Viewsonic 2262wm-2 (VVS12132) 2 sec. to black

[julien419]

Hello,

I am currently in the middle of my second monitor backlight/inverter repair (the first was a dell 2005fpw that just had some bad caps). My university was throwing out a viewsonic monitor so I decided to grab it from the e-waste bin and try to revive it. It has the typical issue of the backlight coming on for a few seconds and then shutting off.

I have a DMM and an LCR meter and I started by replacing C918 and C917 (center top in the third picture, center left in the first two) as the tops were physically bulging. I then measured the remaining ones and if they gave funny values, desoldered them and remeasured. None of them were terrible, but I replaced a few that I had equivalent caps for with slightly better DFs. Problem still persisted.

I next tried measuring the transformers as indicated in the sticky thread. The two transformers on the side of the board near the lamp connectors behaved as expected. The large square transformer in the center of the board (T901) gave me interesting results. Between the four top pins, less than 0.1 ohm was measured (circled orange). For the bottom set of pins, however, it seemed like there were two sides (circled yellow). The two groups had negligible resistance between the two pins in the group and OL between the two groups. My guess is that there are just two pins connected to the same side of the winding in the transformer, but I thought I'd throw it in to get any other opinions on it.

I don't have a spare ccfl lying around, so the next step that's easy for me to do would be to open up the LCD unit itself to try to get a peek at the backlights for any signs of a burnt out bulb. I'm not sure this will be it, though, as I didn't notice unevenness in the backlight for the split seconds it was on. As far as testing diodes and transistors, I could just go to town on the board and start trying to test everything, but I figured I'd post on here and see if anyone had any better ideas first.

Thanks in advance for any advice
Jackson

[budm]

Re: Viewsonic 2262wm-2 (VVS12132) 2 sec. to black

You can build two test lamps to help you reduce the troubleshooting times to find out if you have lamps or board problem.
I would have at least replace all the filter caps in the secondary side.
https://www.badcaps.net/forum/showthread.php?t=19987

[julien419]

Re: Viewsonic 2262wm-2 (VVS12132) 2 sec. to black

Thanks for pointing me towards that sticky thread. I read it in the past but it clearly didn't stick enough. I'll have to find a couple sacrificial CFLs to solder to the board.

This may be a silly question, but when you talk about the secondary side are you taking the primary side as the side where line voltage comes in? If so, I've replaced almost all of the caps on the left side of the board (the brownish ones are original, all the blacks are ones I've replaced with the exception of the large 450V cap). The only three remaining are two 16V 1mF caps and one 25V 1mF cap. I measured the 16V caps right after I replaced the two bulging 16V 470uF caps as I expected them to be bad too but their values didn't seem out of tolerance when I measured them. Nevertheless, I could replace them with 25V and 50V 1mF caps just to see what happens (I don't have 16V 1mF caps and the 25V 1mF caps I have measured a slightly higher ESR than the 25V cap that's in the board already). It would certainly be an easy thing to rule out for sure.

[julien419]

Re: Viewsonic 2262wm-2 (VVS12132) 2 sec. to black

I sawed open a CFL as suggested by budm and soldered it to each of the four connectors in turn. It sputtered/hissed and the CFL lit to varying degrees in the different positions but the backlight never stayed on. I just now noticed that you specifically mentioned two test lamps. Most other places on the site mention using only one. Do I need two since there are two transformers on my power board? Is there a certain configuration I should solder them on in while testing?

I also replaced one of the 50V 22uF caps left on the board with the best one I could find in a bin in the lab (still has about an ohm of ESR, but down from 2 ohms). The only original caps on the board still left are the 450V cap in the middle and the other 50V 22uF.

[budm]

Re: Viewsonic 2262wm-2 (VVS12132) 2 sec. to black

Your monitor has 4 lamps, it will only take one bad lamp to trip the protection circuit.
Please also check the Inverter transformers high Voltage winding resistance between pin 7 and pin 8 (you can see the pin's label on the bottom side of the board).
Also need the P/N of MOSFETs Q804, Q809 on the bottom side of the board in the inverter section.

[julien419]

Re: Viewsonic 2262wm-2 (VVS12132) 2 sec. to black

Pin 7-8 resistance for both transformers is between 450 and 460 ohms.

Q804 (and 809) are Nikos P5506HVG (). Q808 is labeled RKM. I don't see any other text on it (at least not with my eye - I can look at it under a microscope if there should be more text in smaller font that I can't see).

[budm]

Re: Viewsonic 2262wm-2 (VVS12132) 2 sec. to black

OK, the winding resistances are good.
It is Dual MOSFET (Q804, 809), you can check the resistance between the S pin and the D pin to see what you get.
BTW, sorry about the typo, it should be Q809 (not Q808) in post 5, I made the correction.

[julien419]

Re: Viewsonic 2262wm-2 (VVS12132) 2 sec. to black

Thanks for attaching the pdf. I should have done that rather than link to it. I'm getting 3+ Mohms between the S/D contacts of all 4 NMOSFETs on those chips.

[budm]

Re: Viewsonic 2262wm-2 (VVS12132) 2 sec. to black

Good, so they are not shorted, the inverter transformers are good based on your resistance readings, so continue on using two lamps per set of output of each inverter transformer.

[julien419]

Re: Viewsonic 2262wm-2 (VVS12132) 2 sec. to black

Alright. I'll scrounge up another CFL this weekend and give it a try with using only two of the original bulbs at a time and report back my findings. Thanks for your guidance.

[julien419]

Re: Viewsonic 2262wm-2 (VVS12132) 2 sec. to black

With two CFL bulbs I was able to get the monitor to stay lit. Tore it down further and extracted the culprit bulbs. Now on to finding and ordering some replacements!

[budm]

Re: Viewsonic 2262wm-2 (VVS12132) 2 sec. to black

I am glad the CCFL's method works out for you to be able to find the cause of the problem. It saves so much time to find out if you have lamp/s or board problem.

http://www.ccflwarehouse.com/