ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

[Red74Corvette]

What a great forum, thank you to all the participants.

The problem started out with a black screen. The blue led would light when there was a vga signal and the orange when the signal was removed.

I replaced all the caps (except the big one) and the two mosfets. When I tried the monitor after the recap, the led's would not light. I measured 13+ volts going to the logic board, but the 5v was missing. I traced it to a blown f102 fuse. I soldered in a temp fuse to continue testing.

Now when I apply power, both the blue and orange led's stay lit, but no monitor display.

I'm no stranger to the soldering iron, having been a tinkerer for the past 50 years. I confirmed that none of the caps are shorted and to the best of my ability checked there are no solder bridges.

One other observation, not sure if it is important. After powering down and attempting to discharge the caps, the only one with any charge after a minute or so is C200 (220uf 25v) in the very center of the board.

Any thoughts?

[lexwalker]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

Pictures of the boards? Did you check the rectifiers? Also what brand and series/models were the replacement capacitors?

[Red74Corvette]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

Replacement caps are Rubycon YXF. My rectifier "test" was to confirm 166vdc output as specified on one of the posts I saw on this forum.

Anyone have a decent schematic for the dac-19m009 power supply board? I found one for the entire monitor, but it was pretty much unusable.

[budm]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

Check the connector pins between the power supply and the main board, see if you do have Inverter on signal. Is it hook up to running PC?
That cap in the middle is the filter cap for B+ feeding the inverter circuit through that glass fuse.
There are more than 3 versions of this model.
http://s807.photobucket.com/user/bud...?sort=3&page=1
http://s807.photobucket.com/user/bud...?sort=3&page=1
http://s807.photobucket.com/user/bud...?sort=3&page=1

[Mrx3750]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

That power supply looks very familiar.

[sabre504]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

`Have you tested the voltage regulators on the main board ?
A faulty one can cause the monitor to cycle on and off or not start up at all

[lexwalker]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

Replacement caps are Rubycon YXF. My rectifier "test" was to confirm 166vdc output as specified on one of the posts I saw on this forum.

Looks like decent replacements capacitors. The rectifiers I'm talking about are the ones right after the SMPS transformers. If one of them becomes shorted then you'll have AC current going to the Dscaler board instead of DC current.

[kc8adu]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

which would be shunted to ground by a good cap.shorted rectifier=ocp.wont run.

Looks like decent replacements capacitors. The rectifiers I'm talking about are the ones right after the SMPS transformers. If one of them becomes shorted then you'll have AC current going to the Dscaler board instead of DC current.

[lexwalker]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

which would be shunted to ground by a good cap.shorted rectifier=ocp.wont run.

Encountered this several times before on certain power supply boards where the OCP won't kick in even when the one of the rectifiers were shorted. Perhaps a bad capacitor held up the OCP as well...

[Red74Corvette]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

Help me with terminology please. What is SMPS transformer, Dscaler board, OCP?

Regarding voltage regs on the main board, I see two EH16A devices. They both test 5.0v in and 3.3 v out.

Regarding the rectifiers right after the SMPS transformers, can you help me identify where these are?

[budm]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

You are getting the 5V OK so the rectifier is not the probelm, something went out on that logic board.

[Mrx3750]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

If it's the logic board, I might have a replacement. I still have that Vx2235wm here.

[Red74Corvette]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

I'm interested in the logic board if you still have it.

[Mrx3750]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

Yeah I have it.

Is your monitor's native resolution 1680x1050? If it is then I would think you could just drop the board in. Can't guarantee it would work because you have a different model, but if you want it, PM me and we can work something out.

[lexwalker]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

Help me with terminology please. What is SMPS transformer, Dscaler board, OCP?

SMPS transformer is that small yellow transformer thingy (its actually a high frequency transformer). Dscaler (short for "Digital scaler") board is where the video signal is processed (and scaled if necessary) and then sent to the LCD panel, many unfamiliar with these boards would call it the "logic board". OCP is "Over Current Protection", is used for protecting and shutting down the power circuit in case of shorts and overloads across the outputs.

Regarding voltage regs on the main board, I see two EH16A devices. They both test 5.0v in and 3.3 v out.

Regarding the rectifiers right after the SMPS transformers, can you help me identify where these are?

If you have 5V output then they should be fine. You could still check and see if any of them are open on one side instead of being usually shorted when failed (ie. the reason for checking was the fuse you've mentioned earlier). They look like 3 pin power transistor, but in reality they are 2 diodes with common outuput. They are usually attached/mounted to the heatsink.

[Red74Corvette]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

The two rectifiers measure 0 ohms across the two outside legs but none of the outside legs is shorted to the inside leg.

[budm]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

The two out side pin (Anode) are tied together to form two diodes in parallel, so it will show as shorted circuit. The rectifier is common Cathode (middle pin) Cathode.

[lexwalker]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

The two rectifiers measure 0 ohms across the two outside legs but none of the outside legs is shorted to the inside leg.

Usually have to desolder and pull them out to check. It shows shorted because they are linked to together on the circuit board.

[Red74Corvette]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

Before desoldering and checking the rectifiers, I measured the output voltages at the connector going to the dscaler board. The 5V pin measures 5VDC and 0VAC. The 13.8V pin measures 14.1VDC and 0VAC. Is that any indication that the rectifiers are working properly or should I still pull them out and check?

[lexwalker]

Re: ViewSonic VX2355wm Both Blue and Orange Lights are Lit after Recap

Before desoldering and checking the rectifiers, I measured the output voltages at the connector going to the dscaler board. The 5V pin measures 5VDC and 0VAC. The 13.8V pin measures 14.1VDC and 0VAC. Is that any indication that the rectifiers are working properly or should I still pull them out and check?

When only one side of the rectifier is working, it will still show proper voltage output. Its quite common to find one out of two diodes failed (ie. weak/degraded diode). Just pull them out temporarily to check. Also trace connections related to the fuse you've mentioned earlier to see any other components along those connections has problems (that may have caused the fuse to blow in the first place)...