Viewsonic VG2230WM-3 - No Power

[benV]

Hi everyone,

I'm trying to fix a Viewsonic VG2230WM-3 with no power. I replaced 6 bulged teapo 470uf 25v with brand new Rubycon capacitors and nothing change. The only new thing that has emerged is a ticking, like a clock, clear and regular.

I checked few things with my multimeter.

I have 165V at the big cap
To the right on the power board, to the logic board i made 5 measurements and here are the results:

BL-ADJ : 0.5 V not stable
GND : 0
GND : 0
+ 5 : 1.2 v to 1.5 v not stable
+ 13.(something unreadable) : 0.1 v to 0.3 v not stable

Below is the picture of both side of the power board.

Thanks for your help.

[retiredcaps]

Re: Viewsonic VG2230WM-3 - No Power

The only new thing that has emerged is a ticking, like a clock, clear and regular.

Ticking suggests the SMPS is trying to start, but can't maybe due to

1) bad startup cap (probably 47uF 50V C102). Measure the DC voltage across this capacitor. It should be stable and enough to power the SMPS IC VCC pin. Measure ESR. If no ESR meter, replace with something like Panasonic FC series.

2) bad SMPS IC (maybe the IC above C102 mounted on the heatsink?). Find the datasheet and see what the startup voltage should be for VCC. See if VCC is shorted to GND.

3) shorted diode (D101, D102). Test diodes to see if they are shorted.

[retiredcaps]

Re: Viewsonic VG2230WM-3 - No Power

There is another diode in the bottom right hand corner by the word "press".

[benV]

Re: Viewsonic VG2230WM-3 - No Power

1) in fact it's a 22uf 50v and i've got 9v to 14v not stable at all across this one (ltec brand) !

2) The chip is a STR W6252. It is not shorted to GND

3) D101 seems to be shorted. D102 is ok

I'will replace the cap and the diode and see what's next.. Thanks retiredcaps.

[benV]

Re: Viewsonic VG2230WM-3 - No Power

There is another diode in the bottom right hand corner by the word "press".

D201 ? Do i have to desoldered it to check it ?

[retiredcaps]

Re: Viewsonic VG2230WM-3 - No Power

D201 ? Do i have to desoldered it to check it ?

No, you can test everything "in circuit" first. If the diode test readings are suspicious, then desolder and verify "out of circuit". Use the diode test function for these tests.

[retiredcaps]

Re: Viewsonic VG2230WM-3 - No Power

Datasheet is at

https://cdn.badcaps-static.com/pdfs/...242a347ec7.pdf

See page 5. VCC(ON) is typically 15.5V. Minimum is 13.9 and maximum is 17.1V DC.

So it looks like the SMPS IC is starting, but the shorted diode is causing the fluctuation.

[jaidiaz]

Re: Viewsonic VG2230WM-3 - No Power

I have the same board too...the problem that I encountered was when I started to turn it on with the lcd panel the power just went down. After that I removed the panel leaving the power board only and turned it on again it works flawlessly. What might be the cause of power failure when I attached the lcd panel and turn it on.

[selldoor]

Re: Viewsonic VG2230WM-3 - No Power

After that I removed the panel leaving the power board only and turned it on again it works flawlessly.

What do you mean? how did you now it worked flawlessly without the panel
being connected.