Viewsonic-VX2235wm black screen

[gb77]

i have a viewsonic vx2235 monitor i've been using as a 2nd / extended desktop for my laptop. i replaced all the caps & 2 mosfets (from ebay vendor coreweave - h++p://www.ebay.com/itm/Viewsonic-VX2235wm-REPAIR-KIT-Inverter-LCD-Monitor-/220640945018?pt=LH_DefaultDomain_0&hash=item335f39a37a) on the p/s about 5 months ago, and it worked fine until now. when i turned it off, it was working, the next morning it didnt. other monitors work fine with the laptop. both vga & dvi inputs on the monitor show the same symptoms. the monitor detects the pc (light goes from amber to blue) the panel will flash then stay black. i can see the pc desktop with a flashlight against the screen. when u press buttons to reset the monitor i can see a checkerboard black/white pattern flash briefly. it will flash again if i turn the monitor off and on. while on, i havent been able to cause it to flash again.

in the picture below you can see the darkness around the p/s mosfets which was there before the replacements. both had matching voltages for a quick check of pins 7-9.8v & 8-22.3v. i'm not sure if the discoloration on the upper left corner of the p/s board was there before, or if its new. fuse F102 on the p/s tested good, and F1 on the main, also tests good. i didnt find any cold solder joints, or anything burned or malformed.

the connectors between the 2 boards have the following labels & voltages:
eva 0.56
gnd 0
det 0
+5v 4.99
v_adj 14.05
shut 0
aor+ 2.50
aol+ 2.50

hopefully the info & pics are useful & u can help me with whatever i can try / test to find what's broken - thanks! i took a 2nd pic for a clearer view of the boards

[PlainBill]

Re: Viewsonic-VX2235wm black screen

A little overkill on the information, but that is a LOT better than having to dig it out!!! Thanks!!

The simple explanation is you have 'Two seconds to black'. Possible causes are bad caps, bad CCFL or leads to the CCFLs, bad transformer, bad component in the protection circuitry. Given the caps are 5 months old, we'll mostly ignore them. I say 'mostly' because I suck at identifying caps from the vent pattern. What are the brands and series?

Usually the next step is checking the resistance of the transformer secondaries; I'm going to give that a pass for now because you'd spend an hour scraping off glue.

This next step is easy. Disconnect all the CCFL leads except one. Position everything so you can see the screen. Plug in the monitor and hit the power button until it turns green (or blue). Do you see a flash from the panel? Turn it off, disconnect that CCFL and connect another. Plug it in, hit the power button, etc. Repeat this for all four CCFLs. Do you get a flash on all CCFLs?

If any one CCFL does not give a flash, it is bad. If neither CCFL connected to one transformer gives a flash, the transformer (or the driver) is probably bad. If the CCFLs hooked to one transformer are dimmer, the transformer is almost certainly bad.

PlainBill

[gb77]

Re: Viewsonic-VX2235wm black screen

yup, that step was easy - the results are that the 2 leads from the top of the panel will not give a flash in any of the connections they can reach. the 2 leads from the bottom will give a flash in any connection they can reach with the same intensity (off both transformers). so i guess that meant the top leads or ccfls are both bad. had some fun and disassembled the panel, finding that the top tubes were black on each end, while the bottom tubes are a light gray on the ends. the top tube assy has # 4157112a104 on it (which finds nothing in google). looks like i can get the bulbs from ebay or zlectronic (4 for $26 or less). should i test some more things? or what do u think?

[PlainBill]

Re: Viewsonic-VX2235wm black screen

yup, that step was easy - the results are that the 2 leads from the top of the panel will not give a flash in any of the connections they can reach. the 2 leads from the bottom will give a flash in any connection they can reach with the same intensity (off both transformers). so i guess that meant the top leads or ccfls are both bad. had some fun and disassembled the panel, finding that the top tubes were black on each end, while the bottom tubes are a light gray on the ends. the top tube assy has # 4157112a104 on it (which finds nothing in google). looks like i can get the bulbs from ebay or zlectronic (4 for $26 or less). should i test some more things? or what do u think?

I think you are going to replace CCFLs. Oh, there are a few simple tests, chiefly to determine if there is a broken lead, but at the point you have reached it's virtually certain the upper CCFLs are toast.

PlainBill