Viewsonic VX2433WM - Two Seconds to Black

[sean0118]

Hi everyone,

I have a Viewsonic VX2433WM here with the two seconds to black issue.

It initially had an issue where the 5V rail turned off if the LED/button PCBs were plugged into the controller board. But after cleaning some corrosion between pins of a connector it now turns on, but shuts off two seconds later (Picture looks good when it's on).


When I measure the secondary windings of the HV transformer I get 760ohm on one and 805ohm on the other, difference of ~5.6%. This is with the transformer still in circuit, I removed the capacitor across the winding and there was no change. Next I'll try removing the transformer to test.

Do you guys think the transformer likely has a shorted winding? Anywhere I can buy another one (SPW-139 LSE t10BH)?

[budm]

Re: Viewsonic VX2433WM - Two Seconds to Black

Remove the transformer and look at the bottom side of the transformer to see it i\has any bad sign.

[sean0118]

Re: Viewsonic VX2433WM - Two Seconds to Black

Thanks budm, I removed the transformer, secondary windings still have the same resistance (760ohm & 805ohm), both primary windings are 0ohm.

I couldn't see anything wrong with the bottom of the transformer, no burn marks etc.

I did notice the two ceramic capacitors closest to the transformer were a ddarker shade of blue than the rest, I suspect the transformer runs hot, but maybe that's normal.


edit: Ops, the darker blue ceramic capacitors are actually a different part number to the light blue ones. That probably explains the difference in colour.

[sean0118]

Re: Viewsonic VX2433WM - Two Seconds to Black

The inverter IC is MP1009ES, after checking the datasheet I measured the voltages of Pin 1 OV2 and Pin 16 OV1, both go to slightly above 5V when the backlight comes on, according to the datasheet this means there's a short circuit.


What's strange is it's meant to shutdown once Pin 5 FT reaches 1.2V, however, even with a scope it seems to only reach ~0.5V. Is there something I'm missing here?

[sean0118]

Re: Viewsonic VX2433WM - Two Seconds to Black

Ops!

Nearly everything I wrote in my last post was wrong.

Pin 5 FT (fault) does reach 1.2V!

However, pins OV1 and OV2 are operating correctly, they both have a sine wave with a DC bias of 6V, that's correct operation.

But the current feedback pins LI1 (pin 2) and LI2 (pin 3) both only show a halfwave centered at 0V, according to the datasheet this means that one lamp is open.

Next I'll take the screen apart and check the lamps.

[R_J]

Re: Viewsonic VX2433WM - Two Seconds to Black

If you suspect a lamp issue you can plug in only one at a time and see if it lights for a couple seconds. its a way to confirm the transformer also, if one output is not lighting a lamp, plug the lamp into another output, if it lights there, then the previous output and likely the transformer is bad

[budm]

Re: Viewsonic VX2433WM - Two Seconds to Black

Make a couple test lamps:
https://www.badcaps.net/forum/showth...er+testing+cfl

[sean0118]

Re: Viewsonic VX2433WM - Two Seconds to Black

Thanks guys that was good advice.

The two connectors on one of the secondary windings will light any of the four bulbs. But on the other winding, one connector will light a bulb to 25% brightness while the other connector will not light any of the bulbs.

To test if it was the transformer, I unsoldered it, rotated it 180 degrees and resoldered, the problem then moved to the other two connectors! So transformer related after all...

[sean0118]

Re: Viewsonic VX2433WM - Two Seconds to Black

I'm guessing it's not possible to repair these, but is there a replacment part for this transformer? Is there a generic design that would work? (PN is SPW-139 LSE t10BH)

Otherwise I might just keep the boards and panel as spare parts and recycle the rest. I already broke the bezel taking it apart.

[R_J]

Re: Viewsonic VX2433WM - Two Seconds to Black

The schematic shows the inverter transformer (T501) as EEL-22 but the power supply looks slightly different. Are there any numbers on the yellow band around the transformer?

[sean0118]

Re: Viewsonic VX2433WM - Two Seconds to Black

Well spotted, I have the service manual, but I hadn't thought to check it. I checked the transformer and I couldn't find any more numbers on it, yellow band is blank.

Which part of the schmatic looked different to you? As far as I can tell it matches my board (apart from transformer part number).

[sean0118]

Re: Viewsonic VX2433WM - Two Seconds to Black

I think I might just try replacing it with EEL-22 and see what happens. The overvoltage/current protection circuits should still work, so it should be safe right?

[R_J]

Re: Viewsonic VX2433WM - Two Seconds to Black

I think the eel-22 transformer should work, after a closer look the schematic does seem to match your board, I may have looked at a different schematic and got them mixed up.

[sean0118]

Re: Viewsonic VX2433WM - Two Seconds to Black

Thanks, I bought one on ebay for very cheap, I'll let you know how it goes.

[momaka]

Re: Viewsonic VX2433WM - Two Seconds to Black

There are also cheap 1, 2, and 4-lamp inverter boards on eBay that typically go for $5 from China. Could use one of those to directly get the whole inverter section replaced. But it probably won't end up looking pretty inside and might take more effort than the monitor is worth... but if you like fixing things and time is not an issue, this is just another option.

[sean0118]

Re: Viewsonic VX2433WM - Two Seconds to Black

Update:

Replacing the transformer worked, I'm using the monitor atm, works great.

The trasformer I used was EEL-22, was $4AU on ebay inc. postage for two transformers.


(It took awhile to get this repaired because the transformer got mailed to my old house and I didn't have time to go pick it up.)

[momaka]

Re: Viewsonic VX2433WM - Two Seconds to Black

Good to hear it's working again. Thanks for coming back and updating us on your status.