Yusmart 229IP-P 22" LCD Monitor Dead

[fusionmax]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

Does the fact that the power board is not outputting 24v have a bearing on things?

[retiredcaps]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

Does the fact that the power board is not outputting 24v have a bearing on things?

In general, the 5V DC is used for most or all of the functionality that is required on the logic board. Voltage regulators on the logic board take that 5V DC and change it to 3.3V DC and/or 1.8V DC as required. The power on/off functionality is located on the logic board.

So there is proper voltage on the logic card as you verified. You also verified there is continuity from the keyboard panel to the logic card.

The 12V, 19V, or 24V DC is usually used for the inverter section of the board. There is 24V DC on the power board, but we have not traced it any farther right now because it is not required on the logic board.

If the power LED was lit (any color), then we would be focusing our attention back on the inverter section and tracing out the 24V DC.

[retiredcaps]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

If the trace path that you find happens to lead through an electrolytic capacitor, you might want to replace that one.

The smaller ones found on the logic rarely are bad, but when they are bad, they can fail without any sign of visibly bloating. They can have high ESR (ohms) or be out of uF tolerance.

[alexanna]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

Okay, I can't find a datasheet for TSUMU58HJ-LF, but you may have better luck?

If you find a datasheet, look at the pinout configuration and see if the power on/off signal has the proper voltage reading. If it doesn't, then you have to "back trace" from the TSUMU58HJ-LF to the power on/off and see if one the components in between is good or bad.

If you cannot find a datasheet, you will have to "buzz" out the trace from the power on/off connector to the chip.

I would be really curious about something. Is there any voltage at any of the pins at the front control panel? I would expect to have at least one ground wire and at least several that have a reference voltage I am going to guess 5v may be the reference. If a reference voltage is there on any of the pins dose the voltage go low or to near 0v when different buttons are pushed. The voltages I suggest are just a GUESS, but the monitors I have looked at that I suspected a problem with front control panel have all been able to change the state of the reference voltage[going from a high to low voltage as buttons are pushed]Another thing to concider is that a monitor can work without the front control panel hooked up.

[fusionmax]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

I have checked the voltage at the power button and it reads as 3.4

When I press the button it drops to nothing.

I am having problems tracing the power line to the IC though, the trace just dissapears underneath some other chips and then I lose it!

I have been unable to find a datasheet for it and have even contacted the company that originally made it with no luck

[fusionmax]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

Also, I have been unable to find any fuses on the logic board, does this sound right or should there be some?

[retiredcaps]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

Also, I have been unable to find any fuses on the logic board, does this sound right or should there be some?

It depends on manufacturer. It may be normal to have no fuse on the logic board.

Sometimes the fuse is on the backside, but it is rare.

[alexanna]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

I have checked the voltage at the power button and it reads as 3.4

When I press the button it drops to nothing.

I am having problems tracing the power line to the IC though, the trace just dissapears underneath some other chips and then I lose it!

I have been unable to find a datasheet for it and have even contacted the company that originally made it with no luck

Well the power button is doing something, Whether it being right or wrong I don't know. As retiredcaps suggests a data sheet would be very helpful. I would hope now that someone with a similar monitor may be able to verify if the 3.4v is a correct reading.
Al.

[fusionmax]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

I've been real busy lately but finally managed to find some time last night to try and trace the power button back to the IC. I have attached an image of how far I have got....... not far!

I am still having no luck with finding a datasheet for the IC, the manufacturer haven't come back to me and I can't find anything anywhere

[fusionmax]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

I have also asked Quotidian at the post https://www.badcaps.net/forum/showth...d=1#post125888 if he could measure the voltage he is getting at his power button.

Hopefully this will confirm if mine is ok or not.

[billy66]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

My monitor has the same power and main board as your monitor, but my monitor is an Envision G218a1. Exact same issue, no power. I could check my voltages to compare to yours, but being it is the same issue... I'd assume the readings wouldn't do you any good.

I see you haven't posted in 2 weeks... have you found a fix?

Thanks!

[billy66]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

OK. I've tested all the same tests that fusionmax has. My only difference is:

My cable coming from my power board going to the main board: it has a voltage of 2.82VDC at the black wire (between the white and brown wires).

I also have the same voltage at the control buttons as he does (though being my monitor is dead too, I'm not sure if they are correct).

[fusionmax]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

Hi Billy,

I've not found a fix yet, i'm just working on making a diagram of the logic PCB to make things easier to trace.

I should have something done in the next couple of days so I can post something up.

Have you managed to find a datasheet for either the logic PCB or the IC from the logic board?

[billy66]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

To be honest, I haven't been looking too hard. I have like 4 monitors I'm working on, and upon doing the initial research on this one... I came across your post and thought I could try to help. If I do, I'll post it here of course.

[fusionmax]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

Ok, so I've finally managed to find some time and traced the power button back to the IC on the Logic board.

It appears to be at pin 50 and doesn't go through any capacitors. I have attached some images showing this.

Can anyone give me my next move?

[fusionmax]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

Hate to be a bumper but has anyone got any ideas?

I am at a loss!

[jetadm123]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

At this point, if you go back and take a look at the photo #2, post #11, you will see 4 8-pin chips. I'm using the vx2235 schematic (page 48), and these chips are marked Q905-906 and Q911-912? These chips each contain 2 mosfets. Please check each of them for possible shorts. These chips are responsible for generating the sine wave used by the inverter transformers to generate the high voltage required by the CCFL's. However, if they are shorted will usually blow a fuse, but still worth a look.

[bonney]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

hi I have one of these trying to fix. The vx2235 has the same power board but differnt logic board

forgot to say
mine has only the green power light on, nothing else
last one like this was the eeprom

[jetadm123]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

Hello bonney and welcome to the forum! If you've had a chance to read through this thread, you'll see that there was the question of having 24V on the brown wire on the wiring harness on the power/inverter board. It shows on the viewsonic schematic, but shows up 0V on the Yusmart. We don't know if this normal for the Yusmart or not. Can you please verify?

[bonney]

Re: Yusmart 229IP-P 22" LCD Monitor Dead

Hi Jet and thank you for the welcome

24V does not go to the logic board, if you look at post 11 picture 2 you can just make out no join on pin 9