viewsonic vx2835wm no power

[Lee1]

Re: viewsonic vx2835wm no power

Hi, I am new to this forum. I have been reading lots of post on the Viewsonic VX2835WM, but have not found a list of the capacitors that are on the power supply board for this monitor. This would make it easy to find replacements. Thanks for any help.

[selldoor]

Re: viewsonic vx2835wm no power

We rarely provide lists of caps as we have no idea what version of any particular board might be in your set. The manufacturers sometimes make
amendments to the values they use even on the same board versions.
The best way is to simply list the caps you have on your board and then
look up the datasheets and see what is available at digikey. You need the same voltage and uf value and same or better esr. You should also make
sure they will physically fit.

[badcapass]

Re: viewsonic vx2835wm no power

Hi,

same sort of Problem here with HD281D and PSM217, but there is no voltage on the Output rails, just 5V stand by (~5V, blue LED is on, react on power button, screen works with another power supply). All recapped, but the 400V parts (150muF and 22muF). Checked main capacitor (150muF), round 320V, soldered it out, 140muF, is that ok? Same on the 22muF cap, measured 20muF, both looking good.
Any idea why it stays in standby?

Regards
Paul

[budm]

Re: viewsonic vx2835wm no power

Can we good close up of the power supply board connectors? We are looking for the PS_ON signal to see if the signal (>2.75vdc) is present, also the voltage on that 450VDC main filter cap should go up to 380Vdc measure AT the two LEGS of the cap when power is switched on. Pictures of the main board also.

[badcapass]

Re: viewsonic vx2835wm no power

Hi,

thanks for your help. I soldered all back together and measured the given points. PSON is always 0, but blue LED react on power button... Voltage on main cap is 320V, after blue LED is on it drops to 319V, voltage is constant.

Pics will follow.

Thanks and regards,

Paul

[budm]

Re: viewsonic vx2835wm no power

OK ,the main board is not sending the PS_ON signal to turn on the power supply and the PFC Voltage booster circuit to boost it up to around 380~390VDC.
We need to test the main board next.

[badcapass]

Re: viewsonic vx2835wm no power

.


I thought the main board is ok, because if I replace the power supply with a compatible FSP217 (from another HG281D) it works. But when standby has 5V why there is no PS_ON? I think I get it. But why the blue LED reacts then and why ist goes in standby (blinking) after a while (think at the time where it shows the ‘no signal' screen). Oh, I didn't mention, there is no input connected while testing.
Back to the main board. On the main board three caps are already replaced with 105°C Matsushita (Panasonic), C18 (10muF/50V), C74 (10muF/50V) and C83 (100muF/50V). At the connector from the power supply, there are just the 5V from SB (between black/GND and red/SB). Measured the voltage at the power button, it's always 3.3V, but when the blued LED went of, it shortly drops down.

Hope the pics are god enough. Sorry for full image, thumbnail as link doesn't work:

PSP back a:


PSP back b:


PSP back c:



PSP front c:


PSP front b:


PSP front a:



MB back:


MB front:



Regards and many thanks

Paul


.

[budm]

Re: viewsonic vx2835wm no power

OK, you have to have it connected to running PC, then check the PS_ON again, when it is in standby, the PS_ON will be LO (<1V).

[badcapass]

Re: viewsonic vx2835wm no power

Hi,

connected it to a video signal, PSON fluctuate between 0.01V and 0.9V. When blue LED went off, there is a short peak (0.9V) at PSON, the voltage at power button drops.
Seems like monitor do not wake up from stand by, but with another power supply it will... Are there other Points I can check voltage? By the way, voltage an main cap is today ~ 325V. I have read voltage at main cap is 340V?

Many thanks for your efforts, regards

Paul

[Lumberjack777]

Re: viewsonic vx2835wm no power

I might be able to save you some time here. That appears to be the same power supply used in the Hanns-G 28" monitor. Some of the smaller caps tend to dry out. I normally replace the 3 caps circled in red, and everything fires back up again. You could optionally replace the ones circled in blue, but they have always shown low esr for me; even after years of use. But the 3 in red definitely need to be replaced, and it will probably work.

[badcapass]

Re: viewsonic vx2835wm no power

Hi Lumberjack777,

yes the power supply is from a HG281D. All caps are already replaced with Matsushita (Panasonic) 105°C LowESR types, seems you use the same, thanks for the pic. Just the two 400V are original, I tested them and they are ok. But maybe you can help me with the right sizes. I got the power supply with replaced caps and didn't check them, because I couldn't get a schematic for the board.

Input
C3 150muF/400V main cap (ori)
C203 2.2muF/50V
!C205 10muF/50V !1muF/50V

Middle
!C108 10muF/50V !22muF/50V
!C111 10muF/35V !22muF/50V
C114 2.2muF/50V
C403 470muF/35V
C406 10muF/50V
C601 22muF/400V (ori)
C603 22muF/35V
C606 1muF/100V
C605 47muF/50V
C701 1000muF/35V
C707 22muF/35V

Output
C301 1000muF/35V
C302 1000muF/35V
C306 470muF/35V
C401 1000muF/50V
C502 470muF/35V
!C505 470muF/35V !1000muF/10V
C506 470muF/35V
C702 (470muF/35V?)

Please check values of caps marked with !

Many thanks, regards
Paul

[badcapass]

Re: viewsonic vx2835wm no power

Hi,

after reading some more, I changed C111 to 22muF and C505 to 1000muF. C205 I replaced with 2.2muF, because I have no with 1muF in Stock. So far so god, it's not working at all, but the blue LED doesn't come up anymore... :-( Main Cap is on 318V, 5VSB is on 4.99V, PS_ON between 0.02 and 1.2V, there are 3.3V at power buton. Could the C205 make such a differents? Is C108 10 or 22muF? Any hints, any spots to measure? It has to be the powersupply!

Regards
Paul

[budm]

Re: viewsonic vx2835wm no power

The main board looks like HanG, I see that you replace one of the two caps (100uf/16v) by the two regulators ICs, but not the one to the right as shown in the pictures.

[badcapass]

Re: viewsonic vx2835wm no power

Hi,

yes thats right. I got the TFT with replaced caps, but it neither starts. So I took the power supply from another HG281D and it works! Put back the PSM217 and the Problems were back to. That is the reason why I wrote in this thread for the PSM217, also knowing it's ViewSonic related. Either at the Moment I havn't the caps for the main board. So first I want to concentrate on fixing the power supply.

Regards

Paul

[budm]

Re: viewsonic vx2835wm no power

OK, since you do have the working power supply, I would like what DC voltage you get at the main cap of the good power supply when it is in standby and when it is on. I expect it to be about 325V (230 x 1.414) in standby, about 380V when it is on. I do not have this power supply with me right to do the test.

[Lumberjack777]

Re: viewsonic vx2835wm no power

Yeah budm, he might be the victim of a bad cap change. That's why I always prefer a monitor that has never been touched.

Ok badcapass: fortunately I did get an hg281d in the other day and I just opened it and its untouched

The cap values you requested are.....

C205 = 1uF 50v
C108 = 10uF 35v
C111 = 22uF 35v
C505 = 1000uF 10v

[budm]

Re: viewsonic vx2835wm no power

@Lumberjack777, so what DC voltage do you get at the main cap when it is on?

[badcapass]

Re: viewsonic vx2835wm no power

Hi,

thanks for the input, that are the same values I have read across the net. I measured a voltage at main cap (C3) of 320V. Ordered the missing caps today, waiting to replace the last wrong part (C205 1muF). Hopefully it will change the situation.

Regards
Paul

[badcapass]

Re: viewsonic vx2835wm no power

Hi,

just replaced C205, but nothing changed. I ordered the caps for the main board to and since the blue LED doesn't react anymore I want to recap the mb as well. But as you know, I am not sure about the right dimension. They should fit, but...

Nr. [muF] [V]
C8 10 16
C13 10 16
C14 10 16
C18 10 16
C19 10 16
C60 10 16
C61 10 16
C63 - -
C69 100 16
C74 10 16
C77 10 16
C80 100 16
C83 100 16
C92 10 16
C94 100 16
C97 100 16
C98 470 16
C99 470 16
C103 470 16
C119 10 16
C120 10 16

Edit: Maybe I am totally wrong in a ViewSonic Thread..., sorry.

Regards
Paul

[badcapass]

Re: viewsonic vx2835wm no power

I have to make an addition. Just tried to start up my PSM217 by putting SB5V on PSON, no reaction voltage on +12V or +24V, just a slightly droped votage on main cap C3. Measured voltage on Q601, there it is :
.........|xxxxx|-- 1
.. i - -|Q601|-- 2
.........|xxxxx|-- 3
I get between i/1~20V, i/2~0V, i/3~20V, 1/2~0V, 2/1~20V, 2/3~20V is that correct?

Regards
Paul