully dim.

edit2: But then again it goes to black and nothing is displayed when you shine a light into the screen, like someone kill the power to the unit.

[PlainBill]

Re: ViewSonic VA1721WMB

Well, will any CCFL work or does it have to specific size/voltage? I have some cracked laptop screens with CCFL I can harvest for testing, if that will work?

or if you know where to order some bulbs from.

otherwise we need to do something else.

*edit: on a second thought the display was awfully dim.

edit2: But then again it goes to black and nothing is displayed when you shine a light into the screen, like someone kill the power to the unit.

Within a broad range, any CCFL will work. I've used the CCFLs from a 23" wide screen display to test a 19" narrow screen display.

Shining a light onto the screen is not an absolute test; I haven't had much success with that. The fact is your voltage measurements say the inverter was not switched off. That would indicate it is an inverter / backlight problem, not a signal card problem.

PlainBill