Viewsonic vx2435wm problems

[savgardns]

Hello guys,
my viewsonic vx2435wm has stopped working. There is backlight but no picture when its turned on, no osd menu, no nothing. Power and inverter board seem to be ok, and on all checkpoints on digital video board that i've tested I get proper voltages. What to check next? Please help
PS here are some pictures of the logic board.

[PlainBill]

Re: Viewsonic vx2435wm problems

Hello guys,
my viewsonic vx2435wm has stopped working. There is backlight but no picture when its turned on, no osd menu, no nothing. Power and inverter board seem to be ok, and on all checkpoints on digital video board that i've tested I get proper voltages. What to check next? Please help
PS here are some pictures of the logic board.

I count 11 LDO regulators (U12 and U12 are examples of one style, U21 and U22 are examples of the other) on this board. Have you verified the output voltage of all of them?

Does the power light work, and respond to the power switch?

What do you see on the screen - black, or solid white?

A picture of the entire back of the monitor would be helpful. I am particularly interested in the destination of the two cables coming off the top of the board.

PlainBill

[savgardns]

Re: Viewsonic vx2435wm problems

Hi PlainBill
power button works, I can turn it on and off. Signal light is blue when it's on, and orange when it doesnt detect video in signal. When i plug in vga cable it goes from orange to blue but few secunds later it goes to orange again. The screen is all black, but i can see that the backlight works.
I dont have any more pictures but i can post some tomorrow of t-con board and everything else you asked for.
Also, i didnt check LDO regulators but voltages that i could check with voltmeter on checkpoints for 1.8, 2.5, 3.3 and 5v are ok all over the board.
Thanx for your quick replys

[PlainBill]

Re: Viewsonic vx2435wm problems

Hi PlainBill
power button works, I can turn it on and off. Signal light is blue when it's on, and orange when it doesnt detect video in signal. When i plug in vga cable it goes from orange to blue but few secunds later it goes to orange again. The screen is all black, but i can see that the backlight works.
I dont have any more pictures but i can post some tomorrow of t-con board and everything else you asked for.
Also, i didnt check LDO regulators but voltages that i could check with voltmeter on checkpoints for 1.8, 2.5, 3.3 and 5v are ok all over the board.
Thanx for your quick replys

With a black screen but backlights on, the symptoms point to a failed IC in the signal processing path. I can't narrow it down from there. It is obvious that there are a LOT of potential suspects.

PlainBill

[savgardns]

Re: Viewsonic vx2435wm problems

ok, but why no OSD menu? is it possible to find somewhere firmware to flash 24c, just to try? i am willing to try everything (or almost everything) to make this thing work again.

[alexanna]

Re: Viewsonic vx2435wm problems

Those 2 flat ribbon cables at the top of the 1St picture go to the LCD panel; it looks like the left one may not installed correctly.

[jetadm123]

Re: Viewsonic vx2435wm problems

Any chance they're using a AAT3522? It's a SOT-23 package.

Disregard. I don't think a reset controller is used on this board.

[PlainBill]

Re: Viewsonic vx2435wm problems

ok, but why no OSD menu? is it possible to find somewhere firmware to flash 24c, just to try? i am willing to try everything (or almost everything) to make this thing work again.

Look at the board. On the upper left corner you have a MST6251. By it's location it's handling the VGA signals from the VGA connector and from the BNC? connectors below them. The 44 pin chip directly above the cable from the power supply obviously handles the control functions. Between the two is a BGA chip that is obviously linked to the MST6251. The NJW1141 is an audio processor. The TVP5147 is a video encoder. The video signals obviously go through the CMO chip. The 44 pin IC surrounded by 4 inductors possibly produces the voltages required by the LCD panel. Either of these last two could CERTAINLY cause the problem you are seeing. The 44 pin control processor (which probably generates the OSD could also.

As far as loading code on a chip, I identify three chips that have the tell-tale dot of paint, indicating they have a custom program.

Other than a misplaced cable, failed regulator, or a non-functioning power supply there is very little chance of repairing this card.

PlainBill

[zamsam]

Re: Viewsonic vx2435wm problems

Hi everyone,

I'm new to this forum, so please be tolerant. I have the same monitor VIEWSONIC VX2435WM, it worked great for awhile, and suddenly stopped working. I read all the info above, and this seems to be the only thread about this monitor on the forum. So keeping it all in one place... Answering above Qs, my monitor doesn't power on anymore, it doesn't react on Power button, and power light is not lit.

Where should I start troubleshooting? Please don't suggest to buy a new one. I'm aware about this option.

[selldoor]

Re: Viewsonic vx2435wm problems

Ok - welcome to the forum.
What experience do you have in electronics?
Do you have a multimeter and a soldering iron and can you use them.
Please provide GOOD CLEAR pictures of the boards in YOUR machine.
We need to be able to read the white part designation numbers on the board.
See my signature below.

[zamsam]

Re: Viewsonic vx2435wm problems

Hi there,

I'm not an expert in electronics by any means, but can do some testing and repairs with a multimeter and soldering iron. This is a review of ViewSonic VX2435wm with detail specs. Attached are my board pictures, can take more. Found also some pic of the power board without heatsinks on the forum.

Where should I start, if you don't mind asking such question?

[selldoor]

Re: Viewsonic vx2435wm problems

OK First find the fuse shown on the last pic then locate the solder joints on the back of your board. Set your meter on ohms200 and with the board not plugged in test the fuse. Should show the same as holding the probes together.

If that is good then see the BIG capacitor CK1 find the solder joints of that on the back of your board. Working on a non conductive surface set your meter on VDC600 and with the mains power applied to the board Very carefully test the
voltage on the Big Cap. DO NOT touch anything else on the board.

Pics are very good thanks

[zamsam]

Re: Viewsonic vx2435wm problems

The fuse FS1 gives continuity sound on the multimeter. The big cap CK1 shows 190V.

[selldoor]

Re: Viewsonic vx2435wm problems

190dvc may not be right but it is a start.
The fuse may give a "beep" sound but is better to get the resistance.
Some meters have been known to beep on a blown fuse. In this case it must be good else there would be no voltage on the big cap.
I am not sure about some of the solder joints on the back of the power supply
is pic of the back of the power supply board your board?

Next thing to test would be the voltage on the "output" sockets, unfortunately they dont look to be labelled so all you can do is set your meter on 200vDC EDIT ( some are labelled on the inverter board end)
and with the monitor all connected up put the black lead on a ground screw
and with the red probe test the voltage at each pin.
Also there is a fuse FS2 on (EDIT) the same board near the "out" socket at the bottom in your picture- a small white one maybe with an "M" or a "w"on it IIRC. With the power off resistance test that. (( also some of the pins look brown on that socket!!)


Also an the left had end of the board in that pic there is FS3 and FS4 so test those as well

Two fuses on the inverter board F1 and F" and also near the white socket from the power supply ther are a couple of jumpers J72 and J73 they are zero ohms resisitors and are sometimes used as fuses to test those as well.

[zamsam]

Re: Viewsonic vx2435wm problems

Yes, the bottom PSB pic is from mine. Sorry to ask a stupid question, but which one is the ground screw on this power board? Is it the one next to red wire, though that screw doesn't look connected in the circuit? Or the opposite screw on the same side, which is connected in the circuit line passing under FS4 fuse, but not through it? Or the screw on the other side with like a ground sign next to it?

Why there's only one red wire on each connector, what the red color marks? If you can refer to component IDs on the PCBs, I could find them more easily.

On PSB other fuses give:
FS2 - 610 Ohm, FS3 - beep, FS4 - 420 Ohm
If I need to replace those, where to find the new ones, and what's the technique to remove them? Any other components I need to check that may have blown up with these fuses?

On the main board I don't see any fuses, unless you can point where they are. On the inverter board ceramic fuses F1 and F2 give beep.

[zamsam]

Re: Viewsonic vx2435wm problems

Voltages on the output sockets with power cable connected:

Connector to the main board from red wire to the left:
0.35, 035, 035, 035, 16.8, 16.8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.35

Connector to the inverter board from red wire to the left:
0.35, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 28, 28, 28, 28, 28

Pressing Power button on the monitor cover doesn't change anything. Couldn't find J72 and J73 jumpers. But I checked all jumpers on the power board, and they all beep. Double checked fuses, and only FS2 gives 300 Ohm now, all other beep.

How to find out, were're the ground pins on the power-to-main board connector?

[selldoor]

Re: Viewsonic vx2435wm problems

Connector to the inverter board from red wire to the left:
0.35, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 28, 28, 28, 28, 28

That cant be correct as it only has 14 pins??

It is helpful if you show what they should be when known

Connector to the inverter board from red wire to the left:
0.35, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 28, 28, 28, 28, 28
PWM NC BL NC ?, ?, G, G, G, G, G, 24, 24, 24, 24, 24

I believe NC will mean not connected and ?? are the extras you have inserted?

J72 is to the right of CN2 and J73 is above it.
Main problem looks to be no 5volts DC

Re Ground on CN3
Not a sure test but if you power off (leave for 10 minutes or so) then
you can test the resistance between the pins that show zero voltage and the ground screw. When your meter beeps does it also show the resistance?
if so please state it.

Fuses - digikey (Order a few )may have them or ebay? usual easy way to affix is to piggyback onto the existing faulty fuse. If you can get them easier
you can use a pico fuse - same voltage and amps - sometimes considered a temporary fix for testing.

I dont have a lot of time to do this at the moment, was hoping someone
else might join us, will try and look in tomorrow.

[zamsam]

Re: Viewsonic vx2435wm problems

My typo, CN2 has 14 pins, you marked 2 extras correctly. No 5VDC for sure.

I can't find J72 and J73 on this board, can you mark them on the PSB picture? Is it possible, your looking at a 2nd version of the same board from another thread, it has the same size, but a different layout and heatsinks with more ribs? There's JP3 next to CN2 and CS21 cap under the heatsink on my PSB, it beeps OK. Don't see any jumpers around CN2 on the bottom side either.

Does the fuse FS2 at 300Ohms sound burned?

I traced Ground pins on CN3 at 7-to-12 from CN2. My meter either beeps on fuses and shows 0, or doesn't beep and shows resistance in Ohms on the same setting, if there's no continuity.

[zamsam]

Re: Viewsonic vx2435wm problems

Strangely, I checked voltages under power on the Power Supply directly again today, and the results are different:

1. Power Supply is connected with both Main and Inverter Boards

Connector to the main board from red wire to the left:
0.15, 015, 015, 015, 16.8, 16.8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.15
Connector to the inverter board from red wire to the left:
0.15, 0, 0, 0, 0, 0, 0, 0, 0, 11.5, 11.5, 11.5, 11.5, 11.5

2. Power Supply is connected with Inverter Board only

Connector to the main board from red wire to the left:
5.8, 5.8, 5.8, 5.8, 16.8, 16.8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.15
Connector to the inverter board from red wire to the left:
0.15, 0, 0, 0, 0, 0, 0, 0, 0, 14.5, 14.5, 14.5, 14.5, 14.5

3. Power Supply is connected with Main Board only

Connector to the main board from red wire to the left:
0.15, 0.15, 0.15, 0.15, 16.8, 16.8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.15
Connector to the inverter board from red wire to the left:
0.15, 0, 0, 0, 0, 0, 0, 0, 0, 28, 28, 28, 28, 28

4. Power Supply is disconnected from both Boards

Connector to the main board from red wire to the left:
5.8, 5.8, 5.8, 5.8, 16.8, 16.8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.15
Connector to the inverter board from red wire to the left:
0.15, 0, 0, 0, 0, 0, 0, 0, 0, 28, 28, 28, 28, 28

Pressing Power Button doesn't change readings. It looks like when connected, voltages on both Main and Inverter boards sharply drop, despite there seems to be almost no load due to no backlight coming on. At least it shows that all fuses are OK?

[selldoor]

Re: Viewsonic vx2435wm problems

Does the fuse FS2 at 300Ohms sound burned?
"in test the fuse. Should show the same as holding the probes together."

So Yes.

Strangely, I checked voltages under power on the Power Supply directly again today, and the results are different:

"and with the monitor all connected up put the black lead on a ground screw
and with the red probe test the voltage at each pin."

That means everything connected and a signal source - PC


I can't find J72 and J73 on this board,

"Two fuses on the inverter board F1 and F2 and also near the white socket from the power supply there are a couple of jumpers J72 and J73"

I have attached a picture with some joints marked that look a bit odd. Often this is due to shadow on the picture but check them out and reflow any that look bad. Reflow = remove most of old solder and add new preferably leaded solder to the joint. What are 1 and 2 and is 3 the heatsink?

Tests FS2 and FS4 again and also check meter batteries are good.

The main board is suspect it appears to not be sending signals to switch everything on ( the power led not coming on is a bad sign ) though if you dont have it all connected up then obviously it cant.
Next tests NO POWER to the boards
Power LED may have failed test it simply by setting your meter on diode mode and placing the probes on each led contact.
On/Off switch - test that it is working - meter on ohms probe on each side of switch.